During high-dose methotrexate therapy, which laboratory and organ-function tests are essential to monitor?

• A. Monitor MTX serum level, renal function (creatinine/BUN), liver enzymes, CBC, electrolytes, hydration status, urine output and uric acid.
• B. Monitor MTX serum level only.
• C. Monitor renal function only.
• D. Monitor liver enzymes and platelet count only.

Answer: (A)

High-dose methotrexate has a narrow window and relies on the kidneys to clear the drug, so you need to watch both how much methotrexate remains in the body and how the organs are handling it. Measuring MTX serum level lets you gauge how quickly clearance is progressing and guides the duration and intensity of leucovorin rescue to prevent toxicity. Renal function tests (creatinine and BUN) are essential because any decline in kidney function slows MTX clearance and increases the risk of severe toxicity. Liver enzymes are checked because the liver can be affected by methotrexate, signaling possible hepatotoxicity. A complete blood count reveals bone marrow suppression, a key toxic effect of MTX. Tracking electrolytes and hydration status, along with urine output, provides early signs of renal stress and fluid balance issues that can influence drug clearance and risk of crystal precipitation in the kidneys. Uric acid is monitored due to the risk of tumor lysis and related uric acid nephropathy, which can compound renal impairment during aggressive therapy. Together, this comprehensive monitoring captures drug levels, renal clearance, hepatic safety, marrow suppression, and fluid-electrolyte balance, all of which are crucial to safely administering high-dose MTX.