Overview
Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor used to treat erectile dysfunction. It enhances erectile function during sexual stimulation by increasing blood flow to the penis. The drug is not indicated for use in females and has significant interactions with nitrates and certain antihypertensives.
Mechanism of Action
Sildenafil selectively inhibits phosphodiesterase type 5 (PDE5), which degrades cyclic guanosine monophosphate (cGMP) in the corpus cavernosum. This inhibition increases cGMP levels, leading to smooth muscle relaxation and increased blood flow to the penis during sexual stimulation, facilitating erection.
Indications
- Treatment of erectile dysfunction
Common Doses
- 25 mg
- 50 mg
- 100 mg
Dosage
Typical starting dose is 50 mg taken approximately 1 hour before sexual activity, with a range of 25-100 mg based on efficacy and tolerability. Maximum recommended dosing frequency is once daily. Dose adjustment is recommended for patients >65 years, hepatic impairment, or severe renal impairment.
Contraindications
- Concomitant use with nitrates (organic nitrates or nitric oxide donors)
- Hypersensitivity to sildenafil or any component of the formulation
Side Effects
- Headache
- Flushing
- Dyspepsia
- Abnormal vision (blue-green color discrimination difficulties)
- Nasal congestion
- Back pain
- Myalgia
- Nausea
- Dizziness
- Rash
- Hypotension
- Priapism
- Sudden hearing loss
Interactions
- Nitrates (contraindicated due to severe hypotension)
- Alpha-blockers (increased risk of hypotension)
- Antihypertensives (additive blood pressure lowering)
- Ritonavir and other strong CYP3A4 inhibitors (increased sildenafil exposure)
- Alcohol (may increase hypotensive effects)
- Other PDE5 inhibitors (avoid concomitant use)
Counseling Points
- Take approximately 1 hour before sexual activity
- Do not take more than once daily
- Sexual stimulation is required for medication to work
- Seek immediate medical attention for erection lasting >4 hours
- Avoid concomitant use with nitrates
- Report sudden hearing loss or vision changes
- Discuss cardiovascular risk with healthcare provider
- Use protection against sexually transmitted diseases