Urinary System Medicines: UTI & AKI Care

Urinary System Medicines: UTIs, Stones, AKI and Renal Safety

Why this topic matters in emergency medical care

The kidneys regulate fluid, electrolytes, acid–base balance, blood pressure and drug elimination. Urinary medicines can relieve obstruction, treat infection, alter blood pressure, remove fluid, correct electrolyte emergencies or replace renal function. However, the same medicines can worsen acute kidney injury (AKI), accumulate to toxic levels or hide a life-threatening obstructed infection.

This lesson is for EMT and nursing education. Use current Uganda Ministry of Health guidance, local antimicrobial policies, prescriber orders, renal dosing references and age-specific protocols in practice.

Learning outcomes

Explain renal filtration, tubular handling, urine concentration and the renin–angiotensin–aldosterone system.
Classify urinary antimicrobials, diuretics, analgesics for renal colic, alpha blockers, medicines for overactive bladder and renal-protective therapies.
Recognise cystitis, pyelonephritis, urosepsis, obstructed infected kidney, AKI, chronic kidney disease, renal colic and electrolyte emergencies.
Apply safe renal dose and route principles, fluid assessment, urine monitoring and medicine reconciliation.
Identify nephrotoxins, interactions, pregnancy considerations, dialysis issues and escalation triggers.

1. Renal physiology and medicine targets

Each nephron filters plasma at the glomerulus, reabsorbs and secretes solutes through the tubules, and concentrates urine through the loop of Henle and collecting duct. The kidneys activate vitamin D, release erythropoietin and regulate renin. Reduced renal function changes drug clearance, fluid balance, potassium, acid–base status and blood pressure.

Target	Physiological role	Medicine examples	Emergency relevance
Renin–angiotensin–aldosterone system	Maintains vascular tone and sodium retention	ACE inhibitors, ARBs, mineralocorticoid antagonists	Protective in selected CKD but can worsen AKI or hyperkalaemia during dehydration.
Loop sodium–potassium–chloride cotransporter	Concentrates urine and reabsorbs sodium	Furosemide	Rapid diuresis for pulmonary oedema; electrolyte depletion and ototoxicity risk.
Distal sodium–chloride transporter	Regulates sodium and calcium handling	Thiazide diuretics	Hypertension and stone prevention; hyponatraemia, hypokalaemia and hyperglycaemia.
Collecting duct epithelial sodium channel/aldosterone receptor	Sodium retention and potassium excretion	Amiloride, spironolactone	Useful in selected heart failure/aldosterone excess; hyperkalaemia can be fatal.
Vasopressin V2 receptor	Water reabsorption via aquaporins	Desmopressin, vasopressin antagonists	Controls diabetes insipidus or selected hyponatraemia; rapid sodium shifts are dangerous.
Ureteric smooth muscle/alpha-1 receptor	Peristalsis and outlet tone	Tamsulosin and other alpha blockers	May help selected distal stones; dizziness and hypotension risk.

2. Practical classification of urinary medicines

Group	Examples	Main role	Major concern
UTI antibiotics	Nitrofurantoin, trimethoprim, fosfomycin, beta-lactams, fluoroquinolones	Cystitis, pyelonephritis or complicated infection	Resistance, renal dosing, allergy and tissue penetration
Loop diuretics	Furosemide	Oedema, pulmonary oedema, fluid overload	Hypovolaemia, hypokalaemia, hyponatraemia and ototoxicity
Thiazide diuretics	Hydrochlorothiazide, bendroflumethiazide	Hypertension, mild oedema, calcium stone prevention	Hyponatraemia, hypokalaemia, gout and hyperglycaemia
Potassium-sparing/aldosterone blockers	Spironolactone, eplerenone, amiloride	Heart failure, hyperaldosteronism, selected hypertension	Hyperkalaemia and renal accumulation
Renal colic medicines	NSAIDs, paracetamol, opioids	Acute stone pain	NSAID kidney injury/bleeding; opioid sedation and ileus
Alpha blockers	Tamsulosin, doxazosin	Selected distal ureteric stone passage or outlet symptoms	Postural hypotension and syncope
Bladder medicines	Oxybutynin, solifenacin, mirabegron	Overactive bladder	Anticholinergic delirium/retention or hypertension
Electrolyte/acid-base therapy	Calcium, bicarbonate, potassium binders	Selected renal/metabolic emergencies	Arrhythmia, alkalosis and rapid electrolyte shifts

3. Urinary tract infection medicines

UTI treatment depends on site, severity, pregnancy, age, renal function, catheter status and local resistance. Lower UTI (cystitis) usually causes dysuria, frequency and urgency without systemic illness. Pyelonephritis causes fever, flank pain, nausea, vomiting and systemic features. An obstructed infected kidney is a urological emergency requiring drainage as well as antibiotics.

