Emergency Pharmacology: PK, PD & Legal Basics

Table of Contents

Emergency Pharmacology: Introduction, Legal Aspects, Classification, Pharmacokinetics & Pharmacodynamics

Why this lesson matters: In emergency care, a medicine may prevent death, restore a failing physiological function, relieve suffering or create immediate harm when it is selected, calculated, prepared, administered or monitored incorrectly. An emergency medical technician must therefore understand not only the name of a drug, but also the patient, the indication, the route, the expected effect, the time course, the important contraindications and the legal limits of practice.

Learning outcomes

By the end of this lesson, the emergency medicine student should be able to:

Define pharmacology, pharmacotherapeutics, pharmacokinetics, pharmacodynamics, toxicology and clinical pharmacology.
Explain why pharmacology is central to safe emergency assessment and treatment.
Describe the main legal, ethical and professional controls governing medicines in Uganda.
Differentiate chemical, generic and brand names and use generic names accurately.
Classify medicines by source, therapeutic use, body system, mechanism, legal status, route and dosage form.
Explain absorption, distribution, metabolism and excretion (ADME), including first-pass effect, bioavailability, protein binding, half-life, clearance and steady state.
Explain receptor action, agonists, antagonists, dose–response relationships, potency, efficacy, therapeutic index and adverse effects.
Recognise patient and emergency factors that change a drug response and identify when senior clinical or pharmacy support is required.
Apply a structured safety check to a medicine order before administration and respond appropriately to a medication error or suspected adverse drug reaction.

1. What is emergency pharmacology?

Pharmacology is the scientific study of drugs and their interactions with living organisms. It includes the origin, properties, actions, movement, uses and harmful effects of medicines. Emergency pharmacology applies this knowledge to rapidly changing conditions such as shock, trauma, respiratory failure, acute coronary syndromes, seizures, poisoning, anaphylaxis, severe pain and cardiac arrest.

Emergency medicines are often given when there is little time for trial and error. The clinician must make a time-critical decision while considering airway, breathing, circulation, disability, exposure, the likely diagnosis, allergies, pregnancy, kidney and liver function, current medicines and the patient’s ability to absorb or respond to treatment.

Pharmacology is not memorising drug lists. A safe emergency practitioner connects five questions: Why is this medicine needed? Is it safe for this patient? What dose and route are authorised? What effect should occur and when? How will I monitor and respond?

Important branches of pharmacology

Branch	Main question	Emergency-care example
Pharmacokinetics (PK)	What does the body do to the drug?	How quickly an IV medicine reaches the circulation and how kidney failure prolongs its effect.
Pharmacodynamics (PD)	What does the drug do to the body?	How a receptor agonist raises heart rate or relaxes bronchial smooth muscle.
Pharmacotherapeutics	How are medicines used to prevent, diagnose or treat disease?	Selecting a medicine for bronchospasm, pain, hypoglycaemia or seizure.
Toxicology	What harmful effects occur after exposure?	Recognising opioid respiratory depression or pesticide poisoning.
Clinical pharmacology	How do pharmacological principles apply to patients?	Adjusting treatment for age, pregnancy, shock, renal impairment or polypharmacy.
Pharmacovigilance	How are medicine-related harms detected and prevented?	Reporting a serious unexpected reaction or a recurring administration error.

2. Why pharmacology is essential in emergency medicine

Time is critical: a delayed medicine may allow hypoxia, shock, seizure activity or anaphylaxis to worsen.
Physiology is unstable: perfusion, acid–base status, temperature and organ function can change within minutes.
Routes affect speed: IV, intraosseous, intramuscular, inhaled, sublingual, buccal, oral, rectal and topical routes do not produce the same onset.
Many emergency medicines are high-alert: a small error in concentration, dose or route can cause severe harm.
Patients are frequently unable to provide a history: allergy, pregnancy, chronic medicines and substance use may be unknown.
Polypharmacy is common: a patient may already have taken medicines at home, received treatment from another facility or use traditional/herbal products.
Every medicine has a benefit–risk balance: the correct medicine can be life-saving, while an unnecessary medicine can mask deterioration or create a new emergency.

EMT medication-thinking mnemonic — A SAFE DRUG:
Assess the patient and indication Screen allergies and contraindications Authorised order and scope Five-plus rights check Exact concentration and calculation Document before leaving the patient Reassess the response Unexpected effects reported Guard the medicine and patient.

3. Basic terms every emergency student must know

Term	Meaning	Clinical teaching point
Drug	A chemical or biological substance that alters a biological function when introduced into an organism.	Not every drug is a medicine; some are used for diagnosis, prevention or investigation and some are toxic.
Medicine	A prepared product intended to prevent, diagnose, treat or relieve disease or symptoms.	It contains active ingredient(s), excipients and a dosage form such as a tablet, injection or inhaler.
Active pharmaceutical ingredient (API)	The component responsible for the intended pharmacological effect.	Different brands may contain the same API and strength.
Indication	The clinical reason for using a medicine.	The indication must match the patient’s problem; a familiar drug is not automatically appropriate.
Contraindication	A condition in which a medicine should not be used because the risk outweighs benefit.	Some are absolute; others require specialist judgement or dose adjustment.
Precaution	A condition requiring additional assessment, monitoring or modification rather than automatic avoidance.	Examples include pregnancy, asthma, renal impairment, dehydration or a history of allergy.
Adverse drug reaction (ADR)	A harmful and unintended response occurring at normal doses used for treatment, prevention or diagnosis.	Record, treat, report and prevent recurrence.
Side effect	A known secondary effect that may occur at therapeutic doses.	A side effect may be predictable and mild, but it can still become dangerous in a vulnerable patient.
Toxicity	Harm produced by excessive exposure, accumulation, unusual sensitivity or a poisonous substance.	Consider dose, concentration, route, timing, kidney/liver function and interactions.
Half-life (t½)	Time required for the plasma concentration or amount of a drug to fall by 50% during the relevant elimination phase.	It influences dosing intervals and how long an adverse effect may persist.
Therapeutic index	A comparison between toxic and effective exposure.	Narrow-therapeutic-index medicines require careful calculation, monitoring and documentation.

