Alprostadil

Alprostadil is a synthetic form of prostaglandin E1 (PGE1), a naturally occurring signaling lipid that relaxes smooth muscle and dilates blood vessels. Unlike many compounds cataloged here, alprostadil is an approved medicine used in defined clinical settings.

Its two best-known approved roles are in the treatment of erectile dysfunction and in newborn medicine, where it is used to keep a specific fetal blood vessel open in certain heart conditions. Because it works by dilating blood vessels, most of its effects and risks trace back to that vasodilatory action.

Alprostadil is a prostaglandin that acts on prostaglandin receptors on smooth muscle. The downstream effect is relaxation of vascular and other smooth muscle, which widens blood vessels and increases blood flow. High-level themes include:

• Relaxing smooth muscle in blood-vessel walls, producing vasodilation and increased local blood flow.

• In erectile tissue, promoting the increased blood flow involved in achieving an erection.

• In the newborn setting, maintaining the openness of the ductus arteriosus, a vessel that normally closes after birth.

Because this vasodilatory mechanism is systemic in principle, it also explains effects such as lowered blood pressure when the drug reaches the broader circulation.

Alprostadil is an approved medicine, and its use contexts are well defined rather than experimental:

• Erectile dysfunction: Approved formulations are used to produce an erection through local administration.

• Neonatal use: It is used in newborns with certain ductal-dependent congenital heart defects to keep the ductus arteriosus open until definitive treatment.

These are established, regulated indications with defined labeling, in contrast to speculative or off-label uses. Alprostadil should be used within its approved contexts under appropriate medical care.

Alprostadil (prostaglandin E1) is a vasodilator and is not a specifically named substance on the World Anti-Doping Agency (WADA) Prohibited List. It is not a hormone, anabolic agent, or recognized performance enhancer.

As always, athletes remain responsible for any medicine they use and should confirm current status and, where relevant, therapeutic use requirements with the appropriate authority. Not being specifically listed does not remove an athlete's general responsibility to verify what they take.

Commonly discussed effects relate to its site of use and its blood-vessel action, including local injection-site or application-site reactions and pain in the treated area. A specific and important concern in the erectile-dysfunction setting is a prolonged, painful erection (priapism), which requires prompt medical attention.

Because it dilates vessels systemically in principle, alprostadil can lower blood pressure, and in the newborn setting effects such as apnea are recognized and monitored. These considerations are why it is administered within structured clinical oversight.

Alprostadil is a short-acting prostaglandin, and its pharmacology reflects rapid local action followed by extensive metabolism, which is part of why some uses rely on continuous or local administration.

Conceptually, its use is shaped by the goal (local blood flow versus maintaining a specific vessel's openness), the route appropriate to that goal, and its short duration of action. These are clinical decisions, not self-directed ones.

Alprostadil is the same molecule in every product; what changes is how it is delivered, and the route is chosen entirely to keep a systemic vasodilator from acting systemically.

• Intracavernosal injection — Caverject and Caverject Impulse (Pfizer) and Edex (Endo), supplied as lyophilized powder for reconstitution; Caverject comes in 20 and 40 mcg single-dose vials (Caverject prescribing information).

• Intraurethral pellet — MUSE, a micro-suppository 1.4 mm across and 3 or 6 mm long, seated in the tip of an applicator and delivered into the urethra after urination, at doses from 125 to 1000 mcg (MUSE prescribing information). Needle-free, but dosed roughly 10 to 25 times higher than the injected route to reach the same tissue.

• Continuous intravenous infusion — Prostin VR Pediatric, 500 micrograms of alprostadil in 1 mL of dehydrated alcohol, diluted and run into a large vein or an umbilical artery catheter (Prostin VR prescribing information). Generic alprostadil injection concentrate serves the same purpose.

Why infusion rather than a dose? Roughly 80% of circulating alprostadil is metabolised in a single pass through the lungs, primarily by beta- and omega-oxidation, with metabolites cleared renally and excretion essentially complete within 24 hours. A prostaglandin that disappears that fast cannot be given as an intermittent dose when the goal is to hold a vessel open for days.

