Alprostadil exerts its effects by mimicking the action of prostaglandin E1 (PGE1), a naturally occurring substance in the body. The mechanism of action involves:

1. Vasodilation:
   • Alprostadil binds to prostaglandin receptors on smooth muscle cells, activating adenylate cyclase.
   • This increases intracellular cyclic adenosine monophosphate (cAMP) levels, leading to relaxation of smooth muscles and dilation of blood vessels.
2. Erectile Dysfunction:
   • In the treatment of ED, alprostadil injected into the corpora cavernosa or administered intraurethrally causes localized vasodilation, increasing blood flow to the penis and facilitating an erection.
3. Ductus Arteriosus Patency:
   • In neonates, alprostadil maintains the patency of the ductus arteriosus, a blood vessel that connects the pulmonary artery to the aorta, allowing blood to bypass the lungs in certain congenital heart defects.

Alprostadil is approved for the following conditions:

1. Erectile Dysfunction (ED):
   • Treatment of ED in men who have difficulty achieving or maintaining an erection. It is available in three formulations:
     • Intracavernosal Injection: Injected directly into the penis.
     • Intraurethral Suppository: Inserted into the urethra.
     • Topical Cream: Applied to the tip of the penis (less commonly used).
2. Maintaining Ductus Arteriosus Patency:
   • Used in neonates with congenital heart defects (e.g., ductal-dependent cyanotic heart disease) to maintain the patency of the ductus arteriosus until surgical correction can be performed.

The dosage of alprostadil varies depending on the indication and formulation. Below are general guidelines:

1. Erectile Dysfunction:
   • Intracavernosal Injection:
     • Initial Dose: 2.5–5 mcg injected into the corpora cavernosa.
     • Titration: Adjust the dose in increments of 5–10 mcg based on response, up to a maximum of 60 mcg per injection.
     • Frequency: Use no more than once daily and no more than three times per week.
   • Intraurethral Suppository:
     • Dose: 125–1000 mcg inserted into the urethra.
     • Frequency: Use no more than once daily.
   • Topical Cream:
     • Dose: Apply a measured dose to the tip of the penis as directed.
     • Frequency: Use no more than once daily.
2. Maintaining Ductus Arteriosus Patency:
   • Neonates:
     • Initial Dose: 0.05–0.1 mcg/kg/min by continuous intravenous infusion.
     • Titration: Adjust the dose based on response, up to a maximum of 0.4 mcg/kg/min.

Alprostadil is generally well-tolerated, but some side effects may occur. These include:

1. Common Side Effects:
   • Intracavernosal Injection:
     • Penile pain
     • Prolonged erection (priapism)
     • Penile fibrosis (scarring)
   • Intraurethral Suppository:
     • Urethral pain or burning
     • Minor urethral bleeding
   • Topical Cream:
     • Local irritation or redness
2. Less Common Side Effects:
   • Dizziness
   • Headache
   • Hypotension (low blood pressure)
3. Rare but Serious Side Effects:
   • Priapism: Prolonged and painful erection lasting more than 4 hours. This is a medical emergency and requires immediate treatment.
   • Severe Hypotension: Especially in neonates receiving intravenous alprostadil.
   • Apnea: Respiratory depression in neonates.

1. Contraindications:
   • Hypersensitivity to alprostadil or any component of the formulation.
   • Conditions that predispose to priapism (e.g., sickle cell anemia, multiple myeloma).
   • Anatomical deformities of the penis (e.g., Peyronie’s disease).
2. Warnings:
   • Priapism: Patients should seek immediate medical attention if an erection lasts longer than 4 hours.
   • Penile Fibrosis: Regular monitoring for signs of penile scarring or curvature.
   • Neonates: Monitor for apnea and hypotension during intravenous infusion.
3. Monitoring:
   • Regular assessment of erectile function and penile health in patients using alprostadil for ED.
   • Continuous monitoring of vital signs in neonates receiving intravenous alprostadil.

Alprostadil has a low potential for drug interactions due to its localized action. However, the following should be considered:

1. Antihypertensive Medications: May cause additive hypotensive effects.
2. Anticoagulants (e.g., warfarin): Increased risk of bleeding with intraurethral suppository use.

Other Vasodilators: May enhance the hypotensive effects of alprostadil

Alprostadil is available under its generic name as well as brand names. Some common formulations include:

• Generic Name: Alprostadil
• Brand Names:
  • Intracavernosal Injection: Caverject, Edex.
  • Intraurethral Suppository: MUSE (Medicated Urethral System for Erection).
  • Topical Cream: Vitaros (available in some regions).