4. Medicines and the Ugandan legal framework

Emergency medical care takes place inside a regulated health system. In Uganda, the National Drug Policy and Authority Act, Cap. 206, established the National Drug Authority (NDA) and provides the framework for controlling the quality, importation, distribution, supply, prescription and appropriate use of medicines. The NDA also publishes medicine guidelines, registers products and regulates licensed outlets. Students must use the current law, institutional policy and professional-council requirements in force at the time of practice.

Legal update for students: Uganda has enacted a National Drug and Health Products Authority Act, 2026, but the publicly available legal record indicates that it had not yet commenced at the time this lesson was prepared. Always check the commencement notice and your facility’s current circulars; do not assume a proposed or enacted-but-uncommenced law has already replaced the operational framework.

The legal framework is designed to protect the public from substandard, falsified, expired, unregistered, misused and improperly supplied medicines. It does not remove the individual practitioner’s duty to assess the patient, follow a lawful order, work within competence and report harm.

Legal controls that affect emergency practice

Product authorisation: use medicines obtained through lawful supply chains and approved or authorised for use in Uganda, unless a recognised emergency-use pathway applies.
Licensing of premises and suppliers: medicine storage, dispensing and distribution are performed through licensed systems; emergency personnel should not source medicines from informal sellers.
Restricted and controlled medicines: some medicines have stricter requirements for prescription, custody, registers, stock reconciliation, administration, wastage and witnessing.
Prescription and order validity: an order should be legible, complete, dated, attributable to an authorised prescriber and clinically appropriate. If it is unclear or unsafe, stop and clarify.
Storage and quality: temperature, light, humidity, security, expiry date, integrity of packaging and cold-chain requirements are part of safe practice.
Documentation and traceability: the patient, medicine, dose, route, time, person giving it, response and any variance should be traceable.
Pharmacovigilance: suspected serious or unusual medicine-related harm should be escalated and reported through the facility and national reporting channels.
Advertising and claims: health workers must not make unsupported claims or promote prescription medicines in ways that breach professional or regulatory rules.

Legal versus ethical responsibility

Situation	Legal/professional duty	Ethical duty
Unclear order: “give adrenaline” without concentration, route or indication	Do not guess; clarify with the authorised prescriber or senior clinician.	Prevent avoidable harm while preserving timely care.
Patient is unconscious and no history is available	Act under emergency protocols and document the assessment and rationale.	Provide necessary care while respecting the patient’s best interests.
Medicine error is discovered after administration	Stabilise, notify the responsible clinician and follow incident-reporting policy.	Be truthful, protect the patient and support learning rather than concealment.
Patient refuses a medicine	Assess capacity, explain consequences, document refusal and seek senior advice.	Respect autonomy while preventing coercion and ensuring informed choice.

5. Scope of practice, delegation and accountability

A student or EMT must know the difference between being present, being trained, being authorised and being accountable. A skill taught in class is not automatically authorised in every clinical setting. The practitioner must work under the relevant professional council, facility protocol, medical direction and emergency-care standing orders.

Do not independently prescribe, alter a prescription, substitute a medicine or give an unfamiliar preparation outside your legal scope.
Confirm which medicines may be administered under a standing order, protocol or direct verbal order.
When a verbal order is permitted in a genuine emergency, repeat it back, confirm the patient and drug details, administer according to protocol, and obtain timely written confirmation.
Never sign for a medicine administered by another person. Each practitioner records their own action.
Ask for help when the patient’s condition, medicine, calculation, route or equipment is beyond competence.
Delegation transfers a task, not the duty to ensure that the person is trained, supervised and supported.
Maintain confidentiality: medication history, diagnosis, toxicology and errors are shared only with people who need the information for care, safety or lawful reporting.

Clinical reasoning scenario: A patient with wheezing is deteriorating. A relative produces an unlabelled bottle and says it is the patient’s “usual injection.” The correct action is not to administer it because the relative is confident. Secure the bottle, identify the patient, assess ABCDE, seek a lawful order and use an identifiable, authorised medicine from the emergency supply. An unknown preparation has unknown concentration, expiry, sterility, interactions and legal traceability.

6. How medicines are named

Name	Explanation	Example of how it matters
Chemical name	Describes the molecular structure using chemical nomenclature.	Useful in chemistry and research but usually impractical for a drug chart.
Generic name (non-proprietary name)	The standard name assigned to the active medicine.	Reduces confusion between brands and supports rational procurement and teaching.
Brand/trade name	Name chosen by a manufacturer for marketing.	Two different brand names may contain the same active ingredient.
Official name	Name recognised by an official pharmacopoeia or national formulary.	Supports standardisation and quality assurance.

Student rule: Learn the generic name, strength, dosage form, usual emergency indication, major contraindications, high-risk effects and monitoring requirements. Use the brand only to identify the product at hand.

