Alprostadil
Alprostadil is synthetic prostaglandin E1 used for erectile dysfunction as an intracavernosal injection (Caverject) or intraurethral pellet (MUSE). Unlike oral PDE5 inhibitors it acts locally to relax cavernosal smooth muscle independent of nerve signalling, so it works even when PDE5 inhibitors fail — but at the cost of an invasive route and a real risk of prolonged erection.
01 Overview
Alprostadil is prostaglandin E1, which raises intracellular cyclic AMP in cavernosal smooth muscle, producing relaxation and erection independent of nitric-oxide signalling. Because it bypasses the neural/NO pathway, it is effective in men who do not respond to oral PDE5 inhibitors, including some with nerve damage after prostatectomy. It is delivered directly — injected into the corpus cavernosum or inserted as a urethral pellet.
The trade-off is the invasive administration and a genuine risk of priapism (a prolonged, painful erection lasting over four hours) which is a urological emergency, as well as penile pain and, with repeated injections, fibrosis. It is a legitimate prescription therapy rather than a lifestyle drug, and self-administration requires proper training and a plan for priapism.
02 Mechanism
Synthetic prostaglandin E1: raises cAMP in cavernosal smooth muscle, producing NO-independent vasodilation and erection.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Intracavernosal injection | 2.5–20 mcg | IM | Injected into the corpus cavernosum; titrated under supervision. (Route is intracavernosal, closest enum INTRAMUSCULAR.) |
| Intraurethral pellet | 125–1000 mcg | Rectal | MUSE urethral suppository; higher doses reflect lower local bioavailability. (Route is intraurethral, closest enum RECTAL.) |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Erection independent of PDE5 pathwayProduces erection even in men who fail oral PDE5 inhibitors, including post-prostatectomy nerve damage. | ~70% response | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Penile painPain at the injection site or in the penis is frequent, especially with the urethral pellet. | Moderate | Common | Clinical | |
| Penile fibrosis / Peyronie-like changesFibrous nodules or curvature can develop with long-term repeated injection. | Moderate | Uncommon with repeated use | Clinical | |
| Priapism (prolonged erection)An erection lasting over 4 hours is a urological emergency that can cause permanent tissue damage. | Severe | Uncommon but urgent | Clinical |