Pharmacokinetics biological half life

A typical semi-log plasma concentration versus time plot is shown in Fig. 4. This figure shows that pharmacokinetic data can also be expressed in terms of a half-life, called the biological half-life, which bears the same relationship to kei as that shown in Eqs. (14) and (15). 

From 10 to 20% of an oral dose of miconazole is excreted in the urine, mainly as metabolites, within 6 days. About 50% of an oral dose may be excreted mainly unchanged in the feces. The elimination pharmacokinetics of miconazole have been described as triphasic, with a biological half-life of about 24 h. With an initial half-life of about 0.4 h, and intermediate half-life of about 2.5 h and elimination half-life of 24 h. Very little miconazole is removed by haemodialysis [3]. 

Mirex was rapidly cleared from the blood of rats following an intravenous injection of 10 mg/kg (Byrd et al. 1982). Mirex blood levels at 8 hours were less than 4% of the levels seen 2 minutes after injection. Pharmacokinetic modeling predicted that intravenously administered mirex was quickly cleared from the blood into a rapidly equilibrating compartment. Over the next several weeks, mirex was redistributed to a slowly equilibrating compartment, which acted as a depot for mirex storage (Byrd et al. 1982). The biological half-life of mirex was estimated to be 435 days (Byrd et al. 1982). 

Pharmacokinetics Pharmacokinetic studies found that the mean biologic half-life of Kogenate (rAHF) was about 13 hours. The mean biologic half-hfe of plasma-derived AHF in the same individuals was 13.9 hours. In a comparative pharmacokinetic study, Kogenate FS was shown to be similar to its predecessor product Kogenate. 

FIGURE 4-4 Influence of biologic half-life relationship between exposure level (E, upper left) and biomarker level (BM). Daily exposure levels were created by Monte Carlo sampling from auto-correlated lognormal distribution. Observation time is 400 days. Biomarker levels were calculated for three half-lives—1 day (upper right), 1 month (lower left), and 1 year (lower right)—with one-compartment pharmacokinetic model. 

Pharmacokinetics The drugs are effective orally. Most thiazides take 1 to 3 weeks to produce a stable reduction in blood pressure, and they exhibit a prolonged biological half-life (40 hours). All thiazides are secreted by the organic acid secretory system of the kidney (see p. 224). 

Frequency of dosing in pracfice is often greater than predicted from half-life, as durafion of biological acfivify is offen shorter than pharmacokinetic terminal half-life... 

Drug instability as delivered from conventional formulation Solubility Biopharmaceutical Low absorption High membrane binding Biological instability Pharmacokinetic and pharmacodynamic Short half-life... 

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