Prophylactic treatment of irinotecan-induced diarrhea with neomycin (a randomized, placebo-controlled, double-blind study)
3626 Background: Delayed-type diarrhea is a common side-effect of irinotecan, and is associated with a bacterial-mediated formation of the active irinotecan metabolite SN-38 from its glucuronide conjugate in the intestines. We hypothesized that concomitant administration of the aminoglycoside antibiotic neomycin would diminish exposure of the gut to SN-38, ameliorating the incidence of diarrhea. Methods: Patients were treated with irinotecan in a randomized, placebo-controlled, double-blind trial. In arm A, patients received irinotecan (350 mg/m2 i.v. for 90 minutes once every 3 weeks) combined with neomycin (660 mg orally 3 times daily for 3 consecutive days, starting 2 days before chemotherapy). In arm B, patients received the same irinotecan regimen with placebo. To detect a 50% reduction to less than grade 2 diarrhea (power=.80; P=.05), 60 patients had to be studied. Blood samples for additional pharmacokinetic and pharmacogenetic analyses were obtained after separate informed consent. Results: Sixty-two patients were evaluable for toxicity analysis. Relevant baseline patient characteristics (P>.06), SN-38 plasma concentrations (P=.80; N=43), and UGT1A1*28 genotype status (P=.58; N=52) were similar in both arms. Distribution, severity, and duration of diarrhea did not differ significantly between both arms (P>.32), although grade 3 diarrhea tended to be less frequent in the neomycin arm (45% reduction; P=.19). Grade 2 nausea was more common in this arm (39% vs. 9%; P<.01). The presence of at least one UGT1A1*28 allele was strongly related to the incidence of grade 2–3 diarrhea (69% vs. 34%; P=.01). Conclusions: Our results do not suggest a role for neomycin in the prophylactic treatment of irinotecan-induced diarrhea. In addition, neomycin does not influence systemic SN-38 pharmacokinetics. Also, it is suggested that each patient’s UGT1A1*28 genotype status could be used as a prospective screening tool to prevent severe diarrhea. No significant financial relationships to disclose.