Pharmacokinetics and toxicity of weekly docetaxel in older patients

Purpose: To evaluate the pharmacokinetics of weekly docetaxel in a cohort of older patients with metastatic cancer and to explore the relationship of pharmacokinetic variables, Erythromycin Breath Test results, age, geriatric assessment variables, and toxicity to therapy. Experimental Design: Twenty patients ages ≥65 years with metastatic breast, prostate, or lung cancer entered an Institutional Review Board - approved protocol to evaluate the pharmacokinetics of weekly docetaxel administered at 35 mg/m² i.v. for 3 weeks followed by a 1-week break. The Erythromycin Breath Test and geriatric assessment were done before the first dose. Blood samples were collected for pharmacokinetic analysis with the first dose of docetaxel. Results: Of the 20 patients who entered the study, 19 were evaluable. There were no age-related differences in the pharmacokinetics of weekly docetaxel. Fifty-eight percent (11 of 19) experienced grade ≥3 toxicity: 16% (3 of 19) grade ≥3 hematologic toxicity, and 53% (10 of 19) grade ≥3 nonhematologic toxicity. There was an association between the Erythromycin Breath Test results and docetaxel pharmacokinetic variables; however, there was no association between Erythromycin Breath Test results or docetaxel pharmacokinetics with frequency of grade ≥3 toxicity. Conclusions: Despite no statistically significant age-related differences in weekly docetaxel pharmacokinetics, over half of these older patients experienced a grade ≥3 toxicity at the 35 mg/m2 starting dose. We advocate a starting dose of 26 mg/m² on this weekly schedule and dose escalating if no toxicity.