Effects of aging

Effects of aging

Drug-receptor interaction

• Brain receptors become more sensitive, making psychoactive drugs very potent.

Metabolism

• Liver mass shrinks.
• Hepatic blood flow and enzyme activity decline.
• Metabolism drops to 1/2 to 2/3 the rate of young adults.
• Enzymes lose ability to process some drugs, thus prolonging drug half-life.

Absorption

• Gastric emptying rate and gastrointestinal motility slow.
• Absorption capacity of cells and active transport mechanism decline

Circulation

• Vascular nerve control is less stable.
• Anti-hypertensives, for example, may overshoot, dropping BP too low.
• Digoxin, for example, may slow the heart rate too much.

Excretion

• In kidneys, renal blood flow, glomerular filtration rate, renal tubular secretion and reabsorption, and number of functional nephrons decline.
• Age-related changes increase half-life for renally excreted drugs.
• Oral antidiabetic drugs, among others, stay in the body longer.

Distribution

• Lean body mass falls.
• Adipose stores increase.
• Total body water declines, raising the concentration of water-soluble drugs, such as digoxin, which can cause heart dysfunction.
• Plasma protein levels decrease, reducing sites available for protein-bound drugs and raising blood levels of free drug.