Plasma drug concentration profile for MTX (A) and MP (B) monitored after 4 doses on maintenance cycles 1 (○), 2 (□), 4 (◊), and 6 (▵) in a single patient who was on a stable dose of 20 mg/m² of MTX and 75 mg/m² MP. The plots illustrate the greater intrapatient variability with MP.