Continuing Education Activity

Alprostadil is a synthetic prostaglandin E1 analog primarily used as a second-line treatment for erectile dysfunction in males when oral therapy has failed. This drug is also utilized in specific cases to temporarily maintain the patency of the ductus arteriosus in newborns with congenital heart defects until surgical intervention. For erectile dysfunction, alprostadil is administered via intracavernosal injection or intraurethral suppository, with combination therapies such as "Trimix" offering enhanced efficacy. In neonates, alprostadil’s vasodilatory properties help maintain ductal patency in conditions such as transposition of the great arteries or coarctation of the aorta. The use of this drug requires careful hemodynamic monitoring due to risks of instability. Common adverse effects include hypotension, flushing, and priapism, which require immediate intervention if prolonged. 

This activity reviews the indications, mechanism of action, administration, contraindications, and adverse event profile of alprostadil in the treatment of erectile dysfunction in males and the presurgical management of ductus arteriosus–dependent congenital heart defects in newborns. This activity also underscores the importance of interprofessional collaboration, including effective communication and coordination among healthcare team members, and the use of combination therapies to optimize patient outcomes and manage potential risks associated with alprostadil.

Objectives:

• Identify the appropriate indications for alprostadil use, including its role in erectile dysfunction and ductus arteriosus management in neonates.
• Implement appropriate monitoring strategies for hemodynamic stability and adverse effects, such as hypotension and priapism, during alprostadil therapy.
• Select appropriate adjunct therapies, such as combination drugs, to optimize outcomes in patients using alprostadil for erectile dysfunction.
• Collaborate with an interprofessional healthcare team to ensure coordinated care and prompt intervention, optimizing patient outcomes in managing alprostadil's adverse effects.

Indications

Over 150 million people worldwide are affected by erectile dysfunction. Alprostadil is approved by the US Food and Drug Administration (FDA) as a second-line treatment for this condition and is typically used when first-line oral therapies, such as phosphodiesterase type-5 (PDE5) inhibitors (eg, sildenafil), prove ineffective.[1][2][3] Alprostadil can also be combined with other medications,[2] such as in the formulation known as "Trimix," which includes the combination of papaverine, phentolamine, and alprostadil. This medication is particularly effective when administered via intracavernous injection as a treatment for erectile dysfunction.[2][4][5] However, Trimix is only available through authorized compounding pharmacies, as it is not commercially manufactured.[6] Please see StatPearls' companion resource, "Erectile Dysfunction," for more information.

Alprostadil can also be a therapeutic option for the temporary maintenance of ductus arteriosus patency and other congenital heart conditions where ductal patency is critical for survival until surgical correction.[7][8] These conditions include both cyanotic defects (such as transposition of the great arteries [TGA], tetralogy of Fallot [TOF], tricuspid atresia, and pulmonary stenosis) and acyanotic defects (such as coarctation of the aorta and interruption of the aortic arch).[7][9][10] Alprostadil (administered by the intravenous [IV] route) is FDA-approved for temporarily maintaining ductus arteriosus patency in neonates with ductal-dependent congenital heart disease until surgical intervention.[7][8] Alprostadil induces vasodilation through a direct effect on vascular and ductus arteriosus smooth muscle.

In infants with restricted systemic blood flow, alprostadil can increase systemic blood pressure and reduce the pulmonary artery pressure-to-aortic pressure ratio. Diabetic peripheral neuropathy, the most common chronic complication of diabetes, can be effectively managed with lipo-prostaglandin E1 (PGE1), which improves neural function in affected patients.[11]

Topical alprostadil has shown promising results in the treatment of female sexual arousal disorder when used in clinical settings. However, further studies are needed to better define its role in managing this condition.[12]

Alprostadil is commonly used to manage ischemic changes in patients with Raynaud phenomena.[13] Additionally, PGE1 analogs have demonstrated efficacy as a conservative treatment option for lumbar spinal canal stenosis and as an adjunct therapy for foot necrosis caused by thromboangiitis obliterans.[14][15]

Contrast-induced nephropathy is among the top 5 leading causes of hospital-acquired acute renal injury. Alprostadil, combined with hydration therapy, has been shown to lower precontrast serum creatinine and blood urea nitrogen (BUN) levels, reducing the incidence of contrast-induced nephropathy.[16][17][18][19][20][21]

Alprostadil can inhibit platelet aggregation, stabilize cell membranes, and exhibit antioxidant properties.[22][23][24] Evidence suggests that alprostadil helps protect and improve kidney function by increasing renal blood flow, reducing cellular apoptosis, decreasing renal inflammation, and modulating the kidney's immunological response.[22][25][26][27] In addition, the drug has also been shown to reduce proteinuria and albuminuria.[27] 

