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[Irinotecan pharmacokinetics]
G G Chabot1, J Robert, F Lokiec
1Hôpital Saint-Louis, Centre Hayem, Inserm U, Paris.
Bulletin Du Cancer
|February 5, 1999
Summary
Irinotecan (CPT11) pharmacokinetics show dose-proportional increases in drug levels and significant correlations between drug exposure and toxicity, such as neutropenia and diarrhea. Understanding these relationships aids in optimizing CPT11 treatment for individual patients.
Area of Science:
- Pharmacology and Toxicology
- Drug Metabolism and Pharmacokinetics
- Clinical Oncology
Background:
- Irinotecan (CPT11) is a key chemotherapeutic agent, but its clinical use is limited by significant interpatient variability in pharmacokinetics and pharmacodynamics.
- Understanding the disposition and metabolism of CPT11 and its active metabolite SN38 is crucial for optimizing therapeutic outcomes and managing toxicities.
Purpose of the Study:
- To characterize the clinical pharmacokinetics of irinotecan (CPT11) and its active metabolite SN38.
- To investigate the relationship between irinotecan pharmacokinetics and clinical outcomes, including toxicity and tumor response.
Main Methods:
- Pharmacokinetic analysis using a 2 or 3 compartment model.
- Quantification of irinotecan and SN38 plasma concentrations over time.
- Assessment of drug-protein binding and metabolic pathways (carboxyesterase, UGT1A1, CYP3A4).
- Correlation analysis between pharmacokinetic parameters (AUC) and clinical endpoints (toxicity, response).
Main Results:
- Irinotecan exhibits a terminal half-life of 12 hours, volume of distribution of 168 L/m², and total body clearance of 15 L/m²/h.
- Plasma concentrations (AUC) of irinotecan and SN38 increase proportionally with dose, despite significant interpatient variability.
- SN38, 100-1000 fold more cytotoxic than irinotecan, circulates at lower concentrations but is highly protein-bound.
- Significant correlations were observed between irinotecan/SN38 AUCs and leuko-neutropenia and diarrhea.
- Tumor responses in Phase I trials suggest a dose-response relationship.
Conclusions:
- Irinotecan pharmacokinetics are characterized by dose proportionality and significant interpatient variability.
- Pharmacokinetic-pharmacodynamic relationships link drug exposure to toxicity (neutropenia, diarrhea) and potentially tumor response.
- These findings support individualized dosing strategies for irinotecan to improve clinical management, optimize toxicity control, and predict patient response.