Generic Name

Viagra

Mechanism

• Selectively inhibits PDE5 → prevents degradation of cyclic guanosine monophosphate (cGMP) in corpus cavernosum smooth muscle.
• Enhances nitric‑oxide (NO)–mediated vasodilation → increased cGMP keeps phosphodiesterase‑5 activity low, allowing smooth‑muscle relaxation and sustained blood flow during sexual stimulation.
• Improved erectile quality without autonomic activity; effect occurs only with sexual arousal, hence no spontaneous erections.

Pharmacokinetics

• Absorption: Rapid oral absorption; peak plasma concentrations ~ 0.5 h after a 50 mg dose.
• Distribution: Widely distributed; protein binding ~ 95%.
• Metabolism: Primarily hepatic via CYP3A4/5 → active metabolite N‑desmethyl‑sildenafil (≈30 % exposure).
• Elimination: T½ ~ 3.5 h for parent drug; 12–15 h for metabolite. Excreted via biliary and renal routes.

Key points for prescribing:
• Adjust dose in hepatic or renal impairment; avoid in severe hepatic disease → reduced clearance.
• Drug interactions: strong CYP3A4 inhibitors (e.g., ketoconazole) ↑ serum levels; strong CYP3A4 inducers (e.g., rifampin) ↓ efficacy.

Indications

• Erectile dysfunction in adult men; effective for:
• Primary ED and secondary ED (post‑prostatectomy, diabetes, hypertension).
• Recommended starting dose: 50 mg taken on-demand before sexual activity.
• Dose range 25 mg–100 mg; escalation to 100 mg if inadequate response at 50 mg.

> *Insufficient data support safety for non‑classical indications (e.g., pulmonary hypertension), though subsets like pulmonary arterial hypertension have separate indications.*

Contraindications

• Contraindicated:
• Concomitant use of nitrates (e.g., nitroglycerin) → risk of severe hypotension.
• Severe systemic hypotension or known cardiac arrhythmia unresponsive to therapy.
• Warnings:
• Nocturnal hypotension in patients on antihypertensives.
• Rare adverse events: priapism >4 h; careful monitoring for sexual activity duration.
• Causality with ocular side‑effects (e.g., transient visual perturbations); patients with monocular vision should use caution.
• Caution in patients with pelvic trauma or spinal cord injury; consult urology.

Dosing

• On‑demand dosing:
• 50 mg orally with water ≤ 30 min before sexual activity.
• 100 mg if efficacy inadequate at 50 mg and other contraindications absent.
• Fixed‑dose daily regimen (if required): 25–50 mg daily for continuous effect, especially in patients with unpredictable sexual activity.
• Food interference: High‑fat meals delay absorption; take *sildenafil* on an empty stomach for optimal onset.

Monitoring

• Baseline: BP, HR, and renal/hepatic function (AST/ALT, creatinine).
• Periodic:
• Annual BP if antihypertensive therapy concurrent.
• Monitor liver enzymes 1–3 months after therapy initiation in high‑risk groups (e.g., chronic liver disease).
• Ophthalmologic assessment in patients with ocular pre‑existing conditions or prior vision changes.

Clinical Pearls

• Immediate post‑dose curve: *Viagra* peaks within 30–60 min—if fluids or fatty meals delay onset, consider lowering dose or rescheduling.
• Water‑or‑food intake: Avoid high‑fat meals 4–6 h before dosing to prevent delayed absorption, especially in patients with dyspepsia.
• Interaction nuance: Ketoconazole elevates *sildenafil* exposure by ~ 4–5×—consider dose reduction or avoid concurrent use.
• "No‑dose" strategy: For patients with high risk of priapism (testosterone replacement), instruct them to use 50 mg only if erection is satisfactory; avoid above 100 mg.
• Dose escalation algorithm: Start 50 mg → increase 25 mg increments up to 100 mg; monitor for side‑effects.
• Contraindicated device: Non‑surgical penile prosthesis with *sildenafil* may elevate bleeding risk from device manipulation; evaluate risk before prescribing.
• Administration timing: Morning dosing for daily therapy may coincide with circadian BP patterns; consider patient’s typical activities.
• Use in small populations: In patients ≥ 75 y, maintain careful monitoring for hypotension; dose reduction to 25 mg often safe.
• Idiopathic hypogonadism: Combine *sildenafil* with testosterone replacement only after verifying patient urogenital health—evaluate for potential interactions on responsiveness.

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• End of drug card – *Viagra* is a cornerstone PDE5 inhibitor for ED, yet requires careful attention to dose, drug interactions, and contraindications. Medical professionals should use this concise reference to inform patient counseling and clinical decision‑making.