These effects, collectively, of alprostadil may offer renal protection, especially for diabetic patients and other patients at risk of progressive kidney failure, in addition to its established use in treating contrast-induced nephropathy. Further research is needed to confirm this potential and assess alprostadil's role, if any, in patients at high risk of developing progressive renal failure.[22] Additionally, alprostadil is already used post-liver transplant to improve hepatic vascular flow and reduce ischemia-reperfusion injury.[28]

Mechanism of Action

Alprostadil is a synthetic analog of PGE1 with various pharmacologic effects. This drug binds as an agonist to prostaglandin receptors (eg, EP2), thereby activating adenylate cyclase. This results in an accumulation of 3'5'-cyclic adenosine monophosphate (cAMP), which is responsible for the pharmacological effects of the medication, including smooth muscle relaxation that leads to vasodilation (increasing peripheral and intracavernosal blood flow), bronchodilation, and inhibition of platelet aggregation.[29]

Administration

Intravenous Alprostadil

IV alprostadil is used to maintain and expand the patent ductus arteriosus before surgical correction.[7] The typical concentration for infusion is 10 to 20 mcg/mL. The usual starting dose is a continuous IV infusion at 0.025 mcg/kg/min, which can be adjusted as needed.[30] This dosage may range from as low as 0.01 mcg/kg/min to as high as 0.05 mcg/kg/min.[7][8]

Neonates with congenital cardiac defects and with a body weight of less than 2 kilograms are at an increased risk for apnea, particularly within the first 60 minutes of starting alprostadil infusion.[31] These high-risk patients should be closely monitored, with emergency respiratory measures available.[31]

Intracavernosal Alprostadil

Intracavernosal alprostadil is effective in treating erectile dysfunction due to its smooth muscle relaxation and vasodilatory properties. By relaxing the smooth muscle tissue of the corpus cavernosum, alprostadil widens the cavernosal arteries, increasing blood flow and leading to an erection. Alprostadil is the only FDA-approved agent for intracavernosal injections in the treatment of erectile dysfunction.

After intracavernosal administration, alprostadil is metabolized locally or through the lungs following systemic absorption. Short-term trials indicate that intracavernosal alprostadil is as effective as, or superior to, other drugs administered via the same route, including papaverine, phentolamine, linsidomine, and topical nitroglycerin (glyceryl trinitrate), for the treatment of erectile dysfunction.

Intracavernosal alprostadil is generally well tolerated; however, 20% to 40% of patients report pain following its administration. For this reason, Trimix is often preferred, as it significantly reduces the required alprostadil dose without compromising efficacy. Additionally, Trimix may be more cost-effective than standalone alprostadil injections, as smaller quantities of medication are needed to achieve similar results. 

Intracavernosal Injection Technique

This procedure typically uses a 1-cc syringe (often an insulin syringe) with a 0.5-inch, 27- or 30-gauge needle. Notably, it is recommended that the first intracavernosal injection be administered by a healthcare professional. This approach ensures patient safety and provides an opportunity for direct education on the proper injection technique and potential adverse events. After the initial injection, patients may perform self-injections at home, provided they adhere strictly to the prescribed dosing schedule. Patients must be carefully instructed never to exceed the recommended dose without explicit approval from their physician. Potentially severe adverse effects of intracavernosal alprostadil include priapism (4%) and fibrosis (8%).[32] 

To perform the injection, clinicians begin by cleaning the injection site with an alcohol wipe. The site should be on either lateral side of the penile shaft, between the base and the midpoint. The penis is stretched by hand, either away from or toward the body, to provide stability. The needle is inserted perpendicularly to the injection site. Care is taken to avoid visible superficial veins, the urethra (ventrally), and the neurovascular complex (dorsally). Direct pressure is applied to the injection site after syringe removal until any bleeding stops. Subsequent injections are alternated between sides. 

Additional resources for learning about intracavernosal injection techniques are available online. For example, detailed guidance can be found on the Memorial Sloan Kettering website (www.mskcc.org/cancer-care/patient-education/penile-injection-therapy). Additionally, free instructional videos are accessible on YouTube, including:

• Memorial Sloan Kettering: www.youtube.com/watch?v=pSuYwVRcM6c
• Cleveland Clinic: www.youtube.com/watch?v=-KGLryQMdsk
• Mayo Clinic: www.youtube.com/watch?v=Jub5zTCtT90

These resources provide visual and step-by-step instructions for safe and effective injection practices.