7. Classification of medicines

Classification is a way of organising medicines so that their properties, uses and risks can be understood. One medicine can belong to several classifications at the same time. For example, salbutamol is a synthetic medicine, a bronchodilator, a respiratory-system medicine, a selective beta-2 agonist and an inhaled preparation.

7.1 Classification by source

Natural: obtained from plants, animals, minerals or microorganisms, for example some alkaloids, hormones, vaccines and antibiotics.
Semi-synthetic: a natural molecule chemically modified to improve activity, stability, absorption or safety.
Synthetic: produced through chemical synthesis.
Biological and biotechnology-derived: vaccines, monoclonal antibodies, recombinant proteins, blood products and other products made from living systems.

7.2 Classification by therapeutic purpose

Purpose	Function	Examples of emergency relevance
Preventive	Reduces the chance of disease or complication.	Vaccines, post-exposure prophylaxis and thrombosis prevention where authorised.
Diagnostic	Assists identification or measurement of disease.	Contrast media, diagnostic dyes and some challenge tests.
Curative/etiological	Acts on the cause of disease.	Antimicrobials for a confirmed or strongly suspected infection under protocol.
Symptomatic	Relieves a symptom without necessarily removing the cause.	Analgesics, antiemetics and antipyretics.
Replacement	Replaces a deficient substance.	Glucose, electrolytes, hormones and blood products under authorised indications.
Supportive/resuscitative	Supports a failing physiological function.	Fluids, oxygen, vasopressors and medicines supporting cardiac or respiratory function.
Palliative	Relieves suffering and improves comfort.	Carefully titrated analgesia, antiemetics and symptom control.

7.3 Classification by body system

Examples include cardiovascular, respiratory, nervous-system, endocrine, gastrointestinal, urinary, reproductive, musculoskeletal, anti-infective, dermatological and haematological medicines. This approach helps students link a medicine to anatomy and disease, but it can be misleading because one medicine may act on more than one system.

7.4 Classification by pharmacological action

Agonists: activate a receptor to produce a response.
Antagonists: bind to a receptor and reduce or block the action of an agonist.
Enzyme inhibitors: slow or block an enzyme-mediated reaction.
Ion-channel modulators: alter movement of ions such as sodium, calcium, potassium or chloride.
Hormone or receptor replacement: supplies a substance or mimics a physiological signal.
Osmotic agents: change water movement by altering osmotic pressure.
Anti-infectives: inhibit or kill bacteria, viruses, fungi or parasites.
Immunomodulators: increase, decrease or redirect immune activity.

7.5 Classification by legal supply status

National law and medicine schedules determine which products require a prescription, which may be supplied through authorised outlets, and which require special controls. Categories may include prescription-only medicines, pharmacy or professional-supply medicines, over-the-counter medicines, controlled or narcotic medicines, and restricted medicines. The exact schedule and permitted prescriber or dispenser must be checked in current Ugandan law, the National Formulary and institutional policy.

Do not confuse “available in an emergency tray” with “free to use.” A medicine can be physically present but still require an authorised order, protocol indication, expiry check, witnessing, controlled-drug register entry or senior review.

7.6 Classification by route and dosage form

Route/form	Strengths	Important limitations and hazards
Oral tablets, capsules and liquids	Convenient, usually safe and economical.	Slow or unreliable during vomiting, shock, reduced consciousness, ileus or aspiration risk.
Sublingual/buccal	Rapid absorption and avoids much first-pass metabolism.	Requires cooperation and intact mucosa; do not swallow or chew unless directed.
Intravenous	Immediate bioavailability and precise titration.	Rapid toxicity, dosing errors, extravasation, infection and incompatibility risk.
Intraosseous	Rapid access when IV access is difficult in critical illness.	Requires trained insertion, correct device use and monitoring for complications.
Intramuscular/subcutaneous	Useful when oral or IV routes are unsuitable.	Absorption may be poor in shock; bleeding, pain, nerve injury or tissue injury may occur.
Inhaled/nebulised	Targets the respiratory tract and can act quickly.	Technique, device, respiratory effort and aerosol precautions affect delivery.
Rectal	Alternative when oral route is unavailable; may be useful for some anticonvulsants or antipyretics.	Absorption is variable; dignity, consent, bleeding and local contraindications matter.
Topical/transdermal	Local effect or slow sustained systemic delivery.	Damaged skin, heat, occlusion and dose stacking can alter absorption.

8. Medication safety before pharmacology becomes practice

Medication safety is a system of checks, communication and monitoring rather than a single memory trick. WHO identifies prescribing, transcribing, dispensing, administration and monitoring as stages at which errors can occur. High-alert medicines, transitions of care, polypharmacy, look-alike/sound-alike names, interruptions and poor environmental conditions increase the risk.

The emergency medication safety check

Identify the patient: use at least two identifiers according to facility policy. Never identify a patient by bed number alone.
Confirm the indication: link the medicine to the clinical problem and current assessment.
Check the order or protocol: medicine, concentration, dose, route, frequency or repeat instructions, prescriber and date/time.
Check allergies and previous reactions: ask the patient, relatives, record and team; distinguish a side effect from a true allergy when possible.
Check the product: generic name, strength, dosage form, expiry date, batch, packaging integrity, clarity and storage conditions.
Calculate and measure: write the calculation, confirm units and use an independent double-check for high-alert medicines.
Check route and equipment: compatible line, dilution, flush, device, oxygen source, nebuliser, infusion pump or monitoring equipment.
Explain and obtain cooperation: tell the patient what is being given, why, expected effects and important symptoms to report, unless immediate life-saving treatment makes explanation impossible.
Administer safely: remain with the patient when appropriate and do not leave an unlabeled syringe or prepared dose unattended.
Monitor and document: record the administration and reassess the patient’s response and adverse effects.

