To: DaiS who wrote (19167 ) 3/1/1999 11:48:00 PM From: Zebra 365 Read Replies (2) | Respond to
O T - My last word on splitting hairs, er, pills.Viagra is just a pill, active drug mixed with inert filler and coated with a film, it is homogenous enough that the small error from splitting should not be significant when compared with the other factors I have mentioned above. each tablet contains the following inactive ingredients: microcrystalline cellulose, anhydrous dibasic calcium phosphate, croscarmellose sodium, magnesium stearate, hydroxypropyl methylcellulose, titanium dioxide, lactose, triacetin, and FD & C Blue #2 aluminum lake. absolute bioavailability of about 40% . Its pharmacokinetics are dose-proportional over the recommended dose range. It is eliminated predominantly by hepatic metabolism (mainly cytochrome P450 3A4) and is converted to an active metabolite with properties similar to the parent, sildenafil. The concomitant use of potent cytochrome P450 3A4 inhibitors (e.g., erythromycin, ketoconazole, itraconazole) as well as the nonspecific CYP inhibitor, cimetidine, is associated with increased plasma levels of sildenafil (They never mention grapefruit juice here which is a more potent inhibitor than any of the above - Zebra) (see DOSAGE AND ADMINISTRATION). Both sildenafil and the metabolite have terminal half lives of about 4 hours. When VIAGRA is taken with a high fat meal, the rate of absorption is reduced, with a mean delay in Tmax of 60 minutes and a mean reduction in Cmax of 29%. The mean steady state volume of distribution (Vss) for sildenafil is 105 L, indicating distribution into the tissues. Sildenafil and its major circulating N-desmethyl metabolite are both approximately 96% bound to plasma proteins. Protein binding is independent of total drug concentrations.
