VIAGRA

Viagra 50mg

Active Ingredient: Sildenafil

Dosage Strengths: 25mg, 50mg and 100mg

Dosage Forms: Blue, film-coated, rounded-diamond shaped tablets.

Manufacturer: Pfizer

Indications: Treatment of erectile dysfunction

Effect of food on drug: The absorption of the drug is delayed by food, particularly high fat meals.

Do not take with drug:

  • Organic Nitrates – Isosorbide dinitrate, Isosorbide mononitrate, Nitroglycerin (glyceryl trinitrate) and Amyl nitrite. They are used for chest pain (angina).

    • Reason – additive vasodilation which can cause dangerously low blood pressure (hypotension).

    • Alternative – None

  • Alpha Blockers – Alfuzosin, Doxazosin, Terazosin, Tamsulosin. They are used for hypertension and/or benign prostatic hyperplasia.

    • Reason – Pharmacodynamic synergism which increases the risk of dangerously low blood pressure (hypotension).

    • Alternative – Separate dose of sildenafil > 25mg from dose of alpha blocker by 4 hours.

Reduce dose when taken with:

  • Potent CYP3A4 Inhibitors – Clarithromycin, Erythromycin (Antibiotics), Ketoconazole, Itraconazole, Fluconazole (Antifungals), Grapefruit juice etc.

Adverse Effects:

  • Headache

Administration:

  • Can be taken 30 minutes to 4 hours before sexual activity. To be taken not more than once a day.

Pharmacology:

  • Mechanism of action – Inhibits PDE-V (Phosphodiesterase 5) which increases cGMP (cyclic guanosine monophosphate) to allow smooth muscle relaxation.

  • Bioavailability – 40%

  • Peak Plasma Time – 60 minutes

  • Metabolism –  Liver by CYP3A4

  • Half-life – 3 to 4 hours

  • Excretion – Feces


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