DRUG-INDUCED POSTURAL HYPOTENSION

Therapeutic drugs are the main cause of postural hypotension, notably in elderly people. This syndrome is harmful as it reduces patients' compliance with treatment and is responsible for severe accidents. Drugs which lower cardiac output by acting on heart rate and cardiac muscle contractility, and drugs which decrease blood volume may produce postural hypotension ; diuretics are often responsible for hypovolemia and hypokalaemia. The principal mechanisms involved are interferences of drugs with vegetative blood pressure regulation. They include vasomotor centre depressors (morphin-like compounds, antihypertensive 'agents, neurosedatives, neuroleptics, antiparkinsonians) ; ganglioplegics ; inhibitors of noradrenaline production (methyldopa, disulfiram) or re-uptake (antidepressants) ; catecholamine depressors (guanethidine) ; drugs acting on chromaffin granules (monoamine oxidase inhibitors) and those which inhibit post-synaptic receptors (alpha- and beta-blockers). Drugs which act on vascular smooth muscle tone (nitrites, calcium channel antagonists, angiotensin-converting enzyme inhibitors) occasionally cause postural hypotension. To the actions of these drugs must be added endogenous and exogenous factors and notably physiological ageing of the baroceptor reflex ; these factors must be taken into account whenever therapeutic drugs are prescribed.