Intracavernosal Alprostadil Dosage Protocol and Safety Precautions

The intracavernosal dosage schedule for alprostadil typically begins with an initial injection of 2.5 mcg. Based on the response, additional doses may be administered, as mentioned below.

• If the initial injection elicits a partial response, an additional dose of 2.5 to 5 mcg may be administered.
• If the initial dose does not produce a response, a follow-up injection of 5 to 7.5 mcg may be administered.

Patients can resume test injections at home after 24 hours, increasing the dosage by 5 to 10 mcg every 24 hours until a satisfactory result is achieved. The objective is to produce an erection rigid enough for vaginal penetration, lasting no longer than 60 to 90 minutes.

• A maximum dose of 60 mcg is recommended, but the lowest effective dose should always be used.
• If the maximum dosage fails to provide satisfactory results, or if patients experience post-injection pain, intracavernosal therapy with Trimix should be considered.
• Intracavernosal injections should not be administered more than 3 times per week.
• Patients should be advised to seek immediate medical attention if an erection lasts longer than 3 hours to prevent potential permanent penile corporal injury.

Patients with neurogenic erectile dysfunction may be particularly sensitive to intracavernosal therapy. As described above, the same methodology is used, but the initial starting dose is 1.25 mcg, followed by a second dose of 2.5 mcg if necessary. At-home test injections may be increased by 5 mcg every 24 hours until a satisfactory result is achieved or a maximum of 60 mcg is reached.

Trimix for Intracavernosal Injection Therapy

Trimix is a standardized, compounded combination medication used for intracavernosal injection therapy in the treatment of erectile dysfunction. This drug comprises alprostadil, papaverine, and phentolamine, and is generally considered more effective and reliable than alprostadil alone. The effective dose of intracavernosal Trimix is typically about half the volume of alprostadil when used alone. This reduces both the cost and post-injection pain associated with alprostadil, as less PGE1 is required to achieve an equivalent erectile response.

The standard formula for Trimix consists of papaverine (30 mg), phentolamine (1-2 mg), and alprostadil (20 mcg/mL). Initial dosing typically starts at 0.2 cc, and the dose is gradually titrated upward in increments of 0.2 cc every 24 to 48 hours. The usual maximum intracavernosal dose of Trimix is 1 cc. For cases that are resistant to treatment, Quadmix (which includes 0.2 mg of atropine) and double-strength Trimix solutions are available. Overall success rates for alprostadil-based cavernosal injection therapy are estimated at 80%. In addition, the following strategies may enhance its effectiveness:

• Adding topical agents, such as topical Eroxon, can improve efficacy.
• Combining intracavernosal injections with PDE5 inhibitors can be highly effective, though the response may be unpredictable, and there is an increased risk of priapism.[33] However, this approach may be considered for severe erectile dysfunction when all other treatments have failed, and a penile prosthesis implant is the only alternative.[2][34][35][36][37][38][39]

Please see StatPearls' companion resource, "Erectile Dysfunction," for more information.

Risk of Priapism

The risk of priapism is thought to increase when intracavernosal injections are used in combination with PDE5 inhibitors, as their combined effects tend to be synergistic. However, a recent study showed that the priapism risk associated with this combination therapy is minimal. The erectile dysfunction response is significantly enhanced compared to using either treatment modality alone.[40] This suggests that combined intracavernosal injections and PDE5 inhibitors may be a viable option for patients who do not respond to standard or alternative therapies before considering penile prosthesis implantation.

Topical Alprostadil Therapy

Topical alprostadil therapy is associated with a high rate of discontinuation, similar to intracavernosal and transurethral treatments, which some patients find inconvenient or invasive.[41][42] However, several studies, including 4 double-blind, placebo-controlled, phase II trials, demonstrate that alprostadil topical cream is effective and well-tolerated in patients with mild-to-severe erectile dysfunction, those undergoing treatment for cardiovascular diseases and diabetes mellitus, and in otherwise healthy patients with erectile dysfunction.[41][42][43][44][45][46][47] Thus, alprostadil topical cream may be a suitable first-choice alternative for erectile dysfunction patients who do not respond to, cannot tolerate, or decline oral PDE5 inhibitor therapy.[42]

