Normal changes in the aging body (normal physiology of aging) affect pharmacodynamics.
- Changes that affect the patient’s response to the drug.
- What the drug does to the body.
Drug effects (pharmacodynamics) are greatest on two important systems:
Because of the normal age-related changes in the CV system, older people have “stiff pump/stiff pipes/decreased adrenergic response.” This means it is more difficult to increase cardiac output and orthostatic effects will be more dramatic. Any medication that has an effect on the pump, the pipes, or rate – digoxin, diuretics, beta-blockers – is likely going to produce a “weak and dizzy” patient.
Central Nervous System
In older people, there are fewer cells and neurotransmitters. This means the CNS is more sensitive to subtle changes in its pharmacologic environment. In the vulnerable brain any medication that has a psychotropic effect (sometimes surprising ones like ranitidine – an anti-histamine – or dimenhydrinate – an anti-cholinergic) will have a tendency to cause an acute confusional state (delirium).
Revisit the case of Mrs. Agonistou for an example of “what the drug does to the (older) body”.