Phase I trial of cremophor EL with bolus doxorubicin.

Cremophor EL (cremophor), a component of the paclitaxel formulation, can potentially reverse P-glycoprotein-associated multidrug resistance. A Phase I trial of cremophor as a 6-h infusion every 3 weeks was performed with bolus doxorubicin (50 mg/m2). The cremophor dose was escalated from 1 to 60 ml/m2. A standard paclitaxel premedication was given before cremophor. Using a bioassay, potentially active cremophor levels (> or = 1 microl/ml) were measured in plasma from patients receiving cremophor doses of 30, 45, and 60 ml/m2. A cross-over design was used to assess the influence of cremophor 30 ml/m2 on the pharmacokinetics of doxorubicin and doxorubicinol. The plasma area under the concentration versus time curve (AUC) of doxorubicin increased from 1448 +/- 350 to 1786 +/- 264 ng/ml x h (P = 0.02) in the presence of cremophor, whereas the AUC of doxorubicinol increased from 252 +/- 104 to 486 +/- 107 ng/ml x h (P = 0.02). This pharmacokinetic interaction was associated with significantly increased neutropenia. With reduction of the doxorubicin dose to 35 mg/m2, the cremophor dose was increased to 60 ml/m2. Dose-limiting toxicities occurred in two of six patients after 45 ml/m2 and two of four patients after 60 ml/m2, which included febrile neutropenia and grade III cremophor-related toxicities of rash, pruritus, headache, and hypotension. All patients who received 45 ml/m2 cremophor reached plasma levels > or = 1.5 microl/ml, but at 60 ml/m2, only two of four reached this level, and the calculated plasma clearance of cremophor was significantly faster at this dose. One patient with hepatoma resistant to epirubicin achieved a near-complete response. Cremophor 45 ml/m2 over 6 h with 35 mg/m2 doxorubicin is recommended for further studies. The pharmacokinetic interaction between cremophor and doxorubicin is quantitatively similar to that described in trials of paclitaxel with doxorubicin and suggests that the cremophor in the paclitaxel formulation is responsible.