**Question:** A patient with tuberculosis develops bright orange-red urine and calls his physician in a panic because he is afraid he is bleeding into the urine. The patient has no other urinary tract symptoms. Which of the following medications is most likely to produce this side effect?

A. Isoniazid
B. Ethambutol
C. Pyrazinamide
D. Rifampicin

**Correct Answer:**

**Core Concept:**

The correct answer is D. Rifampicin, a key drug in the treatment of tuberculosis, can cause a side effect called hematuria (blood in the urine). This is due to its direct toxic effect on the renal tubules and glomeruli, leading to damage and subsequent bleeding into the urine.

**Why the Correct Answer is Right:**

Rifampicin is a potent antibiotic that belongs to the rifamycin class of drugs. It is a key component of the anti-TB regimen, which includes isoniazid, pyrazinamide, and ethambutol. Hematuria is a rare but known side effect of rifampicin, which is due to its direct toxic effect on the renal tubules and glomeruli. This damage can cause cells and proteins to leak into the urine, resulting in blood-stained urine or hematuria.

**Why Each Wrong Option is Incorrect:**

A. Isoniazid is another critical drug in the treatment of tuberculosis but is less likely to cause hematuria compared to rifampicin. This is because isoniazid primarily targets mycobacteria and has a lower impact on renal tubules and glomeruli.

B. Ethambutol is another essential drug in the treatment of tuberculosis but is also less likely to cause hematuria compared to rifampicin. This is because ethambutol primarily targets mycobacteria and has a lower potential for renal toxicity.

C. Pyrazinamide is a key drug in the treatment of tuberculosis, but its side effects are generally milder than those of rifampicin. Pyrazinamide primarily targets mycobacteria and has a lower risk of causing renal tubular damage and hematuria compared to rifampicin.

**Clinical Pearl:**

Understanding the pharmacology of these medications is crucial when treating tuberculosis as it helps to recognize and manage potential side effects. In this case, recognizing hematuria as a side effect of rifampicin is essential for timely intervention and adjustment of treatment plan to minimize potential harm to the patient.