ATT causing orange colour urine is –
**Core Concept**
The question is testing the student's knowledge of a specific side effect of the antibiotic trimethoprim-sulfamethoxazole (TMP-SMX), also known as co-trimoxazole or Bactrim. The side effect in question is the characteristic orange discoloration of the urine, which is a notable clinical feature of TMP-SMX therapy.
**Why the Correct Answer is Right**
Trimethoprim-sulfamethoxazole is a sulfonamide antibiotic that can cause a harmless but noticeable side effect known as sulfonamide-induced chromaturia. This occurs due to the excretion of the antibiotic's metabolites, such as sulfamethoxazole's glucuronide conjugate, which binds to urobilin and other porphyrins in the urine, resulting in a characteristic orange or amber color. This phenomenon is not unique to TMP-SMX and can be seen with other sulfonamides.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the question, as it does not mention a known side effect of TMP-SMX.
**Option B:** This option is incorrect because the correct answer is a direct consequence of the antibiotic's pharmacokinetics and metabolism, not a side effect of another medication.
**Option C:** This option is incorrect because it is a different class of antibiotics altogether and does not cause the characteristic orange urine discoloration.
**Clinical Pearl / High-Yield Fact**
When encountering a patient on TMP-SMX therapy, be aware of this harmless but distinctive side effect, which can be a useful clinical clue in the differential diagnosis of urinary tract infections or other conditions.
**Correct Answer:** D. Sulfonamide-induced chromaturia.