Virtual Bioequivalence Assessment of Elagolix Formulations Using Physiologically Based Pharmacokinetic Modeling.

In lieu of large bioequivalence studies and exposing healthy postmenopausal women to additional drug exposure for elagolix coadministered with hormonal add-back therapy, physiologically based pharmacokinetic (PBPK) modeling was used with in vitro dissolution data to test for virtual bioequivalence. For endometriosis, elagolix is approved at doses of 150 mg once daily and 200 mg twice daily as a tablet. As a combination therapy, two individual tablets, consisting of an elagolix tablet and an estradiol/norethindrone acetate 1/0.5 mg (E2/NETA) tablet, were utilized in Phase 3 endometriosis trials. However, the commercial combination drug products consist of a morning capsule (containing an elagolix tablet and E2/NETA tablet as a fixed-dose combination capsule, AM capsule) and an evening capsule (consisting of an elagolix tablet, PM capsule). In vitro dissolution profiles were dissimilar for the tablet and capsule formulations; thus, in vivo bioequivalence studies or a bioequivalence waiver would have been required. To simulate virtual cross-over, bioequivalence trials, in vitro dissolution data was incorporated into a previously verified PBPK model. The updated PBPK model was externally validated using relevant bioequivalence study data. Based on results of the virtual bioequivalence simulations, the commercial drug product capsules met the bioequivalence criteria of 0.80-1.25 when compared to the reference tablets. This was a novel example where PBPK modeling was utilized along with in vitro dissolution data to demonstrate virtual bioequivalence in support of a regulatory bioequivalence waiver.