Pharmacokinetic and pharmacodynamic evaluation of the topoisomerase inhibitor irinotecan in cancer patients.
OBJECTIVE
We conducted a pharmacokinetic and pharmacodynamic evaluation of irinotecan (CPT-11) and determined the effect of race and sex on disposition and toxicity of CPT-11. We tested the efficacy of acetaminophen (AAP) to phenotype SN-38 glucuronidation.


METHODS
Forty patients received a dose of 145 mg/m2 of CPT-11 as a 90-minute infusion. Total CPT-11, SN-38, and SN-38G were quantitated in plasma and urine samples. Following administration of 1 g AAP, urinary concentrations of AAP and AAP-glucuronide (AAP-G) were assessed.


RESULTS
CPT-11 exhibited a mean elimination half-life (t1/2) of 8.8 hours, an average clearance (CL) of 14.6 L/h/m2, and a mean volume of distribution at steady-state (Vdss) of 136 L/m2. SN-38 and SN-38G had low plasma availabilities (3% and 10% relative to CPT-11), with mean t1/2 values of 11.6 and 10.5 hours, respectively. Urinary recovery accounted for 15% of the dose. Race and sex had no effect on the plasma availability of CPT-11, SN-38, and SN-38G. The applicability of biliary index (BI) in predicting dose-limiting intestinal toxicity was validated. Patients who developed grade 3 or 4 toxicity had significantly higher index values compared with patients with grade 0 to 2 toxicity (P = .001). There was no difference in the incidence and severity of toxicity based on race and sex. AAP was a poor predictor of SN-38 glucuronidation.


CONCLUSIONS
The high degree of interpatient variability in parameter estimates suggests pharmacogenetic variation or differential induction or inhibition of the sequential metabolic pathway of CPT-11, as well as variability in transport systems. The low urinary recovery indicates substantial biliary excretion and supports the significant correlation between intestinal toxicity and BI. Black patients are not at increased risk of toxicity. An assessment of individual differences in SN-38 conjugation remains to be established.
Gupta
E
E
Department of Medicine, University of Chicago, IL, USA.
Mick
R
R
Ramirez
J
J
Wang
X
X
Lestingi
T M
TM
Vokes
E E
EE
Ratain
M J
MJ
D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics / Q000494:pharmacology*; D019540:Area Under Curve; D002166:Camptothecin / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D005260:Female; D006801:Humans; D000077146:Irinotecan; D008297:Male; D009369:Neoplasms / Q000097:blood / Q000378:metabolism* / Q000652:urine; D010641:Phenotype; D044469:Racial Groups / Q000235:genetics*; D012720:Severity of Illness Index; D012727:Sex Characteristics; D059004:Topoisomerase I Inhibitors
D000970:Antineoplastic Agents; D059004:Topoisomerase I Inhibitors; D000077146:Irinotecan; D002166:Camptothecin