Medicine/group	Typical role	Important safety points
Nitrofurantoin	Lower UTI when renal function and site are appropriate	Does not achieve adequate tissue levels for pyelonephritis; check renal function and pulmonary/hepatic toxicity with prolonged use.
Trimethoprim	Selected uncomplicated lower UTI	Hyperkalaemia, renal impairment, interactions with ACE inhibitors/ARBs/spironolactone and pregnancy considerations.
Fosfomycin	Selected resistant or uncomplicated lower UTI	Use local availability/resistance guidance; not a universal treatment for upper UTI.
Beta-lactams	Selected cystitis or pyelonephritis regimens	Check allergy, renal adjustment and culture results.
Fluoroquinolones	Selected complicated/upper UTI under local specialist guidance	Tendon, neurological, QT and aortic risks; reserve for appropriate indications.
Aminoglycosides	Severe resistant infection in monitored hospital care	Nephrotoxic and ototoxic; therapeutic drug monitoring is essential.

3.1 Antibiotic safety

Obtain urine culture before antibiotics when indicated and when this does not delay treatment in sepsis.
Review previous cultures, recent antibiotics, catheter history, allergies and renal function.
Complete the prescribed course; do not share leftover antibiotics or stop when symptoms first improve.
Escalate for fever with flank pain, rigors, hypotension, vomiting, pregnancy, male UTI, child UTI, catheter-associated infection or immunosuppression.

4. Pyelonephritis, urosepsis and infected obstruction

Pyelonephritis can progress to sepsis, AKI and shock. A ureteric stone or stricture can block infected urine, preventing antibiotics alone from controlling the source. Red flags include severe colic with fever, anuria/oliguria, rigors, hypotension, confusion, rising creatinine or a single functioning kidney.

Perform ABCDE, check glucose, temperature, perfusion, urine output and mental status.
Establish IV/IO access where trained, obtain cultures and lactate when available, and begin sepsis resuscitation under protocol.
Give timely broad-spectrum antibiotics authorised by the local guideline, adjusted for renal function.
Use cautious crystalloid boluses with frequent reassessment, especially in heart or kidney failure.
Arrange urgent imaging and urology review for obstruction; source control may require stent or nephrostomy.

5. Diuretics

Class	Mechanism	Uses	Adverse effects
Loop diuretic	Blocks Na-K-2Cl transport in thick ascending limb	Pulmonary oedema, heart failure, severe oedema	Hypokalaemia, hyponatraemia, hypomagnesaemia, dehydration, hypotension and ototoxicity.
Thiazide	Blocks Na-Cl transport in distal convoluted tubule	Hypertension, mild oedema and selected calcium stones	Hyponatraemia, hypokalaemia, hypercalcaemia, hyperuricaemia and glucose intolerance.
Potassium-sparing	Blocks ENaC or aldosterone receptor	Heart failure, hyperaldosteronism, resistant hypertension	Hyperkalaemia, renal impairment, endocrine adverse effects with spironolactone.
Osmotic	Raises tubular osmotic load	Specialist intracranial-pressure or renal indications	Fluid shifts, pulmonary oedema and electrolyte disturbance.

5.1 Furosemide safety

Assess blood pressure, perfusion, fluid status, lung findings, renal function, electrolytes and recent dose before giving.
In acute pulmonary oedema, nitrates and positive-pressure ventilation may be more immediately important than diuresis.
Rapid IV administration can cause ototoxicity; use the prescribed rate and monitor hearing/neurological symptoms.
Over-diuresis can precipitate AKI, hypotension and electrolyte-driven arrhythmia.

