Which renal clearance processes are the main routes of urinary drug elimination?

Which renal clearance processes are the main routes of urinary drug elimination?

• A. Glomerular filtration, passive diffusion, and tubular reabsorption.
• B. Tubular reabsorption only.
• C. Glomerular filtration and active tubular secretion only.
• D. Glomerular filtration, active tubular secretion, and tubular reabsorption.

Answer: (D)

The main routes of drug elimination in urine are three processes that occur along the nephron: glomerular filtration, active tubular secretion, and tubular reabsorption. Filtration at the glomerulus lets free (unbound) drug pass into the filtrate, so only the unbound fraction is subject to this route. Active tubular secretion in the proximal tubule uses carrier proteins to move drugs from blood into the tubular fluid, adding to renal clearance beyond what filtration accomplishes. Tubular reabsorption then moves some drug from the filtrate back into the blood—often by passive diffusion for lipophilic or unionized drugs—reducing what gets excreted in urine. Together, these three pathways account for how drugs are eliminated in urine. The other options omit one or more of these important processes, which is why the full combination is the best answer.

The main routes of drug elimination in urine are three processes that occur along the nephron: glomerular filtration, active tubular secretion, and tubular reabsorption. Filtration at the glomerulus lets free (unbound) drug pass into the filtrate, so only the unbound fraction is subject to this route. Active tubular secretion in the proximal tubule uses carrier proteins to move drugs from blood into the tubular fluid, adding to renal clearance beyond what filtration accomplishes. Tubular reabsorption then moves some drug from the filtrate back into the blood—often by passive diffusion for lipophilic or unionized drugs—reducing what gets excreted in urine. Together, these three pathways account for how drugs are eliminated in urine. The other options omit one or more of these important processes, which is why the full combination is the best answer.