Purpose: Vismodegib, a first-in-class oral hedgehog pathway inhibitor, is an effective treatment for advanced basal cell carcinoma. Based on in vitro data, a clinical drug-drug interaction (DDI) assessment of cytochrome P450 (CYP) 2C8 was necessary; vismodegib's teratogenic potential warranted a DDI study with oral contraceptives (OCs).
Methods: This single-arm, open-label study included two cohorts of patients with locally advanced or metastatic solid malignancies [Cohort 1: rosiglitazone 4 mg (selective CYP2C8 probe); Cohort 2: OC (norethindrone 1 mg/ethinyl estradiol 35 μg; CYP3A4 substrate)]. On Day 1, patients received rosiglitazone or OC. On Days 2-7, patients received vismodegib 150 mg/day. On Day 8, patients received vismodegib plus rosiglitazone or OC. The effect of vismodegib on rosiglitazone and OC pharmacokinetic parameters (primary objective) was evaluated through pharmacokinetic sampling over a 24-h period (Days 1 and 8).
Results: The mean ± SD vismodegib steady-state plasma concentration (Day 8, N = 51) was 20.6 ± 9.72 μM (range 7.93-62.4 μM). Rosiglitazone AUC(0-inf) and C(max) were similar with concomitant vismodegib [≤8% change in geometric mean ratios (GMRs); N = 24]. Concomitant vismodegib with OC did not affect ethinyl estradiol AUC(0-inf) and C(max) (≤5% change in GMRs; N = 27); norethindrone C(max) and AUC(0-inf) GMRs were higher (12 and 23%, respectively) with concomitant vismodegib.
Conclusions: This DDI study in patients with cancer demonstrated that systemic exposure of rosiglitazone (a CYP2C8 substrate) or OC (ethinyl estradiol/norethindrone) is not altered with concomitant vismodegib. Overall, there appears to be a low potential for DDIs when vismodegib is co-administered with other medications.