Which of the following anti-tubercular drug is associated with red-green color blindness?
**Core Concept**
Ethambutol, a first-line antitubercular drug, can cause optic neuritis leading to visual disturbances, including red-green color blindness. This is due to its toxic effects on the optic nerve, specifically the retinal ganglion cells.
**Why the Correct Answer is Right**
Ethambutol inhibits the synthesis of mycolic acid in Mycobacterium tuberculosis, thereby exerting its antibacterial effects. However, one of its major side effects is optic neuritis, which can result in visual field defects, loss of color vision, and even blindness. The red-green color blindness associated with ethambutol is due to the selective damage to the retinal ganglion cells, particularly those responsible for transmitting red and green color information. Regular monitoring of visual acuity and color vision is essential when using ethambutol in patients.
**Why Each Wrong Option is Incorrect**
**Option A:** Isoniazid is associated with peripheral neuropathy and hepatitis, but not red-green color blindness.
**Option B:** Rifampicin can cause liver toxicity and interact with other medications, but it is not linked to visual disturbances.
**Option D:** Pyrazinamide can cause hepatotoxicity and arthralgias, but it is not associated with red-green color blindness.
**Clinical Pearl / High-Yield Fact**
When prescribing ethambutol, monitor patients regularly for signs of optic neuritis, including visual disturbances, loss of color vision, and changes in visual acuity. This is a classic exam trap, and students should remember that ethambutol is the only antitubercular drug associated with red-green color blindness.
**Correct Answer:** C. Ethambutol.