[Pharmacotherapy in the aged].

The relatively high incidence of adverse drug reactions in the aged is a consequence of polypharmacy on the one hand and of altered pharmacokinetics on the other, changes of intrinsic or receptor properties (pharmacodynamic factors) are usually not of primary importance. Plasma half-lives increase and total clearance rates of many drugs are reduced due to diminished drug metabolism and renal excretion. With the exception of actively transported substances the amount absorbed from the gastrointestinal tract is not altered. Total body water declines with age, whereas the relative content of adipose tissue increases. Hence, the volume of distribution of hydrophilic drugs may be decreased, that of lipophilic drugs increased. The maintainance dose in old age can be calculated from the changes in plasma half-lives or, preferably, total clearance rates, the initial dose is determined by the changes in the volume of distribution. At present there is no rational basis for the use of geriatric drugs, i.e. agents claimed to retard the process of aging.