**Core Concept**
Methotrexate is a chemotherapeutic agent and immune system suppressant used in the treatment of various cancers and autoimmune diseases. Its mechanism of action involves the inhibition of dihydrofolate reductase (DHFR), an enzyme crucial for DNA synthesis and repair. Monitoring of certain parameters is essential to prevent methotrexate-induced toxicity.

**Why the Correct Answer is Right**
Methotrexate therapy requires close monitoring of liver function, renal function, and complete blood counts (CBC) to prevent hepatotoxicity, nephrotoxicity, and bone marrow suppression. Additionally, folic acid supplementation is often recommended to mitigate the risk of methotrexate-induced megaloblastic anemia. However, serum lactate dehydrogenase (LDH) levels are not a routine parameter monitored in patients on methotrexate therapy.

**Why Each Wrong Option is Incorrect**
**Option A:** Liver function tests (LFTs) are indeed monitored in patients on methotrexate therapy to assess hepatotoxicity.
**Option B:** Renal function tests are also crucial in monitoring the effects of methotrexate on kidney function.
**Option C:** Complete blood counts (CBC) are essential to detect bone marrow suppression and anemia.

**Clinical Pearl / High-Yield Fact**
Methotrexate-induced hepatotoxicity can be mitigated by administering folic acid supplementation and monitoring liver function tests regularly.

**Correct Answer:** D.