OCULAR SAFETY OF VIAGRA (SILDENAFIL CITRATE): INTRODUCTION

Viagra (sildenafil citrate) is the first of a new class of orally effective treatments for erectile dysfunction. It potently inhibits cGMP-specific phosphodiesterase type 5 (PDE5) (Fig 1),

found in high concentrations in the smooth-muscle cells of corpus cavernosum and in lesser concentrations in blood vessels of the systemic circulation. Because of its ability to act as a mild vasodilator, sildenafil was originally investigated as an antianginal agent, but that course of investigation was abandoned. Sildenafil also weakly inhibits PDE6 (Table I). PDE6 is present in high concentrations in cone and rod cells . Sildenafil (Viagra) has a plasma half-life of about 4 hours and a time to peak plasma concentration of 1 hour. Abnormal vision,

described as a blue tinge to vision or an increased brightness of lights, has been reported by 3% of patients treated with sildenafil in flexible-dose studies. In trials where subjects received fixed doses of sildenafil (5 to 200 mg) from the beginning of the study, the reports of abnormal vision were

found to be dose-dependent (Fig 2). The effects of sildenafil on vision are likely due to inhibition of the retinal PDE6 isozyme.

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