As one ages, blood pressure and hemodynamic changes become apparent. This is reflected in a fall in cardiac output and a gradual increase in total peripheral-vascular resistance. Systolic hypertension is one of the fundamental abnormalities of the cardiovascular system in the elderly. Baroreceptor function and cerebral blood flow likewise may be compromised and result in altered drug sensitivity. Renal function decreases with age and is manifested by a decrease in renal blood plasma flow and in glomerular filtration rate. There is a gradual blunting of sympathetic nervous system responsiveness demonstrated by a decrease in the activity of the renin-angiotensin-aldosterone system. Finally, pathways of drug biotransformation may be altered, resulting in adverse drug reactions.