Influence of multiple dose activated charcoal on the disposition kinetics of irinotecan in rats

The main clinical adverse effect of irinotecan (CPT-11) therapy is diarrhoea. Using a rat model, we attempted to study the effects of activated charcoal on the prevention of diarrhoea after a bolus dose of CPT-11, and also investigated the disposition kinetics of CPT-11 and its metabolite, SN-38, as well as SN-38 glucuronide (SN-38G) in the presence and absence of charcoal.

Male Sprague-Dawley rats were given a daily oral dose of activated charcoal (Ultracarbon, 2.5 g/kg daily for 5 days) 10 min before an i.v. bolus injection of CPT-11 (60 mg/kg daily for 5 days; total dose 300 mg/kg); the control group was given CPT-11 alone. The pharmacokinetics of CPT-11, SN-38 and SN-38G were determined in both groups of rats on day 1. The incidence of diarrhoea was monitored throughout the course of the study.

There were no differences in the mean (+/- SD) C, (15.8 +/- 7.5 vs 12.1 +/- 3.3 microg/ml), t1/2 (2.2 +/- 0.7 vs 2.2 +/- 0.5 h), CL (5.7 +/- 2.1 vs 6.8 +/- 1.2 l/h/kg), Vd (1798 +/- 958 vs 2280 +/- 731 l/kg) or AUC0-infinity (11.8 +/- 3.9 vs 9.1 +/- 1.7 microg x h/ml) of CPT-11 after dosing with or without activated charcoal. Similarly, charcoal treatment had no effect on the disposition kinetics of SN-38 and SN-38G. A higher frequency of grade 3 diarrhoea was observed in the control group compared to the charcoal treatment group (log OR: -1.06; 95% CI: -2.25, 0.13) but this was only marginally statistically significant (p = 0.08).

These results suggest that multiple oral doses of activated charcoal do not modulate the clearance of CPT-11 and SN-38 in rats. The implication is that activated charcoal alone may not be very effective in preventing CPT-11-induced diarrhoea.