Background: We previously found 70 mg flat-dose docetaxel coadministered with ketoconazole to modulate CYP3A4 to be the maximum tolerated dose that resulted in comparable docetaxel area under the plasma concentration-time curve (AUC) as 75-100 mg/m² docetaxel.
Patients and methods: We compared cycle 1 docetaxel pharmacokinetics and pharmacodynamics between ketoconazole-modulated (70 mg flat-dose docetaxel, n = 31) and conventional-dosed docetaxel (75 mg/m², n = 51) in chemonaive breast cancer patients in two sequential phase II studies.
Results: Ketoconazole-modulated docetaxel resulted in reduced docetaxel clearance (22.05 ± 8.29 versus 36.52 ± 13.39 l/h, P < 0.001), similar docetaxel AUC (3.93 ± 2.77 versus 3.77 ± 2.70 mg/l·h, P = 0.794) and tumor efficacy (cycle 1 responder 52% versus 55%) and less day 8 neutrophil suppression (1.24 ± 1.02 × 10⁹/l versus 0.47 ± 0.56 × 10⁹/l, P < 0.001), grade 4 neutropenia (32.3% versus 72.0%, P < 0.001) and febrile neutropenia (3.2 versus 23.5%, P = 0.015), compared with conventional-dosed docetaxel. Chinese had the lowest docetaxel clearance, highest AUC and most myelosuppression, followed by Malays and Indians, in response to ketoconazole-modulated docetaxel, while no significant interethnic differences were observed with conventional-dosed docetaxel.
Conclusions: Ketoconazole-modulated docetaxel achieved similar docetaxel AUC and tumor efficacy but reduced neutrophil suppression and febrile neutropenia at ∼40% reduced dose, representing a feasible alternative to conventional-dosed docetaxel. Interethnic differences in CYP3A4 inhibition by ketoconazole exist and are important when evaluating the impact of concomitant medications.
Trial registration: ClinicalTrials.gov NCT00212082 NCT00212095.