A middle aged old man, with chronic renal failure is diagnosed to have sputum-positive pulmonary tuberculosis. His creatinine clearance is 25ml/min. All of the following drugs need modification in doses except:
**Question:** A middle aged old man, with chronic renal failure is diagnosed to have sputum-positive pulmonary tuberculosis. His creatinine clearance is 25ml/min. All of the following drugs need modification in doses except:
A. Amikacin
B. Ethambutol
C. Isoniazid
D. Rifampicin
**Core Concept:**
In patients with chronic renal failure, drug dosing must be adjusted to avoid accumulation of toxic doses and ensure effective treatment. The creatinine clearance (CC) provides an estimate of the glomerular filtration rate (GFR), reflecting the kidneys' ability to filter blood. A decreased GFR indicates impaired renal function and requires dose adjustments of certain drugs used in the treatment of tuberculosis.
**Why the Correct Answer is Right:**
Amikacin is a nephrotoxic aminoglycoside antibiotic, meaning it can directly damage the kidneys and worsen renal function. Therefore, its dose needs to be adjusted in chronic renal failure patients.
**Why Each Wrong Option is Incorrect:**
- **Ethambutol:** Ethambutol is a bacteriostatic drug that primarily targets the Mycobacterium tuberculosis. There is no significant dose adjustment required based on renal function in patients with chronic renal failure.
- **Isoniazid:** Isoniazid is another bacteriostatic drug that primarily targets M. tuberculosis. No dose adjustments based on renal function are required in chronic renal failure patients.
- **Rifampicin:** Rifampicin is a bactericidal drug that targets the RNA polymerase of the bacteria, inhibiting DNA synthesis. Although rifampicin has a higher volume of distribution and a prolonged half-life in patients with impaired renal function, dose adjustments are not typically necessary, especially when the dose of the other TB drugs is adjusted appropriately.
**Clinical Pearl:**
In chronic renal failure patients, it is crucial to adjust the doses of drugs like Amikacin and other nephrotoxic medications, as their toxicity can worsen renal function. However, the doses of ethambutol, isoniazid, and rifampicin are typically not adjusted based on renal function, as long as the doses of other TB drugs are adjusted appropriately.
**Why the Correct Answer is Right:**
Amikacin, a nephrotoxic aminoglycoside antibiotic, requires dose adjustment in chronic renal failure patients due to its potential to damage the kidneys and worsen renal function.
**Why Each Wrong Option is Incorrect:**
- Ethambutol, Isoniazid, and Rifampicin do not need dose adjustment based on renal function in chronic renal failure patients. Their doses are adjusted along with other TB drugs, ensuring optimal treatment efficacy without compromising renal function.