Background: Previous pharmacokinetic studies with docetaxel have mostly used 3-weekly (75 mg/m2 and 100 mg/m2) or weekly regimens (35-40 mg/m2). The pharmacokinetics and radiosensitizing efficacy of weekly 20 mg/m2 docetaxel, has however not been well characterized. We examined the pharmacokinetics of weekly docetaxel when administered with concurrent radiotherapy and compared the results with a 3-weekly 100 mg/m2 regimen.
Methods: Thirty-four patients with non small cell lung cancer (NSCLC) were included in this study, 19 receiving 100 mg/m2 docetaxel 3-weekly as single therapy, and 15 receiving 20 mg/m2 docetaxel weekly with concurrent radiotherapy. A newly developed HPLC method was used for measuring docetaxel levels, capable of quantifying docetaxel in plasma down to the nanomolar level.
Results: The HPLC method showed detectable concentrations of docetaxel in plasma even after 72 hours. In the present study we have demonstrated that median docetaxel plasma levels of 3 nM can be obtained 72 hours after a dose of 20 mg/m2.
Conclusion: The pharmacokinetics of docetaxel is characterized by great inter-individual variability and at some time points plasma concentrations for 20 mg/m2 and 100 mg/m2 docetaxel were overlapping. Extrapolation of these results indicates that radio sensitizing docetaxel concentrations may be present for as long as 1 week, thus supporting the use of 20 mg/m2 weekly docetaxel.