Pharmacokinetics, disposition and biotransformation of [14C]-radiolabelled valsartan in healthy male volunteers after a single oral dose

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Abstract
1. The disposition of valsartan, a potent angiotensin II receptor antagonist, was investigated in six healthy male volunteers. They each received a single oral dose of80 mg of a C-labelled preparation as a neutral buffered solution. 2. Peak concentrations of radioactivity and valsartan in plasma measured 1 h after dosing showed rapid onset of absorption. The results of this study combined with other available data indicate that at least 51% of the dose was absorbed. 3. Valsartan was the predominant radioactive compound in plasma. Elimination of valsartan and radioactivity was fast and multiexponential. beta -Half-lives of 6 1 h were observed. In aterminal elimination phase, low radioactivity levels decreased with ahalf-life of81 33 h.Aminor, pharmacologically inactive metabolite (valeryl-4-hydroxy-valsartan; M1) was detected in the plasma at time points later than 2 h after dosing, representing approximately 11% of the AUCh of plasma radioactivity. 4. The bulk of the dose was excreted within 4 days. The totalexcretion within 7 days amounted to 99 1% of dose. Faecal excretion was predominant (86 5% of dose). Valsartan was largely excreted unchanged (81 5% of the dose in the excreta). The predominant clearance mechanism appeared to be direct elimination via bile. 5. An inactive metabolite, M1, was formed by oxidative biotransformation and accounted for 9 3% of the dose in the excreta.