Rights of medication administration: right patient, right medicine, right indication, right dose, right route, right time, right documentation, right assessment, right response and right to refuse. The “rights” support clinical reasoning; they do not replace reading the order, checking the label or following local policy.

9. Pharmacokinetics: what the body does to a drug

Pharmacokinetics (PK) describes the time course of a medicine in the body. The classic framework is ADME: absorption, distribution, metabolism and excretion. PK helps explain onset, peak effect, duration, accumulation, toxicity and why the same dose can affect two patients differently.

Clinical translation: A drug may be correctly selected yet fail because it was not absorbed, did not reach the target, was rapidly metabolised, accumulated because clearance was poor, or was given by a route that did not match the emergency.

9.1 Liberation

Before absorption, the active ingredient must be released from its dosage form. A tablet disintegrates and dissolves; a modified-release product is designed to release medicine gradually; an injection is already in solution or suspension. Crushing a modified-release or enteric-coated preparation may cause dose dumping, toxicity or loss of protection. Never crush or split a product unless the label, pharmacist or protocol confirms that it is safe.

9.2 Absorption

Absorption is movement of a drug from its site of administration into the systemic circulation. It is influenced by blood flow, surface area, membrane permeability, lipid solubility, pH, formulation, gastric emptying, intestinal motility and interactions with food or other medicines.

Factor	Effect on absorption	Emergency example
Blood flow	Higher perfusion generally increases uptake; poor perfusion delays uptake.	IM absorption can be unreliable in severe shock or peripheral vasoconstriction.
Surface area	Larger absorptive surface usually permits more uptake.	The small intestine is important for many oral medicines.
Gastrointestinal motility	Changes in transit alter time available for absorption.	Vomiting, ileus or severe diarrhoea can make oral dosing unreliable.
pH and ionisation	Un-ionised, lipid-soluble molecules often cross membranes more readily.	Changes in gastric pH or antacid use can alter some medicines.
Food and binding	Food can delay, reduce or increase absorption; some medicines bind to minerals.	Always check whether a medicine should be given with food or separated from iron/calcium.
Formulation	Solutions usually act faster than tablets; modified-release products act longer.	Do not substitute dosage forms casually in an emergency.

Routes and relative bioavailability

Bioavailability (F) is the fraction of an administered dose that reaches systemic circulation in active form. IV administration is considered 100% bioavailable. Oral medicines may have lower bioavailability because of incomplete absorption, degradation in the gut or first-pass metabolism.

Route	Usual onset pattern	First-pass effect	Key emergency caution
IV	Fastest; effect may begin within seconds to minutes.	Bypassed.	Small errors may cause immediate severe toxicity; give slowly when required and monitor.
IO	Rapid systemic access in critical illness.	Bypassed.	Use only trained protocols and confirm patency.
IM	Minutes; varies with perfusion and formulation.	Mostly bypassed.	May be delayed in shock; consider bleeding risk and site safety.
Oral	Usually slower and variable.	Often present.	Unsafe or ineffective in unconscious, vomiting or aspiration-risk patients.
Sublingual/buccal	Rapid when mucosa is intact.	Reduced or bypassed.	Do not give if the patient cannot protect the airway or follow instructions.
Inhaled	Rapid local respiratory effect.	Variable; much of swallowed fraction may be oral.	Device technique and patient effort determine delivered dose.

First-pass metabolism

After an oral dose, absorbed medicine from the gut enters the portal circulation and may be metabolised in the intestinal wall and liver before reaching systemic circulation. This is the first-pass effect. A large first-pass effect lowers bioavailability and can make oral dosing very different from IV dosing. Sublingual, buccal, transdermal, inhaled and parenteral routes may reduce or bypass part of this effect.

9.3 Distribution

Distribution is the reversible movement of a drug from blood into tissues and body fluids. It depends on blood flow, capillary permeability, lipid solubility, tissue binding, plasma-protein binding and barriers such as the blood–brain barrier.

Highly perfused organs—brain, heart, liver and kidneys—often receive drug earlier than muscle, fat and poorly perfused tissue.
Low albumin can increase the free fraction of highly protein-bound drugs and potentially increase effect or toxicity.
Acidosis, hypothermia, shock and altered membrane permeability may change distribution in critically ill patients.
Fat-soluble medicines may accumulate in adipose tissue and have a longer apparent duration.
Large fluid shifts, oedema, ascites, burns and aggressive fluid resuscitation can change the volume in which a medicine distributes.

Protein binding and free drug

Many medicines bind reversibly to albumin or other plasma proteins. The bound fraction is usually not readily able to cross membranes or interact with receptors; the unbound fraction is available for distribution, action, metabolism and excretion. A low total plasma concentration does not always mean low pharmacological activity if the free fraction is increased.

Body barriers

Barrier/compartment	Why it matters
Blood–brain barrier	Restricts many polar medicines; inflammation, age and certain diseases may alter penetration.
Placenta	Many medicines cross to the fetus. Pregnancy requires a benefit–risk assessment and specialist guidance.
Breast milk	Some medicines enter milk; consider the infant’s age, prematurity and vulnerability.
Testes and other protected tissues	Special barriers may limit distribution and affect treatment of infection or inflammation.