6. Acute kidney injury and nephrotoxic medicines

AKI is a sudden reduction in kidney function, often recognised by rising creatinine or reduced urine output. Causes include dehydration/low perfusion (pre-renal), obstruction (post-renal), infection, toxins, inflammation and intrinsic renal disease. Medicine management requires identifying and stopping avoidable nephrotoxins, correcting perfusion and treating the cause—not simply giving a diuretic.

Nephrotoxin/risk	Potential injury	Safety response
NSAIDs	Reduce renal prostaglandin-mediated perfusion	Avoid in dehydration, shock, CKD or AKI; use safer analgesic plan.
ACE inhibitor/ARB	Reduces intraglomerular pressure; can worsen AKI during hypovolaemia	Medication reconciliation and clinician review during acute illness.
Aminoglycosides/vancomycin	Tubular injury and accumulation	Culture-directed use, renal dosing and drug-level monitoring.
Contrast media	Risk in vulnerable patients	Assess AKI/CKD, dehydration and nephrotoxins; follow imaging protocol.
Herbal/traditional remedies	Unknown nephrotoxic ingredients or contamination	Ask non-judgementally and document all products.

7. Chronic kidney disease and renal dose adjustment

CKD changes clearance, protein binding, acid–base balance, erythropoiesis, bone-mineral metabolism and cardiovascular risk. A “normal” creatinine can be misleading in a small or frail person with low muscle mass. Dose decisions should use the prescribed renal function estimate and specialist guidance.

Renally cleared antibiotics, opioids, gabapentinoids, insulin, anticoagulants and sedatives may need lower doses or longer intervals.
Accumulation can present as confusion, excessive sleepiness, ataxia, respiratory depression, bleeding or severe nausea.
Ask whether the patient receives haemodialysis, peritoneal dialysis or a transplant; timing around dialysis changes medicine removal.
Avoid abrupt fluid loading in anuric patients; pulmonary oedema can develop rapidly.

8. Electrolyte and acid–base emergencies

Emergency	Clinical clues	Medicine/support principle
Hyperkalaemia	Weakness, paraesthesia, bradycardia, peaked T waves, widened QRS	Cardiac monitoring; IV calcium stabilises myocardium, while insulin/glucose and other therapies shift or remove potassium under protocol.
Hypokalaemia	Weakness, cramps, ileus, U waves and arrhythmia	Replace potassium carefully with ECG/renal monitoring; treat magnesium deficiency and cause.
Hyponatraemia	Headache, confusion, seizures, nausea	Identify acute/severe symptoms; hypertonic saline is specialist-controlled because rapid correction can injure the brain.
Metabolic acidosis	Deep breathing, confusion, hypotension	Treat cause such as sepsis, DKA or renal failure; bicarbonate is selective, not routine.
Uraemia	Confusion, pericarditis, pruritus, nausea, bleeding tendency	Urgent renal review; dialysis may be required for refractory complications.

9. Alpha blockers and renal colic

NICE recommends an NSAID as first-line analgesia for suspected renal colic when not contraindicated; IV paracetamol is an alternative when NSAIDs are unsuitable or insufficient, with opioids considered when necessary. Alpha blockers may be considered for selected distal ureteric stones under clinician direction.

Check pregnancy, renal function, GI bleeding, anticoagulants, asthma and allergy before NSAIDs.
Alpha blockers may cause postural hypotension, dizziness and syncope; counsel the patient to rise slowly.
Unrelenting pain, fever, anuria, solitary kidney or rising creatinine requires urgent urological review—not repeated outpatient analgesia.

10. Bladder and urinary-symptom medicines

Class	Examples	Role	Emergency precautions
Antimuscarinics	Oxybutynin, solifenacin, tolterodine	Overactive bladder and urgency	Dry mouth, constipation, blurred vision, delirium and urinary retention; avoid in obstruction or high anticholinergic burden.
β3 agonist	Mirabegron	Relaxes detrusor muscle	May raise BP; review severe hypertension and interactions.
Urinary analgesic	Phenazopyridine where available	Short-term dysuria symptom relief	Does not treat infection; urine discoloration and renal/hepatic cautions.
Desmopressin	V2 agonist reduces urine output	Diabetes insipidus, nocturnal enuresis and selected bleeding disorders	Water intoxication and hyponatraemia; fluid restriction and sodium monitoring matter.

