Pharmacokinetics of docetaxel and ritonavir after oral administration of ModraDoc006/r in patients with prostate cancer versus patients with other advanced solid tumours

Purpose ModraDoc006 is a novel oral formulation of docetaxel. The clearance of intravenous docetaxel is higher in medically castrated prostate cancer patients as compared to patients with other types of solid tumours. Oral docetaxel requires co-administration ritonavir (r), which might further impact the pharmacokinetics (PK). We now compare the PK of docetaxel and ritonavir between patients with Hormone Sensitive Prostate Cancer (HSPC), metastatic Castration-Resistant Prostate Cancer (mCRPC) and other metastatic solid tumours, treated on the same dose and weekly schedule of ModraDoc006/r. Methods The docetaxel and ritonavir PK were compared between four patient groups from three clinical phase I trials, including eight male and eight female patients with different types of solid tumours (study 1), seven patients with HSPC (study 2) and five patients with mCRPC (study 3). All patients were treated with ModraDoc006 30 mg and ritonavir 100 mg in the morning, followed by ModraDoc006 20 mg and ritonavir 100 mg in the evening (ModraDoc006/r 30–20/100–100). For comparative purposes, the PK of six mCRPC patients that received 30–20/200–100 in study 3 were also evaluated. Results The maximum plasma concentration ( C max ) was significantly lower for both docetaxel and ritonavir in the prostate cancer patients as compared to the patients with other types of solid tumours treated at ModraDoc006/r 30–20/100–100. The docetaxel area under the plasma concentration versus time curve (AUC) was significantly different at this dose, with a mean AUC 0-48 of 1359 ± 374 ng/mL*h ( N = 8) in female patients and 894 ± 223 ng/mL*h ( N = 8) in male patients with different solid tumours (study 1), 321 ± 81 ( N = 7) in HSPC (study 2) and 367 ± 182 ng/mL*h ( N = 5) in mCRPC (study 3). A similar pattern was observed for ritonavir. ModraDoc006/r 30–20/200–100 in six mCRPC patients led to a comparable ritonavir exposure as compared to the patients at 30–20/100–100 in study 1 and increased the docetaxel AUC 0–48 to 1266 ± 473 ng/mL*h ( N = 6). Conclusion The exposure to docetaxel and ritonavir was significantly lower in prostate cancer patients as compared to patients with other types of solid tumours, treated on ModraDoc006/r 30–20/100–100. An increase of the ritonavir dose increased the docetaxel exposure in mCRPC patients. Therefore, a different RP2D of ModraDoc006/r is pursued in castrated prostate cancer patients as compared to patients with other types of solid tumours. Trial r