9.4 Metabolism (biotransformation)

Metabolism chemically changes a medicine, commonly in the liver, to make it easier to eliminate. It may inactivate a drug, activate a prodrug, produce an active metabolite or produce a toxic metabolite. The intestine, kidneys, lungs, plasma and other tissues can also contribute.

Stage	Typical reaction	Clinical meaning
Phase I	Oxidation, reduction or hydrolysis, often involving cytochrome P450 enzymes.	May inactivate the medicine, activate a prodrug or create a reactive metabolite.
Phase II	Conjugation such as glucuronidation, sulfation or acetylation.	Often produces a more water-soluble metabolite for excretion, though exceptions occur.

Enzyme induction increases enzyme activity over time and may reduce the effect of some medicines. Enzyme inhibition decreases metabolism and may increase concentration and toxicity. Interactions can occur with prescription medicines, alcohol, herbal products, food and environmental exposures.

Liver factors that alter metabolism

Reduced hepatic blood flow may lower delivery of high-extraction medicines to the liver.
Hepatocellular injury may reduce metabolic capacity.
Low albumin can increase the free fraction of protein-bound medicines.
Neonates have immature enzyme pathways; older adults may have reduced reserve and polypharmacy.
Sepsis, hypoxia, fever, hypothermia and major trauma can change enzyme activity and perfusion.
Drug interactions may become more dangerous when several medicines compete for the same enzyme or transport system.

9.5 Excretion

Excretion removes unchanged medicine or metabolites from the body. The kidneys are the major route for many water-soluble products, but bile and faeces, lungs, sweat, saliva and breast milk can also contribute.

Renal process	Explanation	Clinical relevance
Glomerular filtration	Unbound drug passes from plasma into the renal filtrate.	Low renal perfusion or low filtration can reduce elimination.
Tubular secretion	Transporters actively move selected drugs from blood into the tubule.	Drugs may compete for transporters and alter one another’s clearance.
Tubular reabsorption	Some drugs move back from urine into blood, influenced by lipid solubility and urine pH.	Urine alkalinisation or acidification may matter in selected poisonings under specialist protocol.

Before giving a renally cleared medicine, look for urine output, kidney history, creatinine/eGFR when available, dehydration, age and nephrotoxic co-medications. Emergency treatment should not be delayed for a laboratory result when a time-critical indication exists, but the result should guide subsequent dosing and monitoring.

10. Pharmacokinetic measurements used in emergency care

Parameter	Meaning	Why an EMT should care
Onset	Time from administration to initial clinically detectable effect.	Guides reassessment and prevents premature repeat dosing.
Peak	Time or concentration at the greatest effect or highest plasma level.	Helps anticipate adverse effects and assess whether treatment has worked.
Duration	How long the clinically useful effect lasts.	A short-acting medicine may need repeat dosing or infusion; a long-acting one may continue after transfer.
Clearance (CL)	Volume of plasma from which drug is completely removed per unit time.	Reduced clearance can produce accumulation and toxicity.
Volume of distribution (Vd)	An apparent volume relating the amount of drug in the body to the plasma concentration.	Large Vd may require a larger loading dose but does not mean the patient has a large physical fluid volume.
Half-life (t½)	Time for concentration to decrease by half during elimination.	Usually affects dosing interval and time to wash out after stopping.
Steady state	Approximate balance between drug entering and leaving during repeated dosing or infusion.	Many medicines require several half-lives to approach a stable concentration.
Bioavailability (F)	Fraction reaching systemic circulation unchanged.	Route changes may require a different dose or careful monitoring.

Half-life and accumulation

For many drugs with first-order elimination, about one half-life removes 50% of the amount, two half-lives remove about 75%, three remove about 87.5%, four about 93.75% and five about 96.9%. These are teaching approximations, not a promise for every patient or every drug.

Clinical interpretation: a patient who receives repeat doses before the previous dose has been eliminated may accumulate medicine. Accumulation is more likely when the dosing interval is short, the half-life is long, kidney/liver function is poor, or the dose is excessive.

Loading dose and maintenance dose

Loading dose: a larger initial dose used to reach a target concentration more quickly, especially when the medicine has a large volume of distribution or a long half-life.
Maintenance dose: a repeated dose or infusion intended to replace what is eliminated and maintain the desired effect.
Loading dose is influenced more by volume of distribution and target concentration; maintenance dose is influenced more by clearance and dosing interval.
Never calculate or give a loading dose from memory when a protocol, weight, concentration or patient factor is uncertain. Use a verified reference and an independent check.

First-order and zero-order elimination

Pattern	What is removed	Teaching point
First-order	A constant proportion per unit time.	Most medicines follow this pattern within usual therapeutic ranges; the half-life is relatively predictable.
Zero-order	A constant amount per unit time because elimination pathways are saturated.	Small dose increases may produce disproportionate rises in concentration and toxicity.

11. Pharmacodynamics: what a drug does to the body

Pharmacodynamics (PD) describes the biochemical and physiological effects of a medicine, including receptor binding, signal transduction, dose–response relationships, therapeutic effects and adverse effects. PK determines exposure at the site of action; PD determines what that exposure does.

PK versus PD: PK = the patient changes the drug. PD = the drug changes the patient.

