Optimizing the Absorption of Valspodar, a P-glycoprotein Modulator, Part II: Quantifying its Pharmacokinetic Variability and Refining the Bioavailability Estimate

A randomized, sequential, bioreplication study was performed with 24 healthy volunteers to assess the pharmacokinetic variability of oral and intravenous administrations of valspodar, a multidrug resistance modulator for use as a chemotherapy adjunct. Subjects received 200 mg as a 2-hour intravenous infusion and 400 mg orally as microemulsion soft gelatin capsules each given on two separate occasions. Following replicate intravenous administrations, reproducibility in peak concentration and area-under-the-curve was demonstrated by interoccasion equivalence testing. Low to moderate inter- and intra-subject pharmacokinetic variability were observed with coefficients of variation ranged from 9% to 19%. Absolute bioavailability from the microemulsion formulation was 60%. Replicate oral administrations demonstrated uniform and repeatable absorption with interoccasion equivalence in peak concentration, time to reach the peak concentration, and area-under-the-curve. Coefficients of inter- and intra-subject variation for these parameters ranged from 10% to 20% indicating low to moderate pharmacokinetic variability. When variabilities were compared between the two routes of administration, the absence of differences indicated that the rate and extent of drug absorption from the microemulsion formulation was as uniform and repeatable as by intravenous infusion.