Bioavailability and pharmacokinetics of ketanserin in elderly subjects

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Abstract
The bioavailability of ketanserin has been examined in a cross-over experiment in 21 elderly subjects (aged 59–72 years) by administration of tablets (40 mg), solution (40 mg) and injectable solution (10 mg). After two weeks of treatment with 40 mg ketanserin tablets further 18 blood samples for analysis were collected under steady-state conditions. Plasma levels were measured by HPLC. The absolute bioavailability of ketanserin tablets was 52.7%; their relative bioavailability compared to a solution containing an equal quantity of active compound was 85.5%. Therefore, the low absolute bioavailability of ketanserin cannot be attributed to the formulation. The active compound was rapidly liberated from the tablet, reaching a peak of 103.8 ng/ml after 0.97 h. Individual plasma level-time curves were fitted to an open three compartment model and a half-life of 17.7±7.26 h was calculated for the terminal elimination phase. An average terminal elimination half-life of 15.4±4.2 ng/ml was found after administration of the ketanserin solution. Multiple dosing with 40 mg tablets b.d.s. resulted in an AUC over one dosing interval at steady-state of 666±201 ng × h/ml. The AUC extrapolated to infinity was 1200±405 ng × h/ml for the last tablet. This is 1.8-times the AUC in one dosing interval, and 2.3-times the AUC of a single dose. Under steady-state conditions, the mean peak plasma level was 155.1 ng/ml (1.08 h after dosing) and the terminal half-life was 19.1±5.1 h. For the metabolite ketanserinol terminal half-lives of 21.4 h after a single tablet and 31.0 h after discontinuation of multiple dosing were calculated. Compared to the parent compound there was much more marked accumulation of ketanserinol. Despite moderate accumulation and prolongation of the terminal half-life of ketanserin under steady-state conditions, dosage adjustment is not required in elderly people. First-pass metabolism and bioavailability remained in the range found in previous studies of ketanserin in young subjects.
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