1. Clinical Overview
Alprostadil is a synthetic, naturally occurring prostaglandin E1 (PGE1) analogue. It is a potent vasodilator and platelet aggregation inhibitor. In the Indian market, the 500mcg strength is primarily formulated as an injection for intracavernosal use in the diagnosis and treatment of erectile dysfunction (ED) of vasculogenic, neurogenic, or psychogenic origin. It is also used as an intravenous infusion for maintaining patency of the ductus arteriosus in neonates with congenital heart defects awaiting surgery.
| Onset | Duration | Bioavailability |
|---|---|---|
| Intracavernosal: 5-10 minutes. Intravenous: Within minutes. | Intracavernosal: Erection typically lasts 30-60 minutes. Intravenous: Hemodynamic effects are transient, lasting only while infusion continues. | Not applicable for injectable forms; systemic bioavailability is 100% upon injection. |
2. Mechanism of Action
Alprostadil binds to specific prostaglandin E1 receptors on vascular and cavernosal smooth muscle cells. This activates adenylate cyclase, increasing intracellular cyclic adenosine monophosphate (cAMP). Elevated cAMP leads to decreased intracellular calcium, resulting in smooth muscle relaxation (vasodilation). In the penis, this relaxes trabecular smooth muscle and dilates cavernosal and helicine arteries, increasing blood flow, trapping blood, and causing erection. Systemically, it causes vasodilation and inhibits platelet aggregation.
3. Indications & Uses
- Erectile Dysfunction (Vasculogenic, Neurogenic, Psychogenic) - Intracavernosal injection.
- Maintaining patency of Ductus Arteriosus in neonates with ductal-dependent congenital heart disease (e.g., pulmonary atresia, critical coarctation of aorta) - Intravenous infusion.
4. Dosage & Administration
Adult Dosage: Erectile Dysfunction (Intracavernosal): Initial dose: 2.5 mcg. Titrate upwards in 2.5-5 mcg increments to a minimum effective dose that produces an erection not exceeding 1 hour. Maximum single dose: 60 mcg. Dosing frequency should not exceed once daily and 3 times per week.
Administration: INTRACAVERNOSAL: Use a U-100 insulin syringe (0.5 or 1 mL). Administer at the lateral aspect of the proximal third of the penis, alternating sides. Use aseptic technique. Apply pressure to site for 5 minutes. Patient must be trained by a healthcare professional. INTRAVENOUS (Neonates): Administer via a large vein or umbilical artery catheter. Use an infusion pump. Reconstitute as per manufacturer's instructions.
5. Side Effects
Common side effects may include:
- Penile Pain (up to 37% of patients).
- Local injection site reactions (hematoma, bleeding, ecchymosis).
- Prolonged erection (>1 hour, <4 hours).
- Penile Fibrosis (nodules, plaques) with chronic use.
- Flushing.
- Headache.
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Anticoagulants (Warfarin, NOACs) / Antiplatelets (Aspirin, Clopidogrel) | Increased risk of bleeding and hematoma at injection site. | Moderate |
| Antihypertensives | Additive hypotensive effect. | Moderate |
| Other Vasodilators (e.g., Nitrates, PDE5 inhibitors like Sildenafil) | Profound hypotension. CONTRAINDICATED for concomitant use with intracavernosal Alprostadil. | High |
| Monoamine Oxidase Inhibitors (MAOIs) | Potential for exaggerated hypotensive response. | Moderate |
7. Patient Counselling
- DO receive thorough training from your doctor/nurse on proper injection technique, site rotation, and asepsis.
- DO use the correct syringe (U-100 insulin) and needle.
- DO apply firm pressure to the injection site for at least 5 minutes to prevent bleeding/bruising.
- DO seek immediate medical help if an erection lasts more than 4 hours.
- DONT inject more than once in 24 hours or more than 3 times a week.
- DONT share your medication or syringes.
- DONT use if the solution is discolored or contains particles.
8. Toxicology & Storage
Overdose: INTRACAVERNOSAL: Priapism (painful, prolonged erection >4 hours). Systemic symptoms (if large dose enters circulation): Severe hypotension, flushing, dizziness, syncope, tachycardia. NEONATAL IV: Apnea, bradycardia, hypotension, hyperpyrexia, seizures.
Storage: Store unopened vials/ampoules in a refrigerator between 2°C to 8°C. Do not freeze. Protect from light. Once reconstituted (if required), use immediately. For some pre-filled syringes, follow specific manufacturer's instructions regarding storage after first use. Keep out of reach of children.