Prostaglandin E1 Injection: Uses and Side Effects

Prostaglandin E1 (PGE1), sold under the generic name alprostadil, is an injectable drug with two very different medical lives. In urology, it is injected directly into the penis to treat erectile dysfunction, and it remains one of the most effective options when oral medications fail. In neonatal medicine, it is given intravenously to newborns with certain heart defects to keep a critical blood vessel open until surgery can be performed. A third, less common use involves intravenous infusion for severe peripheral artery disease in the legs. Each application carries a distinct set of side effects, and the drug’s behavior in the body helps explain why.

How PGE1 Works in the Body

PGE1 is a naturally occurring fatty-acid molecule that relaxes smooth muscle in blood vessel walls. When injected, it widens small arteries and improves blood flow to the surrounding tissue. Research in animal models has shown that PGE1 can reverse constriction in arterioles and small arteries with diameters as small as 10 to 50 microns, making it a potent vasodilator at the microvascular level.¹ In the penis specifically, the relaxation depends mainly on a signaling pathway involving cAMP, a molecule that tells smooth muscle cells to loosen up. Blocking this pathway weakens the drug’s effect, while the nitric-oxide pathway that oral erectile dysfunction pills rely on plays little direct role in PGE1’s action.²

One important feature of PGE1 is that the body breaks it down extremely fast. When it enters the bloodstream, the lungs metabolize nearly all of it in a single pass. Pharmacokinetic studies in animals found that measuring intact PGE1 in the blood is practically impossible because it is converted to inactive breakdown products almost instantly.³ When injected into the penis, some of the drug acts locally before the rest is swept into general circulation and quickly deactivated.⁴ This rapid clearance is a double-edged sword: it limits how long systemic side effects last, but it also means the drug’s window of action is relatively short.

Treating Erectile Dysfunction

Intracavernosal injection of alprostadil is primarily used for erectile dysfunction when oral pills like sildenafil or tadalafil don’t work well enough. This includes men who have had nerve-sparing or non-nerve-sparing radical prostatectomy for prostate cancer, men with diabetes-related vascular damage, and those with other organic causes of ED.⁵

The clinical evidence supporting this use is strong. In a large study published in the New England Journal of Medicine, 296 men were tested with varying doses. All doses outperformed placebo, with a clear dose-response relationship. In a separate six-month home-injection phase involving 683 men, participants reported being able to have sexual activity after about 94% of injections. Both the men and their partners rated the experience as satisfactory roughly 87% of the time.⁶ Among diabetic men specifically, an effective home dose was established for 94% of participants, and a satisfactory erectile response occurred after 99% of injections, with a median dose of 20 micrograms.⁷

Dose requirements vary depending on the underlying cause. In the New England Journal of Medicine trial, men with psychogenic erectile dysfunction tended to respond to lower doses than those with vascular causes. The minimum effective dose was 2 micrograms or less in 38% of men with psychogenic causes, compared to 20% of those with vascular causes.⁶ Before patients begin self-injecting at home, dose titration happens in a clinical office with monitoring, to find the right amount and ensure the patient can handle the injection technique safely.⁸

Side Effects of Penile Injection

The most commonly reported side effect of intracavernosal alprostadil is pain at the injection site or in the penis itself. In head-to-head comparisons, about 47% of men using injection reported urogenital pain, compared to only 7% using the alternative urethral suppository delivery method.⁹ Pain tends to be brief and is often described as a burning or aching sensation that subsides within minutes, but it is a genuine barrier for some men.

A more serious concern with long-term use is penile fibrosis, the formation of scar tissue inside the penis. In one study of 245 patients on self-injection therapy, about 23% developed some degree of penile fibrosis. These men had been injecting an average of five times per month for roughly two and a half years, with an average dose of 13 micrograms per injection.¹⁰ Higher cumulative doses and more frequent injections increased the risk. Most guidelines recommend limiting injections to no more than three times a week and rotating the injection site on alternating sides of the penis to reduce this risk.

The most feared complication is priapism, a prolonged erection that won’t subside and can damage penile tissue if it lasts more than four hours. It is uncommon with alprostadil alone compared to older combination injectables, but it does happen, particularly when the dose is too high or the drug is combined with other agents. Case reports describe patients needing emergency surgical intervention when pharmacological reversal fails. One documented case involved a man who experienced ischemic priapism for three days following self-injection of a combination drug, ultimately requiring surgical shunting procedures to resolve.¹¹ This is one reason office-based dose titration is considered essential before home use begins.

