The pharmacokinetics and beta-adrenoceptor blocking effects of conventional and sustained-release metipranolol have been studied in 6 healthy male volunteers given a single oral dose of 40 mg. Plasma drug concentrations determined by TLC and a radioreceptor assay, and the inhibition of exercise-induced tachycardia, were monitored for 48 h. Relevant amounts of active metabolites other than deacetylmetipranolol were not found. Compared to conventionally formulated metipranolol, the controlled-release product had a prolonged mean residence time (10.7 vs 5.5 h), the peak drug concentration was halved and the time to peak drug concentrations was delayed. Relatively constant plasma concentrations (cideal = 6.5 ng/ml) and a clinically significant reduction of exercise-induced tachycardia were maintained throughout a 24 h dosing interval. An individual deacetylmetipranolol plasma concentration-effect relationship was evaluated using the Emax model. Mean parameters were Emax 26% and C50 2.9 ng/ml.
Pharmacokinetics of a novel nootropic agent, alaptide, have been examined in plasma and brain of mice, rats and rabbits following an intravenous dose (1 mg kg-1). First-order equilibration rate constants between plasma and brain (kBO) were calculated by a two-compartment model with a linked compartment (brain). Brain alaptide equilibrates rapidly with the central compartment in mice and rats due to the high kBO/beta ratio. In rabbits the equilibration is much slower (kBO/beta approximately 1). Partition coefficients between brain and plasma calculated from areas under the brain and plasma concentration-time curves, are 0.479, 0.549 and 0.864, in mice, rats and rabbits, respectively.
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