SildenafilRx

Trade Names: Viagra, Revatio

Drug Class: Phosphodiesterase 5 (PDE5) inhibitor

Preparations: Revatio 20 mg, Viagra 25-, 50-, 100 mg tablets

Dose: For pulmonary hypertension 20 mg three times daily; for erectile dysfunction 50 mg 1 hour before sex

Indications: Erectile dysfuntion (Viagra), pulmonary arterial hypertension (Revatio), sildenafil also tried in Raynaud’s and for digital ulcers associated with scleroderma

Mechanism of Action: Inhibits PDE5 and thus increases cyclic GMP concentrations causing vasodilation

Contraindications: Hypersensitivity, concurrent use of any form of  nitrates, including  ointment

Precautions: Potential for drug interactions; not recommended for children with pulmonary hypertension (increased mortality)

Pregnancy Risk: B

Adverse Effects
Common: Flushing, headache, dyspepsia, dizziness
Less common: Visual disturbance including color changes, allergy, rash, hearing loss, hypotension (particularly with nitrates or cytochrome P450 (CYP)3A  inhibitors), priapism

Drug Interactions
CYP3A inhibitors (strong inhibitors include clarithromycin,telithromycin, ketoconazole, itraconazole, nefazodone  and many HIV drugs; moderate inhibitors include aprepitant, diltiazem, verapamil, erythromycin, fluconazole, posaconazole, voriconazole, grapefruit juice): Increased  sildenafil concentrations.
Nitrates: Hypotension; avoid this combination
Alpha-1 blockers: Increased risk of hypotension

Patient Instructions: Avoid grapefruit juice; stop drug if have sudden visual or hearing loss

Comments: Small studies or case-series suggest PDE5 inhibitors are modestly effective for Raynaud’s and digital ulcers associated with scleroderma.

Clinical Pharmacology: Onset 60 minutes, duration 2-4 hours, half-life 4 h. Metabolized by CYP3A4.

BIBLIOGRAPHY

Roustit M, Blaise S, Allanore Y, et al.vPhosphodiesterase-5 inhibitors for the treatment of secondary Raynaud's phenomenon:systematic review and meta-analysis of randomised trials. Ann Rheum Dis 2013;72:1696-9. PMID: 23426043.

Tingey T, Shu J, Smuczek J, Pope J. Meta-analysis of healing and prevention of digital ulcers in systemic sclerosis. Arthritis Care Res 2013;65(9):1460-71. PMID: 23554239.