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

The patient's high urea and creatinine show renal failure. A drug's dose only needs to come down if the kidney is its main exit route. Let's go through the four anti-TB drugs.

1. INH: Cleared mostly by the liver, but a part of the load still leans on the kidney, so some caution is used in severe renal failure.
2. Rifampin: Cleared almost fully by the liver into bile. Kidney failure barely changes its blood level, so the usual dose can continue.
3. Pyrazinamide: Its breakdown products rely on the kidney for clearance, so they build up in renal failure and the dose must be trimmed.
4. Ethambutol: Leaves the body mostly unchanged through the kidney, so renal failure lets it pile up and raises the risk of eye toxicity, so the dose must be reduced.

Rifampin is the one drug whose main clearance route bypasses the kidney, so it alone needs no dose change.

Let's summarize:

• Liver-cleared drugs like rifampin stay safe at the usual dose in renal failure.
• Kidney-cleared drugs like pyrazinamide and ethambutol need a lower dose or longer interval.

The drug that needs no dose reduction here is rifampin.