Injection Versus Urethral Suppository

Because many men find the idea of a penile injection daunting, an alternative delivery method exists: the MUSE system (Medicated Urethral System for Erection), which involves placing a small alprostadil pellet into the urethra. The trade-off is convenience versus effectiveness. In a prospective randomized study, 90% of men receiving intracavernosal injection achieved a good erection during clinic dosing, compared to 60% using MUSE. At home over three months, intercourse was reported after 85% of injections versus 55% of MUSE applications.⁹

A separate comparative study of 103 men found an even wider gap: complete rigid erections occurred in 48% of men using injection compared to just 10% using MUSE. Ultrasound measurements confirmed that MUSE often failed to achieve full relaxation of the smooth muscle in the penile tissue.¹² Interestingly, the pain profile flips: MUSE caused penile burning in about 31% of users, while only about 11% of injection users in that same study reported pain. MUSE also introduced systemic side effects like dizziness, sweating, and low blood pressure in about 6% of patients, with occasional fainting episodes. Injection did not cause any of these systemic reactions.¹² Still, patients overwhelmingly found MUSE easier to use: 90% rated home treatment as easy with MUSE, versus 40% with injection.⁹

Why Many Men Stop Using It

Even though intracavernosal alprostadil works well, dropout rates are high. Understanding why matters, because the reasons are less about physical side effects than you might expect. One study found that the main reasons patients stayed in a self-injection program were satisfaction with results, a sense of improved self-esteem, and finding the injection process manageable. Those who dropped out were less motivated, less satisfied with the quality of their sexual experience on the medication, and perceived the effort of self-injection as substantial. Actual side effects and physical discomfort were not the primary drivers of quitting.¹³

Another study that tracked 144 men through the full arc of treatment painted a detailed picture. About 24% never started home therapy after their initial clinic visit, citing that the process felt unnatural (20%), dissatisfaction with results (20%), or improvement in spontaneous erections that made the treatment unnecessary (15%). Of those who did start home injections, 40% eventually dropped out, typically after about seven months. Their reasons included dissatisfaction (22%), cost (20%), and insufficient erection quality (19%).¹⁴ Among post-prostatectomy patients offered injection-based erectile rehabilitation, more than a third refused to start the program at all, with lack of sexual interest being the most common reason (about 52%), followed by the partner’s lack of interest (30%). Among those who started, about 19% dropped out within six months, mainly citing disappointment with how well it worked and injection-related pain or anxiety.¹⁵

Keeping the Ductus Arteriosus Open in Newborns

The other major use of PGE1 is in a completely different patient population. Some babies are born with heart defects where blood flow to the lungs or the body depends on a temporary blood vessel called the ductus arteriosus, which normally closes shortly after birth. Intravenous PGE1 keeps this vessel open, buying time until corrective heart surgery can happen. A recent study found that alprostadil was effective for this purpose in 88% of patients, with no meaningful difference between very-low-dose and low-dose regimens.¹⁶

The side effect profile in neonates is quite different from the adult urological context. The most concerning short-term risk is apnea, where the baby temporarily stops breathing. In a randomized trial testing whether caffeine could prevent this, apnea occurred in 42% of infants receiving PGE1 alone and 20% in those also given caffeine, although the difference did not reach statistical significance in that trial.¹⁷ Because of this apnea risk, neonates on PGE1 infusions are typically monitored in intensive care units with ventilatory support available.

When infusions continue for weeks or months, as sometimes happens in babies waiting for a heart transplant, a different complication emerges: cortical hyperostosis, an abnormal thickening of the outer layer of bones. A study of 86 infants on prolonged PGE1 found radiologic evidence of this bone thickening in 62%. The rate climbed steeply with longer treatment: 42% of infants treated for less than 30 days showed it, compared to 87% at 30 to 60 days, and 100% of those treated beyond 60 days.¹⁸ The severity of the changes tracked directly with total PGE1 dose and duration. This condition can mimic a bone infection on imaging, which makes diagnosis tricky.¹⁹ The bone changes are generally reversible once the infusion stops, but they underscore why neonatal teams weigh the risks of prolonged PGE1 carefully.

