A patient, diagnosed with rheumatoid arthritis, was on medications. After 2 years, developed blurring of vision and was found to have corneal opacity. Which of the following drug most likely causes that?
**Core Concept**
Rheumatoid arthritis (RA) patients are often treated with disease-modifying antirheumatic drugs (DMARDs), which may have systemic side effects. One such side effect is drug-induced ocular toxicity, particularly affecting the cornea.
**Why the Correct Answer is Right**
The drug most likely responsible for the patient's symptoms is Methotrexate (MTX). MTX is a commonly used DMARD in RA treatment, and its long-term use can lead to ocular toxicity, characterized by corneal epithelial toxicity and subsequent corneal opacity. This occurs due to MTX's inhibitory effect on the enzyme dihydrofolate reductase (DHFR), which is crucial for the synthesis of thymidine, an essential nucleotide for corneal epithelial cell proliferation.
**Why Each Wrong Option is Incorrect**
**Option A:** Hydroxychloroquine is another DMARD used in RA treatment, but it is less commonly associated with corneal toxicity compared to MTX.
**Option B:** Leflunomide is a DMARD that may cause liver toxicity but is not typically linked to corneal opacity.
**Option C:** Sulfasalazine is a DMARD with gastrointestinal side effects but is not commonly associated with ocular toxicity.
**Clinical Pearl / High-Yield Fact**
When prescribing DMARDs for RA patients, it's essential to monitor for signs of ocular toxicity, particularly corneal epithelial changes, and consider regular ophthalmological assessments to prevent vision loss.
**Correct Answer:** C.