11.1 Drug targets

Target	How a medicine acts	Emergency relevance
Receptor	Binds and activates, blocks or modulates a signalling protein.	Bronchodilation, analgesia, sedation, vasoconstriction and reversal of toxicity.
Enzyme	Inhibits or stimulates an enzyme and changes production or breakdown of a mediator.	Changes inflammation, coagulation, blood pressure or neurotransmitter activity.
Ion channel	Opens, closes or blocks a channel controlling membrane excitability.	Alters cardiac rhythm, seizure activity, nerve conduction or muscle contraction.
Transporter/pump	Changes movement of a substance across a membrane.	Affects neurotransmitters, electrolytes, gastric acid or renal handling.
Nucleic acid/ribosome	Changes genetic expression or protein synthesis.	Important for anti-infectives and some anticancer medicines.
Physical/chemical target	Acts through osmotic, neutralising, chelating or barrier effects rather than a receptor.	Fluids, antacids, adsorbents and selected antidotes.

11.2 Agonists, antagonists and modulators

Full agonist: activates a receptor and can produce the maximum response of that system.
Partial agonist: activates the receptor but produces a lower maximum response, even when all receptors are occupied.
Competitive antagonist: competes at the same receptor site; increasing agonist concentration may overcome the block in a simplified model.
Non-competitive or irreversible antagonist: reduces the available receptor response in a way that may not be overcome by more agonist.
Allosteric modulator: binds at another site and changes receptor response to the natural mediator or agonist.

11.3 Dose–response relationship

A dose–response curve links the amount or concentration of a medicine to the intensity of an effect. As dose rises, response usually increases until a ceiling is reached. Beyond the useful range, adverse effects may rise without additional benefit.

Concept	Meaning	Common exam mistake
Potency	Amount or concentration required to produce a specified effect.	Assuming the more potent medicine is automatically better or safer.
Efficacy	Maximum effect a medicine can produce in that system.	Confusing a high dose with a high maximum effect.
Affinity	Strength of attraction between a drug and its target.	Assuming binding alone guarantees a clinical response.
Selectivity	Preference for one target over others at therapeutic concentrations.	Forgetting that selectivity can decrease at high concentrations.
Therapeutic window	Concentration range where benefit is likely and toxicity is acceptably low.	Using a single “safe dose” without considering the patient and route.

12. Therapeutic index, adverse effects and safety margin

The therapeutic index compares the dose or concentration associated with toxicity with that associated with benefit. A wide therapeutic index generally gives more room for error; a narrow therapeutic index demands precise dosing and monitoring. The apparent safety margin changes with age, organ function, interactions, route and the patient’s disease.

Types of unwanted medicine effects

Effect	Description	Emergency response
Predictable side effect	Known secondary effect related to the pharmacology.	Assess severity, provide support, adjust or stop only under authorised direction.
Type A adverse reaction	Augmented, dose-related and often predictable from the drug’s action.	Withhold/adjust according to protocol, treat the effect and report when required.
Type B adverse reaction	Bizarre, unpredictable, often immune or idiosyncratic.	Stop exposure when appropriate, treat as an emergency and record the reaction clearly.
Allergic reaction	Immune-mediated response ranging from rash to anaphylaxis.	Assess ABCDE immediately and activate the anaphylaxis pathway for severe features.
Drug toxicity	Harm caused by excessive concentration, dose, accumulation or impaired elimination.	Stop further exposure, support ABCDE, identify product/time/amount and contact toxicology or senior support.
Drug interaction	Another medicine, food, disease or substance changes effect or exposure.	Check the full medication history and monitor for loss of effect or toxicity.
Withdrawal	Symptoms after abrupt reduction or stopping of a medicine to which the body has adapted.	Recognise the syndrome and seek a supervised plan; do not abruptly stop essential therapy without advice.

13. Factors that modify drug response

Two patients receiving the same dose may have very different plasma concentrations and clinical responses. Emergency students should assess patient factors before giving a medicine and continue reassessment after it is given.

Factor	How it can change PK/PD	Practical question
Age	Neonates have immature metabolism and renal function; older adults may have reduced clearance and increased sensitivity.	Is this a child, frail older adult or very elderly patient requiring weight-based/specialist dosing?
Body weight and composition	Changes distribution and dose calculations; obesity and oedema alter apparent volume.	Which weight does the protocol require: actual, ideal, lean or estimated?
Pregnancy	Changes plasma volume, renal flow, protein binding and enzyme activity; the fetus may be exposed.	Could the patient be pregnant, and is the indication time-critical?
Kidney disease	Reduces renal elimination and may alter fluid/electrolyte balance.	What is the urine output, kidney history and latest renal result if available?
Liver disease	May reduce metabolism, protein synthesis and detoxification.	Is there jaundice, ascites, chronic liver disease or bleeding tendency?
Shock and hypoperfusion	Changes absorption, distribution, metabolism and clearance; peripheral IM/SC absorption may be unreliable.	Is the chosen route dependable in this circulation?
Acid–base disturbance	Changes ionisation, protein binding and receptor response.	Could severe acidosis or alkalosis alter drug distribution or toxicity?
Temperature	Hypothermia may slow metabolism and alter enzyme, receptor and cardiovascular responses.	Could the patient be hypothermic, febrile or exposed?
Genetic variation	Enzyme and receptor differences can alter metabolism or response.	Unexpected response should prompt reassessment, not automatic repeat dosing.
Current medicines and substances	Interactions, additive sedation, enzyme effects and duplicate therapy may occur.	What has the patient taken today, including herbal products, alcohol and recreational drugs?
Psychological and social factors	Adherence, understanding, fear, access and cultural beliefs affect outcomes.	Can the patient understand and safely follow the plan after discharge or transfer?

