Drug Excretion
Drug excretion refers to the removal of drugs and their metabolites from the body. This process primarily occurs through the kidneys (renal excretion), but other routes, such as biliary, pulmonary, and glandular excretion, also play a role.
Renal Excretion
The kidneys are the major route of drug excretion, eliminating drugs through glomerular filtration, tubular reabsorption, and tubular secretion.
- Glomerular Filtration:
- Drugs and metabolites are filtered from the blood into the renal tubules.
- Only unbound (free) drugs can pass through the glomerular membrane.
- Tubular Reabsorption:
- Some drugs can be passively reabsorbed back into the bloodstream.
- Lipophilic drugs are more likely to be reabsorbed, while hydrophilic drugs remain in the urine for elimination.
- Tubular Secretion:
- Active transport mechanisms in the renal tubules actively secrete drugs from the bloodstream into the urine.
- This process can be influenced by drug interactions (e.g., competition for transporters).
- Factors Influencing Renal Excretion:
- Urine pH:
- Alkaline urine favors the excretion of acidic drugs (e.g., aspirin).
- Acidic urine favors the excretion of basic drugs (e.g., amphetamines).
- Renal function: Impaired kidney function reduces drug elimination, increasing drug half-life and risk of toxicity.