Intraurethral Alprostadil (MUSE) Therapy

Intraurethral alprostadil (medicated urethral system for erection or "MUSE") can be used as a suppository to treat erectile dysfunction, but it has been shown to be less effective in inducing cavernous smooth muscle relaxation and achieving erections compared to intracavernosal injections. Additionally, it is associated with more adverse effects, such as penile pain or burning, hypotension, and urethral bleeding. For these reasons, self-injection therapy with alprostadil remains the gold standard for managing erectile dysfunction when oral PDE5 inhibitors are ineffective or unsuitable. Intraurethral suppositories are typically considered for patients with refractory erectile dysfunction who are either unable or unwilling to use intracavernosal injection therapy.[48]

The medication is provided as a small, gel-like pellet, approximately the size of a grain of rice, inside a small plastic inserter. After urination, the stem of the applicator syringe is gently inserted into the urethra, and the plunger is pressed to release the pellet. Once the pellet is expressed, the syringe is removed, and the area of the penis where the pellet was inserted should be gently massaged to aid in liquefaction. As the medicated pellet dissolves, alprostadil is released into the urethra and absorbed into the corpora cavernosa.

Alprostadil pellets are available in 125 mcg, 250 mcg, 500 mcg, and 1000 mcg dosages, typically packaged in sets of 6. The cost can be high, especially if the initial dosage is inadequate or not well-tolerated. The recommended initial dose is usually 500 mcg. The primary adverse effect associated with intraurethral alprostadil therapy is burning at the site of pellet insertion.

Alprostadil Cream

Alprostadil cream is an effective treatment option for erectile dysfunction, especially when used in combination with vacuum devices and an elastic ring placed at the base of the penis to achieve sufficient rigidity for satisfactory vaginal penetration.[49] The cream can be applied topically to the glans or administered via intraurethral injection.[43][50][51] This treatment is safe, avoids the adverse effects associated with oral medications, requires no injections, and does not carry the risk of priapism. However, it is highly dependent on patient education and practice for optimal results, particularly when used with vacuum device therapy. Please see StatPearls' companion resource, "Erectile Dysfunction," for more information.

Intravenous Prostacyclin Analogs in Buerger Disease

IV prostacyclin (PGI2) analogs have been shown to be more effective than aspirin in managing rest pain and promoting healing of ischemic ulcers in Buerger disease.[52][53][54]

Adverse Effects

Adverse Effects of Intraurethral Alprostadil Suppositories (MUSE)

The use of intraurethral alprostadil suppositories (MUSE) may lead to the following adverse effects:

• Burning sensation in the urethra at the site of suppository deposition
• Central nervous system–related pain
• Dizziness
• Dysuria
• Headache
• Hypotension
• Leg discomfort
• Penile fibrosis
• Penile or urethral pain
• Perineal pain
• Priapism or prolonged erections
• Syncope
• Tachycardia
• Testicular pain
• Urethral bleeding (usually minor) 
• Urethral strictures 
• Vulvovaginal pruritus in female sexual partners [55][56]

Adverse Effects of Intracavernosal Alprostadil Use

The use of intracavernosal alprostadil may result in the following adverse effects:

• Balanitis
• Dizziness
• Headache
• Hypotension
• Injection site pain, bleeding, and bruising
• Injuries to the penis, including hematoma formation at the site of the injection
• Penile infections
• Penile pain (20% to 40% of patients)
• Peyronie disease
• Prolonged erection or priapism (less common)
• Rash on the penis
• Swelling of the penis

Adverse Effects of Intravenous Alprostadil Use

The use of IV alprostadil may result in the following adverse effects:

• Apnea
• Back pain
• Bronchoconstriction
• Cardiac disorders
• Cerebral hemorrhage
• Cough
• Diarrhea
• Disseminated intravascular coagulation
• Dizziness
• Edema
• Electrolyte imbalances (such as hypokalemia)
• Fever
• Flu-like symptoms
• Flushing
• Gastrointestinal upset
• Gastroesophageal reflux disease (GERD)
• Headache
• Hyperbilirubinemia
• Hypokalemia
• Hypotension
• Hypothermia
• Infection at the injection site or even sepsis
• Jitteriness
• Lethargy
• Nausea or vomiting
• Pain at the injection site
• Seizure
• Shock
• Stiffness
• Tachycardia or bradycardia
• Thrombocytopenia
• Upper respiratory infection

Contraindications

Alprostadil intraurethral suppositories (MUSE) should be avoided under the following conditions:

• Individuals with urethral strictures or Peyronie disease, as alprostadil use may cause further injury to the penis.
• Individuals with urethritis, as alprostadil may exacerbate the condition.
• Individuals with a known hypersensitivity to alprostadil or components of the dosage form.
• Individuals with Peyronie disease, as alprostadil can cause penile fibrosis and may exacerbate the condition.
• Individuals with sickle cell disease or trait, multiple myeloma, leukemia, polycythemia vera, or thrombocythemia, as these conditions can increase the risk of priapism.

