Which parameter is essential to monitor hydration status during high-dose methotrexate therapy?

• A. Urine output
• B. Blood urea nitrogen alone
• C. Serum sodium only
• D. Heart rate alone

Answer: (A)

Maintaining adequate urine output is essential because high-dose methotrexate is cleared primarily by the kidneys, so good diuresis helps prevent MTX from precipitating in the renal tubules and reduces nephrotoxicity risk. Urine output provides a direct, real-time measure of hydration status and renal function, guiding fluid management and MTX clearance. Other indicators like BUN alone can be misleading since BUN is influenced by many factors (protein intake, liver function, MTX effects) and does not reflect current urine flow. Serum sodium alone and heart rate alone are not reliable hydration markers and can be affected by numerous non-hydration-related factors.