14. Drug interactions

An interaction occurs when one medicine, substance, food or disease changes the effect or exposure of another. Interactions may be pharmacokinetic—changing ADME—or pharmacodynamic—changing the response without necessarily changing concentration.

Interaction type	Example pattern	Risk in emergency care
Absorption interaction	Binding in the gut, altered pH or changed gastric emptying.	Treatment failure or delayed onset.
Distribution interaction	Displacement from protein binding or altered tissue uptake.	Transient rise in free drug and toxicity in vulnerable patients.
Metabolic inhibition	One substance slows enzyme-mediated metabolism of another.	Unexpectedly high concentration or prolonged effect.
Metabolic induction	One substance increases enzyme activity over time.	Reduced effect and treatment failure.
Renal interaction	Changes filtration, secretion, reabsorption or renal perfusion.	Accumulation or kidney injury.
Additive effect	Two agents produce similar effects, such as sedation, hypotension or bleeding.	Respiratory depression, falls, shock or uncontrolled bleeding.
Antagonistic effect	One medicine reduces the action of another.	Failure of bronchodilation, analgesia, seizure control or resuscitation.
Synergistic effect	Combined effect is greater than expected from either medicine alone.	Severe toxicity despite apparently ordinary doses.

High-risk interaction example: A drowsy trauma patient has already received an opioid by a first team. A second team considers giving a sedative for agitation without obtaining the medication history. The combined central nervous system depression may worsen hypoventilation and airway obstruction. Reassess ventilation, obtain handover information and seek senior direction before adding another sedating medicine.

15. Tolerance, tachyphylaxis, dependence and withdrawal

Tolerance: a reduced response after repeated exposure, so a larger dose may be needed for the same effect. It may be pharmacokinetic or pharmacodynamic.
Tachyphylaxis: a rapid decrease in response after closely repeated doses.
Physical dependence: physiological adaptation in which abrupt cessation causes withdrawal symptoms.
Psychological dependence: compulsive craving or use despite harm; it is not identical to physical dependence.
Withdrawal: the predictable or dangerous syndrome that may follow abrupt reduction or stopping. Emergency care may require airway support, glucose, seizure precautions, fluids, antidote or specialist review depending on the substance.

16. Medicines in common emergency physiology

Shock and poor perfusion

Peripheral perfusion may be too poor for reliable IM or SC absorption.
Reduced liver and kidney blood flow can slow metabolism and clearance.
Hypoalbuminaemia, acidosis and fluid shifts can change free drug and distribution.
Hypotension and hypoxia increase sensitivity to sedatives, vasodilators and respiratory depressants.
Use the route and medicine specified by the emergency protocol, establish access according to scope, and reassess perfusion after every intervention.

Burns and major trauma

Early fluid shifts can change the volume of distribution; later oedema and altered protein binding may change exposure.
Damaged skin makes some topical or transdermal routes unreliable.
Pain, anxiety, hypothermia and inhalational injury alter physiological response to sedatives and analgesics.
Use weight, injury pattern, perfusion, renal function and repeated observation rather than a one-time assumption.

Pregnancy and breastfeeding

Treat life-threatening maternal illness promptly; maternal hypoxia and shock also endanger the fetus.
Check pregnancy status when it will change medicine choice, dose or monitoring, but do not delay life-saving treatment in a critical emergency.
Consider gestational age, placental transfer, fetal effects and breastfeeding exposure; consult an authorised prescriber or pharmacist.

Children and older adults

Children commonly require weight-based calculations, age-specific concentrations and a dose-volume check.
Never assume an adult concentration is safe for a child; look-alike syringes and decimal errors are dangerous.
Frailty, reduced renal function, polypharmacy and increased sensitivity make older adults vulnerable to hypotension, confusion, falls and sedation.

17. Safe medication calculations

Calculations must be verified using the actual product concentration and the authorised prescription or protocol. Write units at every step and obtain an independent check for high-alert medicines.

Common teaching formula:
Volume to give = (Prescribed dose ÷ Dose available) × Volume containing the dose available

Weight-based dose = dose per kg × patient weight in kg
Infusion rate = total volume ÷ total time
Always check whether the protocol specifies a maximum single dose, maximum daily dose, dilution, concentration, minimum age, repeat interval or renal adjustment.

Calculation safety checklist

Read the prescription aloud and identify the patient.
Write the prescribed dose and units exactly as ordered.
Write the concentration on the label and confirm whether it is per mL, per ampoule, per tablet or per vial.
Convert units only when necessary and write the conversion.
Calculate the volume and estimate whether it is clinically plausible.
Check the maximum dose and the patient’s weight, age, renal/liver status and allergy.
Ask another qualified practitioner to independently check high-alert calculations.
Label any prepared syringe or infusion and document the final dose given.

18. Clinical scenarios for EMT students

Scenario 1 — Unclear concentration: The order says “give 1 mL of adrenaline,” but the tray contains two concentrations. Reasoning: stop, identify the indication and protocol, confirm concentration, calculate the correct dose and obtain a second check. “1 mL” is not a complete dose.

Scenario 2 — Shock and IM absorption: A shocked patient has cold, clammy limbs and weak pulses. An IM medicine is considered. Reasoning: circulation may not deliver the dose reliably. Use the authorised emergency route and establish access according to protocol; do not assume the IM dose has failed and repeat it prematurely.

