Which of the following antitubercular drugs can be safely used in severe renal failure?
**Core Concept**
The management of tuberculosis (TB) in patients with severe renal failure is challenging due to the potential nephrotoxicity of some antitubercular drugs. The choice of antitubercular drugs in such cases depends on their pharmacokinetics and the ability of the kidneys to eliminate them.
**Why the Correct Answer is Right**
Ethambutol is a bacteriostatic antitubercular agent that is primarily eliminated by the kidneys. However, it has a relatively low renal clearance, and its accumulation in the body is minimal even in patients with severe renal failure. This makes it a safer choice for patients with end-stage renal disease (ESRD) or those requiring dialysis. Moreover, ethambutol does not require dose adjustment in patients with renal impairment.
**Why Each Wrong Option is Incorrect**
**Option A:** Isoniazid is a prodrug that is metabolized to its active form, isonicotinic acid hydrazide, by the liver. However, its primary metabolite, hydrazine, is excreted by the kidneys. In patients with severe renal failure, the risk of isoniazid-induced peripheral neuropathy and other toxicities increases due to the accumulation of hydrazine.
**Option B:** Rifampicin is a potent inducer of the cytochrome P450 system and is primarily metabolized by the liver. However, its metabolites are excreted by the kidneys, and dose adjustment is required in patients with severe renal failure to prevent rifampicin-induced hepatotoxicity.
**Option C:** Pyrazinamide is a lipophilic compound that is primarily metabolized by the liver. However, its metabolites are excreted by the kidneys, and dose adjustment is required in patients with severe renal failure to prevent pyrazinamide-induced hepatotoxicity and urolithiasis.
**Clinical Pearl / High-Yield Fact**
In patients with severe renal failure, the use of antitubercular drugs that are primarily excreted by the kidneys, such as isoniazid and pyrazinamide, requires careful monitoring of drug levels and dose adjustment to prevent accumulation and toxicity.
**Correct Answer:** C. Pyrazinamide