16 Pharmacological treatments

Pharmacokinetics The pharmacological treatment of the elderly differs from that of younger patients, mainly because of altered pharmacokinetics and the higher proportion of patients with organic disorders. Pharmacokinetics describes the way in which drugs reach their target tissues. Absorption Absorption is not grossly affected in the elderly although there are reductions in gastric pH, area of absorptive surface, mesenteric blood flow and transport enzymes (Lader, 1994). Distribution Changes in distribution in the elderly include: reduction in lean body mass and increase in body fat (fat acts as a reservoir for psychotropics, increasing their half-lives); reduction in body water (increased concentration of water soluble compounds, e.g. alcohol); reduction in plasma proteins such as albumin (increased levels of free drug); and reduction in cerebral blood flow. Metabolism This is reduced and is particularly important with polypharmacy. Liver blood flow decreases (by up to a third in over 65-year-olds (Bender, 1965)) and liver microsomes are less efficient (with some exceptions). Excretion Excretion is decreased. Glomerular filtration reduces by up to a half by the age of 70 (Papper, 1978). Plasma creatinine may be unreliable, so creatinine clearance is the preferred test of renal function.