Scenario 3 — Reduced consciousness: A patient cannot swallow safely but has an oral prescription. Reasoning: protect the airway, do not force oral medicine, assess glucose and ABCDE, and seek an authorised alternative route.

Scenario 4 — Renal impairment: A patient with very low urine output needs a renally cleared medicine. Reasoning: the indication may still be urgent, but dose, interval and monitoring require senior or pharmacy review. Document kidney findings and reassess for accumulation.

Scenario 5 — Allergy history: The patient reports facial swelling after a previous medicine but cannot remember its name. Reasoning: treat the history as clinically significant until clarified, document the description, avoid the suspected product/class where possible and seek an alternative.

Scenario 6 — Post-administration deterioration: After a medicine, the patient becomes drowsy with slow breathing. Reasoning: treat it as a possible adverse effect or overdose: call for help, assess airway and breathing, provide support within scope, identify the medicine and time, monitor continuously, and report/document the event.

19. Responding to medication errors

A medication error may occur during prescribing, transcribing, dispensing, preparation, administration or monitoring. An error can occur even if no harm reaches the patient; near misses are valuable safety information.

Protect the patient first: stop the error or further exposure when safe and assess ABCDE.
Call for clinical help: do not manage a serious exposure alone.
Identify exactly what happened: patient, medicine, strength, amount, route, time, batch, symptoms and other medicines.
Provide monitoring and treatment: follow the relevant emergency or toxicology protocol.
Notify the responsible clinician and supervisor promptly.
Communicate honestly with the patient and family according to policy and senior guidance.
Document facts, not blame: use objective language, times, observations, actions and response.
Complete the incident and pharmacovigilance report through the approved system, even when the patient appears well.
Preserve evidence: keep the packaging, syringe, ampoule or record for investigation when instructed.

Never conceal a medication error. Delay in disclosure can delay treatment, increase harm and prevent the system from correcting the cause.

20. Documentation that supports safe pharmacology

Good documentation is a clinical handover, a legal record and a quality-improvement tool. Record enough information for another practitioner to understand what was considered, what was given and what happened next.

Document	Minimum useful content
Medicine administration record	Patient identifiers, generic name, dose, concentration, route, date/time, signature or electronic identity, and any required witness.
Emergency record	Indication, patient assessment, order/protocol, time prepared and given, response, vital signs and adverse effects.
Controlled-drug register	Stock balance, patient, medicine, strength, quantity, prescriber, administering practitioner, witness and wastage according to facility policy.
Handover	Medicine given, time, effect, remaining concerns, next due time, allergies, reactions and monitoring plan.
Incident/ADR report	Objective description of the event, product details, sequence, patient outcome, immediate actions and people notified.

21. High-yield comparison: pharmacokinetics versus pharmacodynamics

Question	Pharmacokinetics	Pharmacodynamics
Core phrase	What the body does to the drug.	What the drug does to the body.
Main processes	Absorption, distribution, metabolism and excretion.	Receptor binding, signal transduction and physiological response.
Main variables	Bioavailability, clearance, volume of distribution, half-life and concentration.	Potency, efficacy, affinity, selectivity and therapeutic index.
What changes it?	Route, perfusion, food, organ function, enzymes, age and body composition.	Receptor number, disease state, tolerance, genetics, age and interacting substances.
Emergency question	How quickly and for how long will the patient be exposed?	What effect should occur, how strong should it be and what toxicity should I watch for?

22. Examination and revision questions

Define pharmacology and explain how emergency pharmacology differs from general pharmacology.
Differentiate pharmacokinetics from pharmacodynamics using one emergency example for each.
What does ADME stand for?
Explain first-pass metabolism and name routes that partly bypass it.
Define bioavailability, clearance, volume of distribution and half-life.
Why can an intramuscular medicine be unreliable in severe shock?
Explain the difference between a generic name and a brand name.
Classify a medicine by source, therapeutic purpose, body system, mechanism, legal status, route and dosage form.
What is the difference between an indication, contraindication and precaution?
Describe the legal significance of the National Drug Policy and Authority Act in Uganda.
Why must students verify the current law, professional-council requirements and facility policy?
What is the difference between an agonist, partial agonist and antagonist?
Differentiate potency from efficacy.
What is a therapeutic window and why are narrow-therapeutic-index medicines high risk?
List ten rights or safety checks before administering an emergency medicine.
How can renal impairment lead to medicine accumulation?
Explain enzyme induction and enzyme inhibition.
List patient factors that can modify drug response in an emergency.
What immediate steps should follow a suspected medication error?
Why is documentation part of clinical care rather than clerical work?

23. Key takeaways

Pharmacology links a medicine’s identity, indication, legal status, route, dose, expected effect and potential harm.
PK follows the medicine through ADME; PD explains the response produced at the target.
Emergency physiology changes drug behaviour: shock, organ failure, age, pregnancy, burns, temperature and acid–base disturbance matter.
Classification helps organise medicines, but the same medicine can belong to several categories.
Generic names, verified concentrations and clear units reduce confusion.
Legal authority, scope of practice, standing orders and institutional policies must be checked before administration.
Medication safety requires identification, indication, allergy check, correct product, calculation, route, monitoring and documentation.
When an error occurs, protect the patient, call for help, document honestly and report through the correct system.

References and further study

Clinical note: This is an educational revision resource for emergency medical-care students. It does not replace a current Ugandan treatment guideline, authorised prescription, medical direction, pharmacist review, poison-centre advice or local institutional protocol. Always verify the current product label, concentration, patient-specific factors and scope of practice before administration.