Pharmacokinetics is the study of the rates of absorption and elimination of drugs by

Chapter 22, Problem 22.31

(choose chapter or problem)

Pharmacokinetics is the study of the rates of absorption and elimination of drugs by organisms. In most cases, elimination is slower than absorption and is a more important determinant of availability of a drug for binding to its target. A drug can be eliminated by many mechanisms, such as metabolism in the liver, intestine, or kidney followed by excretion of breakdown products through urine or faeces. As an example of pharmacokinetic analysis, consider the elimination of beta adrenergic blocking agents (beta blockers), drugs used in the treatment of hypertension. After intravenous administration of a beta blocker, the blood plasma of a patient was analysed for remaining drug and the data are shown below, where c is the drug concentration measured at a time t after the injection. t/min 30 60 120 150 240 360 480 c/(ng cm3) 699 622 413 292 152 60 24 (a) Is removal of the drug a first- or second-order process? (b) Calculate the rate constant and half-life of the process. Comment. An essential aspect of drug development is the optimization of the half-life of elimination, which needs to be long enough to allow the drug to find and act on its target organ but not so long that harmful side-effects become important.