Erectile dysfunction medications

Erectile Dysfunction Medications

Erectile Dysfunction

Erectile dysfunction, ED is the inability of the male to attain and maintain an erection sufficient to permit satisfactory sexual intercourse.

Penile erectile dysfunction is a condition in which the corpus cavernosum does not fill with blood to allow for penile erection. This can result from the aging process and in vascular and neurological conditions.

So, what is impotence?

Impotence, a term often used synonymously with ED, many involve a total inability to achieve erection, an inconsistent ability to achieve or ability to sustain only brief erections.

Physiology of an Erection

This begins with stimulus such as sight and touch. This stimulates the parasympathetic nervous division that transmits nerve impulses to the erectile tissue of the penis (corpus carvernosum). The nerve endings release nitric oxide(NO) which binds on muscle cells in the penis leading to generation of cyclic GMP (Cyclic Guanosine monophosphate) which relaxes the muscle cells in the corpus cavernosum leading to creation of larger intracellular spaces and sinusoids. More blood flows into the erectile tissues, the tissue expands compresses the veins leaving the penis, thus increased blood volume in the organ and one erects.

      Erection is continuously maintained during sexual intercourse by the release of NO, and prostaglandin E1 (PGE1).

Termination of erection( Detumescence ) is brought about by 2 events i.e.

  • Activity of enzyme phosphodiesterase type 5 enzyme (PDE-5) which catalyzes the breakdown of GMP into inactive form.
  • Stimulation of sympathetic nervous division to bring about the contraction of the penile muscles terminating ejaculation.


Pharmacology application of the above;

  • Erection relies on the penile blood flow thus an event that interferes with penile blood flow results into penile dysfunction.
  • Any factor which interferes with neuro-transmitters such as acetylcholine may end with Erectile Dysfunction.
  • Psychological factors e.g. stress may as well interfere initiation of erection.

Classification of Erectile Dysfunction.

Primary Erectile Dysfunction; is where a man has never  been able to attain and maintain an erection for sexual intercourse

Secondary Erectile Dysfunction: is where impotence occurs in a man who has past history of satisfactory sexual performance.

Causes of Erectile Dysfunction

  • Erectile Dysfunction mainly occurs past middle age and is common after the age of 65 years.

A variety of vascular, Neurological, hormonal or endocrinal, pharmacological or psychological and genetic causes may underly the disorder, i.e.

  • Vascular diseases: Blood supply to the penis can become blocked or narrowed as a result of vascular disease such as atherosclerosis (hardening of the arteries).
  • Neurological disorders (such as multiple sclerosis): Nerves that send impulses to the penis can become damaged from stroke, diabetes, or other causes.
  • Psychological states: These include stress, depression, lack of stimulus from the brain and performance anxiety.
  • Trauma: An injury could contribute to symptoms of Erectile Dysfunction.
  • Cancer treatments;  near the pelvis can affect the penis’ functionality.
    Surgery and or radiation for cancers in the lower abdomen or pelvis can cause Erectile dysfunction. Treating prostate, colon-rectal or bladder cancer often leaves men with Erectile dysfunction.
  • Drugs;  used to treat other health problems can negatively impact erections such as Cimetidine (Tagamet), Ranitidine (Zantac)

Classification of Drugs used to treat Erectile Dysfunction.

There are divided into 4 groups;

  • Central inhibitors
  • Peripheral inhibitors
  • Central conditioners
  • Peripheral conditioners

PDE 5 Inhibitors/Peripheral Inhibitors.

These are agents which act in the penile tissue to maintain the environment of erection. They include phosphodiesterase-5 inhibitors e.g. sildenafil, tadalafil, and vardenafil are selective PDE-5 inhibitors developed drugs in the past decade and found effective in a majority of patients with Erectile Dysfunction.


 It is an orally active drug


Therapeutic– ED agent, vasodilator

Pharmacological– phosphodiesterase type 5 inhibitor

Brand names:
  • Kamagra
  • Penegra
  • viagra
  • Caverta
  • Edegra 25, 50, 100mg tablets
  • Erectile Dysfunction
  • Pulmonary Hypertension.
Mechanism of action;

 Sildenafil acts by selectively inhibiting an enzyme phosphodiesterase-5 and enhancing nitric oxide action in corpus cavernosum thus preventing the breakdown of GMP produces smooth muscle relaxation of the corpus cavernosum which in turn promotes increased blood flow and subsequent erection hence sex intercourse and exercise tolerance is improved but it has no effect on penile (swelling) tumescence in the absence of sexual activity. It doesn’t cause priapism in most patient.


  It is recommended in the dose of

  • 50mg for men less than 65 years,
  • elderly 25mg if not effective then 100mg 1 hour by intercourse.

Duration and degree of penile erection is increased in 74-82% of men with Erectile Dysfunction including diabetic Neuropathy cases.

