Effects of Altered Formulation on the Bioequivalence of Tacrolimus in Healthy Female and Male Volunteeers

Overview

Amorphous solid dispersion (ASD) formulations are increasingly used by the pharmaceutical industry to develop poorly water-soluble drugs into effective oral dosage forms. Examples include the antifungal drug itraconazole, the HIV protease inhibitor combination, lopinavir/ritonavir and the immunosuppressive, tacrolimus. There is potential for significant variation in bioavailability of ASD and thus heightened concern regarding the therapeutic efficacy as generic versions of these poorly water-soluble compounds become approved. The variation in bioavailability is to be expected because of our limited understanding of the precise physical chemistry of drug polymer amorphous solid dispersion formulations.

The specific aim is to conduct a randomized, single dose, four-treatment, four-period cross-over bioequivalence (BE) study in 24 healthy normal adult volunteers (males and non-gravid females) to evaluate the in vivo performance of fresh and aged brand name and generic amorphous solid dispersion (ASD) preparations of tacrolimus. The pharmacokinetics of tacrolimus as fresh Prograf® and aged Prograf®, fresh generic tacrolimus capsules and aged generic tacrolimus capsule will be determined and compared in healthy volunteers. The hypothesis to be tested is that the tacrolimus in the amorphous solid dispersion formulation will be partially crystalized upon treatment with controlled heat and humidity and will demonstrate lower absorption (lower relative bioavailability) compared to the fresh product. Moreover, the expectation is that the heat- and humidity-stressed generic formulations will not be robust to crystallization as the stressed brand name drug and will demonstrate a decreased in vivo performance and loss of bioequivalence. A total of 24 healthy female and male volunteers (age 18 to 49 years old) will be recruited to participate in this study. Volunteers will be determined to be free of significant medical conditions as assessed by medical history, physical examination, and blood and urine tests. Volunteers will be randomly allocated to receive one of the four treatment sequence groups and, on each occasion, receive one of the following: Fresh Prograf (RLD), fresh generic tacrolimus, 10-30% crystallized generic (Low Crystal), and 40-60% crystallized generic (High Crystal) tacrolimus. There will be a minimum 2-week washout between treatments. On each occasion, healthy volunteers will be administered tacrolimus, 5 mg, as a single capsule orally on an empty stomach with approximately 240 mL of water. Blood samples will be collected from the indwelling venous catheter (∼10 ml) after 0.5, 1, 2, 3, 4, 6, 8, 12 and 24 hours after dosing. Subjects will be regularly monitored during this time. The volunteers will be allowed to eat a normal lunch 3 hours after taking their tacrolimus dose. The primary endpoints will be the maximum blood concentration (Cmax) and the area under the curve (AUC) from zero to 24 hours and the AUC extrapolated from zero to infinity for tacrolimus for this bioequivalence study as recommended by the FDA guidance for industry. We will compute the AUC (from zero to 24 hours) to the last time point with measurable concentration using the linear trapezoidal rule and the AUC from time zero to time infinity with extrapolation computed as the quotient of the last measurable concentration and the terminal slope of the log concentration vs. time curve. In addition, we will report half-life of tacrolimus estimated from the terminal slope of the concentration vs. time plot determined by linear least squares regression. The peak blood tacrolimus concentration (Cmax,) and the time to Cmax (Tmax,) will be determined by visual inspection of the individual subject concentration-time curves. A treatment will be considered bioequivalent if the geometric least square mean ratios and 90% confidence interval for Cmax and AUC fall between 0.80 to 1.25 of the fresh Prograf®.