Laboratory Tests

• Urine dipsticks for blood

• Urinalysis reveals more than 3 RBCs per high-power field—microscopic hematuria

• CBC with differential, PT/INR, aPTT, BUN, creatinine

Mesna is a thiol compound that is rapidly oxidized in the bloodstream after administration to dimesna, which is inactive. However, once filtered through the kidneys, dimesna is reduced back to mesna which binds to acrolein leading to inactiv-ation and excretion. The American Society of Clinical Oncology (ASCO) has published evidence-based guidelines for the dosing and administration of mesna (Table 99-12)46 The dose of oral mesna must be double the IV dose due to oral bioavailability between 40% and 50%. Because the half-life of mesna (approximately 1.2 hours) is much shorter than that of ifosfamide or cyclophosphamide, prolonged administration of mesna beyond the end of the chemotherapy infusion is critical (Fig. 99-2). Patients should receive at least 2 L of IV fluids beginning 12 to 24 hours before and ending 24 to 48 hours after the last dose of chemotherapy.

Hyperhydration with normal saline at 3 L/m /day with IV furosemide to maintain urine output greater than 100 mL/hour has also been used with cyclophosphamide. Continuous bladder irrigation by catheterization uses normal saline at 250 to 1,000 mL/hour to flush acrolein from the bladder. Mesna is equivalent to both strategies in patients receiving high-dose cyclophosphamide and avoids the discomfort and infection risk with catheterization and the intensity of hyperhydration. Thus, mesna is the preventative method of choice.

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