Peripheral Artery Disease

Intravenous PGE1 has also been used for severe peripheral artery disease, particularly in patients with critical limb ischemia who have run out of surgical or endovascular options. In one series of patients with severe lower-limb ischemia, intravenous alprostadil improved ulcers or tissue damage in 58% of cases, reduced pain in 86%, and helped save the limb in about 72%.²⁰

The evidence here is less clear-cut than for erectile dysfunction, however. A placebo-controlled randomized multicenter trial called ESPECIAL found that alprostadil did not show superiority over placebo for either complete healing of ulcers at 12 weeks or rates of major amputation at 24 weeks when looking at the overall study population.²¹ This discrepancy between the observational data showing benefit and the randomized trial showing no clear advantage is the kind of gap that haunts peripheral vascular research. It suggests the drug may help select patients in real-world scenarios while failing to demonstrate a broad enough effect to clear the high bar of a controlled trial. Use in this setting varies considerably by country and institution.

Combination Injectables and Diagnostic Applications

Alprostadil is sometimes used in combination with other drugs for penile injection, most commonly in two- or three-drug mixtures that include papaverine and phentolamine (often called “bi-mix” or “tri-mix”). These combinations can be effective when alprostadil alone does not produce an adequate response. However, approval of intracavernosal agents remains largely limited to alprostadil as a single agent, with aviptadil/phentolamine gaining approval in only a few regions. The lack of standardized combination formulations is a barrier to wider adoption.²²

Outside of treatment, alprostadil injection serves a diagnostic role. When urologists need to evaluate penile blood flow using Doppler ultrasound, they inject alprostadil to induce an erection so that blood vessel measurements can be taken under conditions that mimic sexual arousal. A study evaluating this procedure in 292 patients found a mean erection response of about 80% when using an average dose of roughly 9 micrograms.¹¹ Some patients do not achieve a full erection from the injection alone, which can lead to inaccurate readings on the ultrasound. Research has found that adding an oral dose of sildenafil to the standard alprostadil injection significantly improved blood-flow measurements and diagnostic accuracy, reducing the rate of false-positive findings of vascular disease.²³

Storage and Practical Handling

For patients who self-inject at home, how the drug is stored matters more than most people realize. PGE1 degrades when exposed to heat and light. Commercial formulations of alprostadil typically need refrigeration. Stability testing of alprostadil diluted in saline and stored in standard IV bags under refrigeration with light protection found the drug remained within acceptable potency through 10 days, but one sample exceeded the acceptable range by day 14.²⁴ This is particularly relevant for patients using compounded preparations rather than branded products, since compounded mixtures may lack the preservatives or stabilizers found in commercial formulations. Patients should keep the drug refrigerated, avoid leaving it in a warm car or bathroom, and pay attention to expiration dates and any changes in the solution’s appearance.

For the neonatal intravenous formulation, hospitals follow strict protocols for dilution and infusion rates, and the drug is prepared fresh for each use. The rapid degradation that makes PGE1 safe from a systemic standpoint also makes it finicky to store. In clinical settings where the drug is being infused continuously, tubing and solution bags are typically replaced on a regular schedule to ensure consistent delivery.

Erectile Rehabilitation After Prostate Surgery

One area where intracavernosal alprostadil occupies a specific niche is in the rehabilitation of erectile function after radical prostatectomy for prostate cancer. Even when a surgeon spares the nerves responsible for erection, recovery can take a year or more. During that window, many urologists prescribe regular low-dose penile injections or oral medications to promote blood flow and prevent the structural changes in penile tissue that can occur when erections stop for extended periods.

The reality of this process is often more discouraging than patients anticipate. In one study, when oral medications failed to restore erections at the one-year mark after surgery, patients were encouraged to continue rehabilitation with intracavernosal injections for at least another year.²⁵ Long-term tracking of return of spontaneous erections in men using alprostadil injection showed that an effective dose remained stable for most patients, with 94% continuing to respond and no need to escalate the dose over time.²⁶ The expectation that the injections are a bridge back to unassisted function is sometimes met, but for many men the injections become a longer-term solution than originally anticipated. The dropout data discussed earlier reflect this: when the psychological burden of injecting feels heavy and the promised return to normalcy keeps receding, motivation erodes. Realistic goal-setting at the start of the rehabilitation process tends to predict who sticks with it and who does not.