An orally bioavailable combination agent containing docetaxel, a second generation taxane, and ritonavir, a cytochrome P450 (CYP) 3A4 inhibitor, with potential enhanced antineoplastic activity. Docetaxel binds to and stabilizes tubulin, thereby inhibiting microtubule disassembly which results in cell-cycle arrest at the G2/M phase and cell death. Docetaxel is metabolized by CYP3A4 enzymes which is inhibited by the presence of ritonavir. This increases the plasma concentration of docetaxel and may increase docetaxel's efficacy.