Urinary excretion of ifosfamide, 4-hydroxyifosfamide, 3- and 2-dechloroethylifosfamide, mesna, and dimesna in patients on fractionated intravenous ifosfamide and concomitant mesna therapy

Abstract

The oxazaphosphorine antineoplastic ifosfamide (IF) is metabolized by two different initial pathways: ring oxidation ("activation"), forming 4-OH-IF ("activated IF"), and side-chain oxidation with liberation of chloroacetaldehyde (CAA), forming the inactive metabolites 3-dechloroethylifosfamide or 2-dechloroethylifosfamide (3-DCE-IF, 2-DCE-IF). 4-OH-IF and 4-OH-IF-derived acrolein are thought to be responsible for IF-induced urotoxicity (hemorrhagic cystitis), whereas CAA may be involved in IF-associated nephrotoxicity (renal tubular damage). The thiol compound 2-mercaptoethane sulfonate sodium (mesna) has proved to inactivate sufficiently the urotoxic metabolites of oxazaphosphorine cytostatics and is therefore routinely given to patients receiving IF chemotherapy. The cumulative urinary excretion of IF, 4-OH-IF, 3-DCE-IF, 2-DCE-IF, mesna, and its disulfide dimesna was studied in 11 patients with bronchogenic carcinoma receiving IF on a 5-day divided-dose schedule (1.5 g/m2 daily) with concomitant application of mesna (0.3 g/m2 at 0,4, and 8 h after IF infusion). On day 1 the mean cumulative 24-h urinary recoveries (percentage of the IF dose) recorded for IF, 4-OH-IF, 3-DCE-IF, and 2-DCE-IF were 13.9%, 0.52%, 4.8%, and 1.5%, respectively. On day 5 the corresponding values were 12.2%, 0.74%, 9.9%, and 3.6%, respectively. This time-dependent increase in urinary excretion of IF metabolites, which is caused by rapid autoinduction of hepatic oxidative metabolism, may result in a higher probability for the development of urotoxic and nephrotoxic side effects during prolonged IF application. The mean 24-h urinary recoveries (percentage of the daily mesna dose) recorded for mesna/dimesna on day 1 (day 5) were 23.8%/45.2% (21.2%/39.8%), respectively. The mean molar excess of urinary reduced ("free") mesna over 4-OH-IF ranged from 11 to 72 on day 1 and from 6 to 40 on day 5. This indicates that although urinary excretion of 4-OH-IF rises with repeated IF application, mesna in standard doses should sufficiently inactivate the urotoxic IF metabolites.