Abstract

The pharmacokinetics of cyclophosphamide (CYC) enantiomers were evaluated in patients with lupus nephritis distributed in 2 groups according to creatinine clearance: group 1 (90.6-144.6 mL/min/1.73 m(2)) and group 2 (42.8-76.4 mL/min/1.73 m(2)). All patients were treated with 0.75 to 1.3 g of racemic CYC as a 2-hour infusion and with 1 mg intravenous midazolam as a drug-metabolizing marker. CYC enantiomers and midazolam concentrations in plasma were measured by liquid chromatography/tandem mass spectrometry (LC/MS/MS). The following differences (Wilcoxon test, P < or = .05) were observed between the (S)-(-) and (R)-(+) enantiomers: AUC(0-infinity) 152.41 vs 129.25 microg.h/mL, CL 3.28 vs 3.89 L/h, Vd 31.38 vs 29.74 L, and t((1/2)) 6.79 vs 5.56 h for group 1 and AUC(0-infinity) 167.20 vs 139.08 microg.h/mL, CL 2.99 vs 3.59 L/h, and t((1/2)) 6.15 vs 4.99 h for group 2. No differences (Mann test, P < or = .05) were observed between groups 1 and 2 in the pharmacokinetic parameters of both enantiomers. No significant relationship was observed between midazolam clearance (2.92-16.40 mL/min.kg) and clearance of each CYC enantiomer. In conclusion, CYC kinetic disposition is enantioselective, resulting in higher exposures of the (S)-(-) enantiomer in lupus nephritis patients, and the pharmacokinetic parameters of both enantiomers are not altered by the worsening of renal condition.

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