For example, the antimalarial drug chloroquine has a high clearance but a very long half-life due to its large volume of distribution. The volume of distribution and clearance of a drug influence the half-life (eqn ). The half-life is useful to estimate the dosing interval, the duration of action of a drug, and the time required to attain steady-state plasma concentrations during a multiple dosage regimen. It takes five elimination half-lives for ∼97% of the bioavailable dose to be eliminated from the body.
The half-life is independent of the dose of the drug administered and is a useful indicator of how fast a drug is removed from the body. The elimination half-life ( t 1/2) is the time required for the amount of drug in the body to decrease by half (eqn ). Enantioselective bioanalytical methods are needed to study disposition and metabolism of individual enantiomers. In summary, carvedilol is a racemic drug, with S(−) and R(+) enantiomers differing significantly in their pharmacodynamic activities and PK properties. Only about 16% of carvedilol or its metabolites are excreted in the urine. Carvedilol is eliminated mainly by hepatic metabolism and most of the metabolites are excreted into the bile and eliminated via feces.
, revealed differences upon oral administration of 50 mg dose in the elimination half-lives between two enantiomers with values of 9.6 and 22.1 h for R(+) and S(−) enantiomers, respectively. A study on stereoselective disposition of carvedilol in man, conducted by Neugebauer et al. The elimination half-life for orally administered Carvedilol is typically 6–7 h, although different values are reported by various resources. Jasmina Novakovic, in Profiles of Drug Substances, Excipients and Related Methodology, 2013 5 Elimination
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