Combination is a live hazard rather than a strategy here. The Caverject label notes that safety and efficacy of intracavernosal alprostadil combined with other vasoactive agents have not been established, and that the risks of prolonged erection, priapism, and hypotension may be increased.

Unlike many experimental peptides, alprostadil has an established evidence base supporting its approved indications, with well-characterized effects on blood flow, erectile function, and ductal patency. This is reflected in its regulatory approval and defined labeling.

Research also touches on related vascular applications of prostaglandin E1. Even with an established core evidence base, use should remain grounded in approved indications and clinical judgment rather than extrapolation.

For deeper dives on this medicine, see:

• Alprostadil benefits and areas of interest
• Alprostadil side effects and safety context
• Alprostadil dosing concepts (educational)
• Alprostadil research and evidence overview

Is alprostadil a peptide? No. Alprostadil is prostaglandin E1, a 20-carbon eicosanoid — a lipid — with the formula C20H34O5 and a molecular weight of about 354.5, containing no amino acids at all (PubChem CID 5280723). It appears in peptide catalogs because it shares a market with PT-141 and other sexual-function compounds, not because it shares any chemistry with them.

What is alprostadil approved for? Two very different things. Caverject and MUSE are indicated for the treatment of erectile dysfunction, with Caverject also approved as an adjunct in diagnostic testing. Prostin VR Pediatric is indicated for palliative therapy to temporarily maintain patency of the ductus arteriosus in neonates with ductal-dependent congenital heart defects — pulmonary atresia, tricuspid atresia, tetralogy of Fallot, interrupted aortic arch, coarctation, transposition of the great vessels — until corrective surgery can be performed (Prostin VR prescribing information).

How does alprostadil differ from Viagra or Cialis? Alprostadil does the work itself; PDE5 inhibitors only amplify a signal the body has already started. Alprostadil binds prostaglandin receptors and raises intracellular cAMP through adenylate cyclase, directly relaxing trabecular smooth muscle and dilating cavernosal arteries. Sildenafil, by contrast, "has no direct relaxant effect on isolated human corpus cavernosum" and works only by blocking the breakdown of cGMP produced when sexual stimulation releases nitric oxide — the label states that at recommended doses it has no effect in the absence of sexual stimulation (Viagra prescribing information). That is the practical reason alprostadil is considered when oral agents have failed.

How likely is priapism? Uncommon but consequential. In the Caverject clinical program of 1,861 patients treated for up to 18 months, prolonged erection lasting 4 to 6 hours occurred in 4%, and priapism — an erection lasting more than 6 hours — in 0.4%. The label instructs that an erection persisting beyond 4 hours requires immediate medical assistance, because untreated priapism can cause penile tissue damage and permanent loss of potency. Penile fibrosis was reported in 3% overall, rising to 7.8% in one 18-month self-injection study.

How well does the urethral form work? Modestly, and the trial design matters. Across two identical placebo-controlled studies, 1,511 men began in-clinic dose titration and 996 (66%) achieved an erection sufficient for intercourse and were randomised; among those responders, 65% had at least one successful intercourse at home versus 19% on placebo, and erections adequate for penetration lasted 16 minutes on drug versus 6 on placebo (MUSE prescribing information). The label is explicit that these are response rates only in men who were successfully titrated — a third never got that far, often because of penile pain.

Why does a newborn drug carry an apnea warning? Because it is the most common serious effect at the doses used. Prostin VR's boxed warning states that apnea occurs in about 10 to 12% of neonates with congenital heart defects treated with it, most often in those weighing under 2 kg at birth and usually within the first hour of infusion — which is why it is only given where ventilatory assistance is immediately available. Fever (about 14%), flushing (about 10%), bradycardia (about 7%), and seizures (about 4%) are also reported.

Is alprostadil banned in sport? It is not named on the WADA Prohibited List. It is a vasodilator rather than a hormone, anabolic agent, or metabolic modulator, and it is not a recognised performance enhancer. Athletes remain responsible for verifying the status of anything they take, and note that the intravenous infusion route intersects with the separate M2.2 restriction on infusion volume.