11. Dialysis and medicine considerations

Ask the patient’s dialysis schedule, vascular access type and last session; missed dialysis can cause fluid overload, hyperkalaemia and uraemia.
Never take blood pressure or insert IV lines in a functioning arteriovenous fistula arm unless the renal team authorises it.
Some medicines are removed by dialysis, some are not, and timing may be deliberately post-dialysis.
Patients may be anticoagulated during dialysis; bleeding and access-site complications require careful pressure and documentation.
Urgent transfer is required for pulmonary oedema, severe hyperkalaemia/ECG changes, pericarditis, severe acidosis or altered consciousness.

12. Clinical scenarios

Scenario 1: Pyelonephritis with sepsis

A febrile patient has flank pain, rigors, tachycardia and hypotension. Perform ABCDE, obtain access and cultures where feasible, start authorised sepsis fluids/antibiotics with renal adjustment and transfer urgently. Ask about stones because obstruction changes the required source control.

Scenario 2: Infected obstructed kidney

A patient with renal colic develops fever and anuria. Do not treat as simple pain. Give monitored support, avoid delaying antibiotics and arrange emergency urology assessment for drainage.

Scenario 3: AKI after vomiting

A dehydrated patient has taken ibuprofen and an ACE inhibitor during gastroenteritis. Review nephrotoxins, restore perfusion cautiously, monitor urine output/electrolytes and seek clinician review before further doses.

Scenario 4: Hyperkalaemia

A dialysis patient has weakness and a wide QRS. Place on ECG monitoring, call advanced help and follow the hyperkalaemia protocol. Calcium protects the myocardium but does not remove potassium; insulin/glucose and definitive dialysis may be required.

Scenario 5: Renal colic in pregnancy

A pregnant patient has flank pain and haematuria. Avoid casual NSAID use, assess for infection/obstruction and arrange obstetric/urological advice for analgesia and imaging.

Scenario 6: Diuretic-related collapse

A patient on high-dose furosemide is dizzy with low BP and cramps. Check fluid status, ECG and electrolytes; do not automatically give another diuretic for ankle swelling.

13. Monitoring and documentation

Record urine output, fluid intake/losses, weight when available, BP, pulse, perfusion, lung findings, mental status, medication/last dose, allergy, renal function and ECG. For antibiotics document culture, dose, time and response. For diuretics document urine response and electrolytes. Handover the last dialysis session, access site, obstruction risk and any nephrotoxins.

14. Revision questions

Explain how the kidneys alter medicine clearance.
Differentiate cystitis, pyelonephritis and urosepsis.
Why is an infected obstructed kidney a source-control emergency?
List the common nephrotoxic medicines and risk situations.
Compare loop, thiazide and potassium-sparing diuretics.
What are the danger signs of furosemide over-diuresis?
Why can trimethoprim cause hyperkalaemia?
Explain first-line pharmacological care of renal colic.
When may alpha blockers be considered?
How should dialysis access be protected?
List signs of hyperkalaemia requiring ECG monitoring.
Why is rapid correction of hyponatraemia dangerous?
What are the major cautions for NSAIDs in renal patients?
Compare antimuscarinic bladder medicines with mirabegron.
Which findings suggest AKI?
How does renal failure alter opioid and gabapentinoid safety?
What information is essential in a urinary medicine handover?
Write a safe plan for a patient with UTI, hypotension and reduced urine output.

15. Key takeaways

Renal patients need medicine reconciliation, renal-dose review, electrolyte monitoring and careful fluid assessment.
Fever plus obstruction, anuria or shock is an emergency; antibiotics alone may not control the source.
NSAIDs help renal colic but can worsen AKI, bleeding and heart failure.
Diuretics remove fluid but do not automatically improve kidney function; over-diuresis causes shock and electrolyte arrhythmia.
Hyperkalaemia, severe acidosis, pulmonary oedema and uraemic complications require urgent monitored care and possible dialysis.
Document urine output, last doses, last dialysis, access site, cultures and every medicine/fluid given.

16. Recommended references for further study

Clinical note: This page supports EMT learning and revision. It does not replace an authorised prescription, local emergency protocol, senior supervision or patient-specific advice. In a deteriorating patient, stabilise ABCDE, call for advanced help and transfer urgently.