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To the Editor: Some studies suggest that drug metabolism by Cytocrome P 3A4 450 (CYP3A4) differs by ethnic group. Nifedipine¹ and midazolam,² drugs considered to be markers of CYP3A4 activity, exhibit reduced clearance and higher bioavailability in Mexican men compared with white men. Sildenafil (Viagra, Pfizer Inc, New York, NY), a popular drug for the treatment of erectile dysfunction, is also biotransformed by CYP3A4.³ Therefore, we studied the pharmacokinetics of oral sildenafil in 24 healthy, young, male Mexican volunteers for 12 hours after a 100-mg dose.

Methods

Plasma concentrations of sildenafil and its main metabolite, desmethyl sildenafil, were determined by a high-performance liquid chromatographic method based on that described by Cooper et al.⁴ Plasma samples were extracted with benzene and analyses were performed using a reversed-phase C18 column eluted with a 0.02-mol/L 30% acetonitrile/70% NaH₂PO₄ buffer (flow rate, 1 mL/min) at room temperature. Spectrophotometric detection was carried out at 230 . . . [Full Text of this Article]

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