Why are the elderly more susceptible to osmolar disorders
Why are the elderly subjects more susceptible to osmolar disorders such as hyponatremia and hypernatremia?
With inability to maximally dilute urine, the elderly subjects face a greater likelihood for hyponatremia when situations lead to increased arginine vasopressin (AVP) secretion or response.
Medications such as morphine (high dose), nicotine, vincristine, and cyclophosphamide can enhance, whereas chlorpropamide, tolbutamide, nonsteroidal agents, and lamotrigine may promote AVP action. Age-associated decreased prostaglandin synthesis inhibits water diuresis and also predisposes the older individual to hyponatremia.
Hyponatremia with thiazide-type diuretics, commonly used to treat hypertension, is more common in the elderly. Similarly, the presence of a decreased thirst response in addition to a urinary-concentrating defect can predispose older individuals to dehydration and hypernatremia. Medications associated with decreased AVP secretion such as morphine (low dose), fluphenazine, promethazine, carbamazepine, and Haldol, or decreased AVP response including propoxyphene, demeclocycline, glyburide, and lithium, may increase likelihood of developing hypernatremia in older patients.