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Adverse drug events associated with the antidotes for toxic alcohol poisoning : a comparison of ethanol and fomepizole Lepik, Katherine Jean

Abstract

Background: The toxic alcohols methanol and ethylene glycol (antifreeze) can cause severe morbidity or death if ingested. Two antidotes are available for treatment: ethanol, which is inexpensive but has many adverse effects and fomepizole, which is expensive but allegedly safer. There are no comparative studies of these antidotes. Study objectives were to characterize the adverse drug events (ADEs) associated with ethanol and fomepizole and to compare the ADE rates between antidotes. Methods: This retrospective cohort study included patients ≥13 years hospitalized for toxic alcohol poisoning and treated with at least one dose of antidote between 1996-2005. Charts from ten B.C. hospitals were double reviewed by abstractors. Potential ADEs were evaluated by a consensus panel of three toxicologists. The primary outcome was any (i.e. at least one) ADE. Each poisoning incident contributed treatment-days from antidote start until either the onset of the first ADE or completion of antidote treatment. Time to event curves were generated by the Kaplan-Meier method. Cox regression was used to model the association between ADE rate and antidote type, using ethanol as the reference group. Results: After exclusions, there were 130 ethanol and 42 fomepizole treated incidents. Central nervous system ADEs occurred in 48% of ethanol and 2% of fomepizole treated incidents, cardiovascular ADEs in 7% ethanol and 1% fomepizole, gastrointestinal ADEs in 9% ethanol and 7% fomepizole. Ethanol was associated with minor hypoglycemia in 4%, phlebitis in 4% and diuresis in 6% of cases. The proportion of incidents with any ADE was 57% for ethanol and 12% for fomepizole. The unadjusted ADE rate (95% CI) per antidote treatment-day was 0.93 (0.87, 0.98) for ethanol and 0.13 (0.02, 0.24) for fomepizole. A significantly higher ADE rate for ethanol was evident within two hours after antidote start and was sustained throughout treatment. The Cox regression model adjusted for baseline severity of illness gave a rate ratio of 0.17 (0.07, 0.42), showing a six-fold reduction in A D E rate with fomepizole relative to ethanol. Discussion: Ethanol-related central nervous system effects accounted for most of the difference between treatment groups. The results suggest that fomepizole produces fewer ADEs than ethanol.

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