Cisplatin is an essential part of testicular cancer treatment. We investigated whether long-term exposure to circulating platinum (Pt) plays a role in the development of late effects in survivors. We assessed Pt decay in samples collected 1–13 years after chemotherapy. Renal function is a strong determinant of exposure to Pt. Higher exposure to Pt is associated with an increased prevalence of adverse effects hypogonadism and hypertension.
The toxicity and pharmacokinetic properties of a drug determine whether hemodialysis and/or hemoperfusion are indicated in acute intoxications. Valproic acid is considered unremovable by hemodialysis because of the high protein binding of 90%-95%. A 27-year-old male with a history of seizures was admitted to the emergency room because of coma, hypernatriemia, and respiratory failure caused by an intoxication with a large dose of valproic acid. At admission, the plasma valproic acid level was 1414 mg/L (9.9 mmol/L) (therapeutic range: 50-100 mg/L (350-700 micromol/ L). The anion gap was 26 mmol/L (normal <12-14 mmol/L) and corresponded fairly well with this valproic acid level. Because of the potential toxicity of this high valproic acid level serial hemodialysis and hemoperfusion was performed. The first session was done with a charcoal column and the second session with a resin column. The patient recovered during the course of treatment. The valproic acid plasma clearances during treatment were: 80 mL/min (hemodialysis); 40 mL/min (hemoperfusion by charcoal) and 80 mL/min (hemoperfusion by resin, only in the first hour). The protein binding of valproic acid in plasma was only 32% at the start and was 54% at the end of the two sessions. In this specific case of a severe valproic acid intoxication, saturated protein binding resulted in an increased fraction of unbound valproic acid. This made hemodialysis an effective treatment, while hemoperfusion was relatively less effective because of saturation of the column. In conclusion, the toxicokinetics of valproate are quite different from the pharmacokinetics at therapeutic levels. The anion gap and protein binding are important parameters in toxicokinetics.
Vincristine (VCR) has been widely used to treat childhood malignancies for over thirty years, but its plasma disposition has not yet been well-defined. Therefore, we conducted a pharmacokinetic study of VCR in 17 children with acute lymphoblastic leukemia (ALL) receiving the first dose of VCR. A new high-performance liquid chromatographic assay was used for the measurement of VCR in plasma. A two-compartment pharmacokinetic model was fit to the data by nonlinear least-squares regression. Estimated pharmacokinetic parameters were highly variable; mean (S.D.) volume of distribution at steady-state was 360 (176) L.m-2; total body clearance was 431 (238) ml.min-1.m-2, and elimination half-life was 823 (390) min. These results were compared to data from eight adults with lung cancer. Mean volume of distribution in adults and children were similar, but VCR clearance was significantly larger in children (P = 0.01), resulting in a significantly longer elimination half-life in the adults (P < 0.01). We conclude that administration of a standard dosage of VCR to children with ALL results in a highly variable systemic drug exposure, which may have implications for the oncolytic effect and/or toxicity in individual patients. Comparison of data from children and adults suggests that VCR elimination rate is a function of age; this could account for more severe neurotoxicity in older patients. However, it cannot be excluded that differences between the children and adults may be due to other variables than age. Future studies should focus on the possible influence of multidrug resistance modulating agents on VCR pharmacokinetics and on pharmacokinetic-pharmacodynamic relationships in individual patients.
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