Pharmacokinetic considerations plasma half-life

Pharmacokinetics Tolcapone, taken orally, is readily absorbed, and its absorption is not influenced by food. It is extensively bound to plasma albumin (>99 percent), and has a small volume of distribution (0.13 L/kg). The plasma half-life is approximately two hours, although inhibition of COMT may last considerably longer due to its affinity for the enzyme. Tolcapone is extensively metabolized, and its metabolites are eliminated in both the urine and feces. Dosage may need to be adjusted in individuals with moderate or severe cirrhosis. 

Pharmacokinetic properties Naltrexone (Misra, 1981) is absorbed from the gastrointestinal tract, but is subject to considerable first-pass metabolism in the liver, yielding the active metabolite 6-beta-naltrexole. Naltrexone has low plasma binding of about 20%. The half-life of naltrexone is -3 h and of 6-beta-naltrexole is -13 h. 

Conversely, in another experiment using oral doses of 20, 50, 100 and 200 mg/kg to Balb C mice, broadly linear pharmacokinetics were observed. The maximum platinum levels in plasma were observed between 30 and 120 min and were delayed with increasing dose. Platinum unbound to proteins was detectable up to 7 hpost dosing. Elimination of total platinum was biphasic with a terminal half-life of 30 h. The half-life for ultrafilterable free platinum ranged from 87 to 135 min which is considerably longer than the 10 min reported for cisplatin or 25 min reported for carboplatin [25],... 

Mathematical models allow for considerable data compression. Data that fill many notebooks and/or tables may be summarized by means of the few parameters of a well chosen model. Plasma concentration versus time data collected during a pharmacokinetic study in many patients may be summarized using a volume of distribution term and an elimination half-life. Other models may include more parameters, but there is always a considerable compression in the information required to describe the overall results of the study. An extensive drug stability study involving many samples stored at various elevated temperatures may be summarized as a single time for 10% decomposition at room temperature. Determination of appropriate models can be a very useful method of summarizing an experimental study. 

Oxaprozin (Daypro) has similar pharmacological properties, adverse effects, and therapeutic uses to those of other propionic acid derivatives. However, its pharmacokinetic properties differ considerably. Peak plasma levels are not achieved until 3 to 6 hours after an oral dose, whereas its half-life of 40 to 60 hours allows for once-daily adminisffation. 

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