Monitoring

When initiating alprostadil for erectile dysfunction, early identification of adverse effects is crucial for optimal outcomes. Alprostadil may cause hemodynamic instability, hypotension, and flushing. This drug is also recommended to monitor blood pressure, heart rate, and temperature both before and after the initial dose, as well as when increasing the dosage.

Alprostadil can cause penile pathologies, including stricture formation, fibrosis, and hematoma at the injection site. Regular physician examinations and prompt attention to any onset of discomfort can improve outcomes. Monitoring the duration of erection is crucial for understanding the drug's effects and tailoring management to the patient's needs. The lowest effective dose of alprostadil should be used, and patients should be advised not to increase the dose without specific instructions from their physician. They should also be reminded to seek emergency medical care if the erection lasts longer than 3 hours.

Toxicity

The use of alprostadil for the treatment of erectile dysfunction in males may lead to prolonged erections and, in some cases, priapism. The incidence of priapism as an adverse effect of alprostadil is more common with the intraurethral suppository. This condition can also occur when unauthorized combination therapy is used or when patients exceed the prescribed dosage.

Priapism is a genitourinary emergency that requires immediate evaluation and treatment. The assessment is primarily based on the physical examination and patient history, with penile ultrasonography and/or penile blood gas analysis used if the underlying cause is unclear.

Management of drug-induced priapism includes techniques such as aspiration of cavernosal blood, cold saline irrigation, and penile injections with diluted sympathomimetic agents.[57] In cases of intractable priapism, corporal dilation and penile prosthesis implantation can be effective, although they are invasive and rarely required if the condition is treated promptly.[58] Please see StatPearls' companion resource, "Priapism," for more information.

Enhancing Healthcare Team Outcomes

Managing erectile dysfunction with alprostadil, whether as an intracavernosal injection or intraurethral suppository, requires an interprofessional team of healthcare providers, including nurses, pharmacists, and physicians from various specialties. In addition to common causes like diabetes mellitus and hypertension, lifestyle factors such as obesity, lack of physical exercise, and lower urinary tract infections are also associated with erectile dysfunction and warrant attention. Without appropriate management and patient education, the morbidity related to the treatment itself can be significant.

Patient education is crucial for the proper use of alprostadil, whether as an intracavernosal injection or an intraurethral suppository, and is an essential aspect of management. Patients should be closely monitored for potential adverse effects of the drug, such as prolonged erections or priapism, penile fibrosis, urethritis, stricture formation, and circulatory disturbances leading to hypotension.

A psychiatrist should be consulted to evaluate for possible psychiatric issues that might contribute to erectile dysfunction. A sex therapist may be recommended for a more holistic management approach. A cardiology consultation is also advisable, as studies have shown an association between cardiovascular diseases and erectile dysfunction. Additionally, erectile dysfunction can serve as a strong indicator of coronary artery disease, warranting a cardiovascular assessment for noncardiac patients who present with unexplained erectile dysfunction.[59] Furthermore, the use of alprostadil can lead to circulatory issues, including significant hypotension.

Pharmacists should be prepared to counsel patients on the proper use of both intracavernosal and suppository formulations of alprostadil, as these treatments require patients to have strong administration technique skills. If pharmacists have concerns about the patient's ability to self-administer the medication or identify potential drug interactions during medication review, they should promptly contact the prescribing physician. Nurses can offer counseling, reinforce patient education, monitor adherence to dosing schedules, evaluate regimen effectiveness during follow-up visits, assess for adverse effects, and report any concerns to the prescribing physician.

Discussing reproductive and sexual health with men can be a sensitive and challenging task. It is important to approach these conversations with empathy and professionalism while building rapport with the patient. Sensitivity is key, as in some cultures, even the mention of a male sexual disorder can be particularly distressing. Adopting a positive and respectful approach, while emphasizing the high likelihood of a successful outcome, encourages a more open discussion of topics such as erectile dysfunction. A collaborative interprofessional team approach is essential to ensuring the most effective use of alprostadil therapy.

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Disclosure: Stephen Leslie declares no relevant financial relationships with ineligible companies.

Disclosure: Ashish Jain declares no relevant financial relationships with ineligible companies.

Disclosure: Omar Iqbal declares no relevant financial relationships with ineligible companies.