Responsiveness to Drugs at Extremes of Age
In general, responsiveness to drugs depends on a combination of pharmacokinetic and pharmacodynamic factors. The pharmacokinetic factors are those which govern the absorption of drugs, transport to their sites of action, distribution to various tissues, metabolism and elimination. The pharmacodynamic factors are those which govern the type, intensity and duration of action of drugs. Studies on drug responses at extremes of age must examine both sets of factors. Increased central effects of a drug could be due to either increased penetration into the central nervous system or to altered tissue response. Pharmacokinetic processes are of course easier to study particularly with the advent of increasingly sensitive and specific methods of measuring drugs and their metabolites in biological fluids. These studies are also easier in adult subjects since it is of course easier to obtain repeated adequate blood samples. As a result there is a relative abundance of pharmacokinetic studies in the elderly. However, even in infants and children increasingly complex pharmacokinetic studies can be attempted as more sophisticated methodology allows the use of small samples of blood.
KeywordsPlacebo Warfarin Propranolol Glucagon Diphenylhydantoin
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