Question

A patient with hypertension has a serum urea of 55 mg/dL and serum creatinine of 5.6 mg/dL, indicating renal failure. Which of the following anti-tubercular drugs does NOT require the dose to be reduced in this patient?

• A. INH
• B. Rifampin
• C. Pyrazinamide
• D. Ethambutol

Hint:

Ask which drug is cleared by the liver and bile rather than the kidney.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The patient has renal failure, shown by the high urea and creatinine. We need to find which anti-tubercular drug can be given at its normal dose without adjusting for poor kidney function.

Step 2: Key Concept:
A drug needs its dose lowered in renal failure only if the kidney is its main route of clearance. If a drug is cleared mainly by the liver and bile, poor kidney function does not cause it to build up, so the normal dose stays safe.

Step 3: Detailed Explanation:
Rifampin is cleared almost entirely through the liver into bile, then out in the stool. Kidney function barely affects its levels, so no dose change is needed even in advanced renal failure.
INH is mostly broken down by the liver too, but a meaningful part of its metabolite load still depends on kidney clearance in slow acetylators, so caution and sometimes a lower dose is advised in severe renal failure.
Pyrazinamide is handled by the kidney to a large extent, and its metabolites build up in renal failure, raising the risk of toxicity, so its dose or dosing interval must be adjusted.
Ethambutol is excreted largely unchanged by the kidney. In renal failure it accumulates and raises the risk of optic neuritis, so its dose must be reduced or the interval extended.

Step 4: Final Answer:
Since rifampin clears through the liver and bile, it needs no dose reduction in renal failure.