Which of the following antitubercular drugs can be safely used in severe renal failure :
**Core Concept**
The question is testing the safety and efficacy of antitubercular drugs in patients with severe renal failure. This requires knowledge of the pharmacokinetics and metabolism of these drugs, as well as their potential side effects and interactions.
**Why the Correct Answer is Right**
Ethionamide is a second-line antitubercular drug that is primarily metabolized by the liver and does not require renal excretion. This makes it a safer choice for patients with severe renal failure. Ethionamide works by inhibiting the synthesis of mycolic acid, a key component of the Mycobacterium tuberculosis cell wall.
**Why Each Wrong Option is Incorrect**
**Option A:** Isoniazid is primarily excreted by the kidneys and can accumulate to toxic levels in patients with renal failure, leading to peripheral neuropathy and other side effects.
**Option B:** Streptomycin is an aminoglycoside antibiotic that is excreted by the kidneys and can cause nephrotoxicity and ototoxicity in patients with renal failure.
**Option C:** Pyrazinamide is primarily excreted by the kidneys and can cause renal damage in patients with pre-existing renal disease.
**Clinical Pearl / High-Yield Fact**
When using antitubercular drugs in patients with renal failure, it is essential to monitor renal function closely and adjust doses accordingly. Ethionamide is a safer choice in this setting, but other drugs may require dose adjustments or alternative treatments.
**Correct Answer:** C.