Sildenafil (Viagra) For Erectile Dysfunction

Sildenafil, marketed as Viagra among other names, is a well-known medication for treating erectile dysfunction and pulmonary arterial hypertension. It’s sometimes used off-label to address symptoms of secondary Raynaud’s phenomenon. However, its effectiveness for female sexual dysfunction remains unclear. 

Sydenafil  can be administered orally (swallowed), intravenously (injected into a vein), or sublingually (dissolved under the tongue). Sildenafil inhibits the enzyme phosphodiesterase type 5 (PDE5), which breaks down cyclic guanosine monophosphate (cGMP). By blocking PDE5, sildenafil helps to maintain higher levels of cGMP in both the penile and pulmonary tissues. This increase in cGMP leads to smooth muscle relaxation and vasodilation. For the penis, this results in increased blood flow into the erectile tissues, allowing for a firmer and longer-lasting erection. In the pulmonary vasculature, it helps alleviate symptoms of pulmonary arterial hypertension by improving blood flow. When taken orally, sildenafil usually starts working within twenty minutes, and its effects can last up to two hours. Common side effects include:

• Headaches
• Heartburn
• Flushed skin
• Difficulty falling asleep
• Tingling or numbness in the arms, feet, legs, or hands
• Difficulty differentiating between colours like blue and green

Individuals with cardiovascular issues need to use sildenafil with caution. Rare but severe side effects include vision changes, hearing loss, and prolonged erections (priapism), which can potentially cause damage to the penis. Sildenafil should not be combined with nitric oxide donors, such as nitroglycerin, as this can cause a dangerous drop in blood pressure.

Tadalafil (Cialis) For Erectile Dysfunction

Tadalafil, marketed as Cialis among other names, is a medication used to manage erectile dysfunction, benign prostatic hyperplasia, and pulmonary arterial hypertension. It was approved in the U.S. in 2003 and is available as a generic drug. In 2021, it was the 171st most commonly prescribed medication in the U.S., with over 3 million prescriptions. It is taken orally, with effects typically beginning within half an hour and lasting up to 36 hours.

Common side effects include:

• Headache
• Muscle pain
• Flushed Skin
• Nausea. 

Rare but severe side effects can include prolonged erections (priapism) that might damage the penis, as well as vision and hearing problems. Tadalafil should not be combined with nitrovasodilators, like nitroglycerin, as it can cause a dangerous drop in blood pressure.

Tadalafil works similarly to Viagra due to being a PDE5 inhibitor due to tadalafil increasing blood flow to the penis, facilitating erections, and also dilates blood vessels in the lungs, reducing pulmonary artery pressure. However, Cialis remains effective for up to 36 hours, compared to Viagra’s 4–6-hour duration. Both medications should be taken approximately 30 minutes before sexual activity. Cialis may lead to limb pain, whereas Viagra can cause vision changes, rash, and dizziness.

Alprostadil For Erectile Dysfunction

Alprostadil is a prescription medication used to treat erectile dysfunction. It works by dilating blood vessels, which increases blood flow to the penis, thereby facilitating an erection. Alprostadil can be administered either via direct injection into the penis or as a suppository inserted into the urethral opening at the tip of the penis. The injectable form is marketed under the brand names Caverject, Edex, and Prostin VR. At the same time, the suppository is known as MUSE (Medicated Urethral System for Erection). 

Alprostadil is intended solely for use in men with erectile dysfunction and, if not used correctly, can cause permanent damage to the penis. The injectable version achieves a satisfactory erection in over 80% of men with erectile dysfunction, regardless of age or the underlying cause. However, the suppository is less effective, producing an erection in about 30% to 40% of men with erectile dysfunction.

Alprostadil has a different mechanism of action when compared to Viagra or Cialis. Alprostadil, a synthetic analog of prostaglandin E1 (PGE1), exerts its effects through several pharmacologic actions. It acts as an agonist at prostaglandin receptors, such as EP2. This activation stimulates adenylate cyclase, leading to increased cyclic adenosine monophosphate (cAMP) levels. The rise in cAMP results in smooth muscle relaxation and vasodilation, which enhances peripheral blood flow and helps facilitate erections. Additionally, alprostadil promotes bronchodilation and inhibits platelet aggregation.

When used as an intraurethral suppository (Medicated Urethral System for Erection, MUSE), alprostadil can cause:

• Urethral strictures
• Hypotension
• Syncope
• Penile/urethral pain
• Priapism (prolonged erection)
• Penile fibrosis
• Headache
• Dizziness

For intracavernosal use, side effects include:

• Hypotension or hypertension
• Dizziness
• Headache
• Less common priapism
• Rash on the penis
• Swelling of the penis
• Penile infections
• Injuries to the penis, including hematoma at the injection site

When used intravenously, alprostadil may cause:

• Flushing
• Hypotension or hypertension
• Tachycardia or bradycardia
• Dizziness
• Headache
• Electrolyte imbalances (e.g., hypokalemia)
• Nausea and vomiting
• Gastrointestinal upset
• Infection at the injection site or sepsis
• Pain at the injection site
• Cough
• Flu-like symptoms
• Gastroesophageal reflux disease (GERD)
• Bronchoconstriction