The Correlation of Vinblastine Pharmacokinetics to Toxicity in Testicular Cancer Patients

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Abstract
The clinical pharmacokinetics of vinblastine administered by continuous 5-day infusion (3 mg/m2/day) was studied in 12 patients with primary testicular cancer. Serum vinblastine concentrations were determined by radioimmunoassay on serum collected over a 10-day period. Steady-state vinblastine concentrations were achieved within 60 to 108 hours (median, 72 hours). Vinblastine pharmacokinetics were analyzed and correlated to hematologic and nonhematologic toxicity. Hematologic toxicity was severe (granulocytopenia of less than 500/μL) in all patients; however, no correlation of vinblastine pharmacokinetics to duration of granulocytopenia or nadir was noted. Nonhematologic toxicity, however, showed a direct correlation to steady-state vinblastine concenations. Two distinct groups of patients were identified by a toxicity score evaluating nonhematologic toxicity: as low (group A) or high (group B). The toxicity score was calculated for each patient based on accumulated toxicity during the course of treatment. The mean toxicity score for all patients was 7.11 and for groups (A and B) it was 4.0 and 9.6, respectively (P = .02). Steady-state vinblastine concentration for each patient was compared with toxicity where the mean steady-state vinblastine concentration was 7.3 ng/mL for all patients, and 5.8 ng/mL and 8.5 ng/mL for groups A and B, respectively (P = .01). These steady-state vinblastine concentrations correlated directly with the mean toxicity scores revealing that patients with high steady-state vinblastine concentrations demonstrated more nonhematologic toxicity. Application of these data to pharmacokinetically directed studies are warranted to investigate this relationship and designate dosages of vinblastine to avoid excessive toxicity.