Most important side effect of ethambutol is :
**Core Concept**
Ethambutol is an antitubercular medication that primarily works by inhibiting the synthesis of the bacterial cell wall, specifically by targeting the enzyme arabinosyl transferase, which is essential for the incorporation of arabinose into the mycobacterial cell wall. This leads to the disruption of the bacterial cell wall structure and ultimately, the death of the bacteria.
**Why the Correct Answer is Right**
The most significant side effect of ethambutol is optic neuritis, which can lead to visual disturbances, including decreased visual acuity, color blindness, and even blindness in severe cases. This occurs due to the drug's ability to cross the blood-brain barrier and affect the optic nerve. Ethambutol's effect on the optic nerve is dose-dependent, and patients on high doses are at a higher risk of developing this side effect.
**Why Each Wrong Option is Incorrect**
**Option A:** Nausea and vomiting are common side effects of many medications, including ethambutol, but they are not the most important side effect of this drug.
**Option B:** Hepatotoxicity is a potential side effect of many antitubercular medications, but it is not the most significant concern with ethambutol.
**Option C:** Hypersensitivity reactions can occur with many medications, but they are not the most important side effect of ethambutol.
**Clinical Pearl / High-Yield Fact**
To remember the side effect profile of ethambutol, use the mnemonic "EYES": Ethambutol can cause optic neuritis, Yellow vision, and eventually, blindness. This will help you recall the most important side effect of this medication.
**Correct Answer: C. Optic neuritis.**