Effect of sildenafil citrate (viagra) on the ocular circulation

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Abstract

PURPOSE: Sildenafil citrate induces vasodilation by enhancing the smooth muscle relaxant effects of nitric oxide. We have previously reported that nitrate compounds, a different group of nitric oxide–mediated vasodilators used mainly for the treatment of ischemic cardiac diseases, produce an increase in optic nerve head circulation and retinal venous vasodilation. The purpose of the present investigation was to evaluate the effect of sildenafil on ocular circulation.

METHODS: In a double-blind, randomized, crossover trial, 15 healthy male volunteers received 100-mg doses of sildenafil citrate (Viagra; Pfizer, Inc, New York, New York) or matching placebo on 2 separate days. Laser Doppler flowmetry was used to assess foveolar choroidal and optic nerve rim circulatory parameters. Measurements were obtained in one eye at baseline, 1 hour, and 5 hours after dosing. Blood pressure and intraocular pressure were monitored, and perfusion pressure was calculated.

RESULTS: Mean optic nerve head blood flow measurements at baseline, 1 hour, and 5 hours were 11.6 ± 2.2 arbitrary units (± SD), 12.5 ± 2.8, and 12.1 ± 2.4 after sildenafil and 11.9 ± 2.5, 12.6 ± 3.1, and 13.0 ± 3.0 after placebo, respectively. When compared with placebo, no significant change in mean blood pressure, intraocular pressure, perfusion pressure, or choroidal or optic nerve circulatory parameters were observed after sildenafil treatment. The power to detect a 20% change in optic nerve head and choroidal blood flow after sildenafil was approximately 90%.

CONCLUSIONS: In comparison with placebo, no significant change in optic nerve rim or foveolar choroidal blood flow was observed after treatment with sildenafil. This suggests that nitrate compounds and sildenafil may differentially affect ocular circulation. Furthermore, no significant effects on intraocular pressure, systemic blood pressure, or ocular perfusion pressure were detected after sildenafil treatment.

Section snippets

Patients and methods

A randomized, placebo-controlled, crossover study of the effects of sildenafil citrate (Viagra; Pfizer, Inc, New York, New York) was performed in 15 healthy male volunteers with normal eyes. Volunteers aged 30 years or older (39 ± 8 years, average ± SD) with visual acuity of 20/25 or better were included in the investigation. All subjects had a normal intraocular pressure of 21 mm Hg or less and a normal eye examination. None of the subjects was receiving nitrate therapy. Subjects provided

Results

Experiments were designed to determine the effects of sildenafil on ocular blood flow. In comparison with placebo, no significant change in mean foveolar choroidal blood flow (ANOVA, P = .88) was observed after sildenafil treatment. Mean foveolar choroidal blood flow at baseline, 1 hour, and 5 hours, was 14.3 ± 3.3 arbitrary units (± SD), 13.4 ± 3.1 arbitrary units, and 13.1 ± 2.7 arbitrary units after sildenafil treatment, and 14.1 ± 3.6 arbitrary units, 13.1 ± 3.6 arbitrary units, and 13.2 ±

Discussion

Nitrate compounds are a group of vasoactive drugs widely used for the treatment of cardiac ischemic diseases because of their vasodilatory ability.13 However, similar to the effect of sildenafil, nitrates work by means of nitric oxide–mediated dilation of arteries and veins.14 Because the mechanism of action of sildenafil and nitrates both use the nitric oxide–cyclic guanosine monophosphate pathway, patients taking nitrates should not receive sildenafil.15 The combination of both drugs can have

Acknowledgements

The authors thank Dr Maureen Maguire for her statistical consultation supported by National Institutes of Health Clinical Vision Research Development Award EY10964.

References (19)

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This investigation was supported by a grant from Pfizer, Inc, New York, New York.

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