Which of the following disease modifying anti–rheumatoid drugs is a prodrug ?
**Core Concept**
Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by inflammation and joint destruction. Disease-modifying anti-rheumatoid drugs (DMARDs) are used to modify the disease course by suppressing the immune system. Prodrugs are pharmacologically inactive compounds that require metabolic conversion to an active drug.
**Why the Correct Answer is Right**
A prodrug of a DMARD is a compound that requires metabolic activation to produce the active drug. In the case of methotrexate, it is a prodrug that is converted to its active form, 7-hydroxymethotrexate, by dihydrofolate reductase. This active form then inhibits dihydrofolate reductase, leading to a decrease in the synthesis of tetrahydrofolate and subsequently, a decrease in the production of DNA and RNA. This mechanism ultimately leads to the suppression of the immune system and a decrease in inflammation.
**Why Each Wrong Option is Incorrect**
**Option A:** Leflunomide is a DMARD that works by inhibiting pyrimidine synthesis, but it is not a prodrug. It is metabolized to its active form, teriflunomide, which inhibits dihydroorotate dehydrogenase.
**Option B:** Sulfasalazine is a DMARD that works by inhibiting the production of inflammatory mediators, but it is not a prodrug.
**Option C:** Cyclosporine is an immunosuppressant that works by inhibiting calcineurin, but it is not a DMARD or a prodrug.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that prodrugs like methotrexate require careful monitoring of liver function and folate levels to avoid adverse effects.
**Correct Answer: A. Methotrexate**