However, Sildenafil is effective in men who have lost libido or when ED is due to spinal cord injury or damaged Nervic eregantis since Nitric Oxide is an important regulator of pulmonary vascular resistance, PDE-5 inhibitor lower pulmonary circulation than vardenafil and is only PDE-5 inhibitor shown to improve arterial   oxygenation in pulmonary Hypertension. It has now become the drug of choice for this condition

N.B.; it should be given once a day.  

Adverse effects/ side effects:

These are mainly due to preservation of nitric oxide which causes vasodilatation in the brain.

  • Dizziness and headache
  • Nasal congestion
  • Hypotension and palpitation
  • Loose emotion
  • A feeling of dependency/ addiction
  • Flushing
  • Tachycardia
  • Muscle pain
  • Diarrhoea
  • Sildenafil in addiction, weakly inhibits the isoenzyme PDE-5 which is involved in photoreceptor transduction in the retina. As such impairment of colour vision especially, blue-green discrimination occurs in some recipients.
  • Hormones and related drug neuropathy among users of PDE-5 inhibitors have be reported.
  • In patients with coronary heart diseases.
  • Those taking nitrates. Though sildenafil remains effective for less than 2hours, it is advised that nitrates should be avoided for 24hours
  • Presence of liver or kidney disorder
  • Peptic ulcer, bleeding disorder
  • Patients of leukemia, sickle cell anemia, myocardial infarction etc.
Drug interactions:
  •  Sildenafil markedly potentiates the vasodilator action of nitrates, precipitates fall in Blood Pressure and myocardial infarction may occur.
  • Inhibitors of CYP3A4 like erythromycin, Ketoconazote, cemetidine may potentiate its action i.e. may increase Sildenafil plasma concentration.
  • Vitamin k antagonist may increase the risk of bleeding.
  • Concomitant use with alpha- blockers may lead to hypotension.

N.B: men even without Erectile Dysfunction are going for it to enhance sexual satisfaction.

Nursing implications:
  • Determine Erectile Dysfunction before administration.
  • Monitor hemodynamic parameters and exercise before and after therapy
Patient/ family teaching:
  • Instruct the patient to take drugs at least 1 hour before sexual activity
  • Not more than once a day.
  • Instruct the patient that sexual stimulation is required for erection to occur.
  • Advise the patient that the drug is not indicated for women.
  • Advise the patient not to concurrently take the drug with nitrates or alpha-adrenergic blockers
  • Instruct the patient if chest pain occurs after taking the drug to report to the PHC practioners immediately.
  • Advise the patient to avoid excess alcohol intake in combination with PDE-5 since it can increase the risk of orthostatic hypotension
  Brand names;
  • Megalis,
  • Tadarich,
  • Tadalis,
  • Cialis and Apcalis 10, 20mg tablets

            It is a more potent and longer acting congener of Sildenafil, duration of action is 24-36 hours. It is claimed to act faster, though peak plasma levels are attained between 30-120minutes.

  • Erectile Dysfunction
Mechanism of action
  • As for Sildenafil

Side effects, risks, contraindications and drug interactions are similar to Sildenafil

  • Because of its longer lasting action, nitrates are contraindicated for 36-48hours after Tadalafil.
  • Due to its lower affinity for PDE-6, visual disturbances occur less frequently
  •  10mg o.d. at least 30minutes before sexual intercourse (max 20mg)

Peripheral Initiators of Erection

They include Alprostadil administered intra cavernously (injected) directly into the corpus cavernosum using a fine needle or introduced into the urethra as a small pellet, produces erection in few hours to permit intercourse  .  It is more used in patients taking anti-hypertensive drugs, those with cardiac diseases e.g Coronary artery disease and patients who do not respond to PDE-5 inhibitors.

Mode of Action

It is a prostaglandin E1 analog thus relaxes the penile muscles bringing about erection.

  1.  Presence of any anatomical obstruction or condition that might predispose to priapism. The risk could be exacerbated by these drugs.
  2.  Penile implants.
  3.  Bleeding disorders, CV diseases, optic neuropathy, severe hepatic and renal disorders.
Adverse effects
  • Priapism
  • Thrombo-embolism
  • Local tenderness
  • Penile fibrosis

Central initiators:

 These initiate neuronal path ways for erection e.g.

  • Apomorphine administered orally
Mechanism of action:

Apomorphine is a dopamine agonist  which acts centrally to stimulate an erectile neuronal path way.

It is also for known for Parkinsonism and induction of vomiting thus rarely used for this indication

Adverse effect:
  • Nausea and vomiting
  • Head ache and dizziness
  • Decreased milk production if taken by lactating mothers for another use

Central conditioners:

These provide a central mood condition of erection. They include;

(a). Trazodone which is a CNS anti-depressant due to massive adverse effects

(b). Androgens: e.g. testosterone

Click here to read more about Androgens.

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