Pharmacodynamics describes the course of action of a drugs and aging at the effector organ level, in terms of duration and magnitude of action, and amplitude of and time to reach the peak action, for both therapeutic and adverse actions. Alterations in the number and affinity of drug receptors, postreceptor signaling processes, biochemical responses, homeostatic mechanisms, and body composition, in addition to higher likelihood of polypharmacy and concurrent pathological processes in older age, make elders more susceptible to adverse drug reactions, drug–drug interactions, or decreased/ increased sensitivity to some drug action. Among the drugs reported to have increased sensitivity in older age are benzodiazepines, dopaminergic agents, H1antihistamines, metoclopramide, neuroleptics, opioids, and warfarin. The drugs found to have decreased sensitivity in older age include ß-agonists, ß-blockers, furosemide, and vaccines.
Nonetheless, inconsistent definitions and screening approaches for adverse drug reactions, and methodology for data collection, sampling, and evaluation, yield controversial reports with regard to elders’ higher vulnerability to adverse drug reactions. Proper knowledge about the pharmacodynamics of a drug, in addition to its pharmacokinetic age-related characteristics, should establish the foundation for medication choice and dose adjustment in geriatric patients.
Old age is characterized by deterioration of the function of many regulatory processes, the functional integration between the cells and organs. Therefore, it may be a lack of maintenance of homeostasis under conditions of physiological stress. The decline reduced the ability of the homeostasis of the different arrangements in different areas, which explains at least part of the variability of the cycles increases occur in the elderly. Major pharmacokinetic and pharmacodynamic changes occur with increasing age. Pharmacokinetic changes include a reduction in renal and hepatic clearance and increased volume of distribution for fat-soluble drugs (hence the extension of the half-life) include the pharmacodynamic changes altered (usually) increased sensitivity to several classes of drugs such as anticoagulants, cardiovascular drugs and psychotropic substances. This review focuses on the main physiological changes associated with aging, the effects on different organ systems and their effects on the pharmacokinetics and pharmacodynamics of drugs.
