Medication errors associated with the use of ethanol and fomepizole as antidotes for methanol and ethylene glycol poisoning.

INTRODUCTION: Little is known about medication errors which occur with the antidotes ethanol and fomepizole, used for treatment of methanol and ethylene glycol poisoning. Study objectives were to describe and compare the frequency, type, outcome and underlying causes of medication errors associated with ethanol and fomepizole. METHODS: Patients aged ≥13 years were included if they were hospitalized in 1996-2005 for methanol or ethylene glycol poisoning and treated with ethanol or fomepizole. Charts from 10 hospitals were separately reviewed by two abstracters who recorded case details. A consensus panel of clinicians used the abstracted data to identify medication errors and classify error outcome. Fisher's exact test determined significant differences in the proportion of ethanol and fomepizole-treated cases with medication error and univariate logistic regression identified risk factors associated with harmful dosage errors. RESULTS: There were 145 ethanol- and 44 fomepizole-treated cases. There was ≥1 medication error in 113/145 (78%) ethanol- and 20/44 (45%) fomepizole-treated cases (p = 0.0001) with more ethanol-related errors involving excessive dose, inadequate monitoring and inappropriate antidote duration. Harmful errors occurred in 19% of ethanol- and 7% of fomepizole-treated cases (p = 0.06) and were largely due to excessive antidote dose or delayed antidote initiation. Occurrence of harmful dosage error was reduced in cases with Poison Control Centre consultation, odds ratio (95% confidence interval) 0.39 (0.17, 0.91), hemodialysis 0.37 (0.16, 0.88), or fomepizole versus ethanol 0.24 (0.06, 1.04). CONCLUSION: Fomepizole was less prone to medication error than ethanol. Error-related harm was most commonly due to excessive antidote dose or delayed antidote initiation.

Adverse drug events associated with the antidotes for methanol and ethylene glycol poisoning: a comparison of ethanol and fomepizole.

STUDY OBJECTIVE: We investigate adverse drug events associated with antidotes ethanol and fomepizole in methanol or ethylene glycol poisonings. An "adverse drug event" is harm associated with normal or incorrect drug use. We describe type, frequency, severity, seriousness, and onset time of adverse drug events and test the hypothesis that fomepizole results in fewer adverse drug events than ethanol. METHODS: This cohort study included patients aged 13 years or older, hospitalized between 1996 and 2005 for methanol or ethylene glycol poisoning (identified by International Classification of Diseases, Ninth Revision or 10th Revision codes) and treated with at least 1 dose of ethanol or fomepizole. Two abstractors separately reviewed each chart, identifying new clinical events during antidote treatment. Three toxicologists determined, by consensus, which events were adverse drug events. The primary outcome was at least 1 adverse drug event, expressed as adverse drug event rate per person-day of antidote treatment. Association between time to first adverse drug event and antidote type was modeled by Cox regression, adjusted for confounders. RESULTS: Two hundred twenty-three charts were reviewed and 172 analyzed. Toxicologists identified at least 1 adverse drug event in 74 of 130 (57%) ethanol-treated and 5 of 42 (12%) fomepizole-treated cases. Central nervous system symptoms accounted for most adverse drug events (48% ethanol-treated, 2% fomepizole-treated). Severe adverse drug events occurred in 26 of 130 (20%) ethanol-treated (coma, extreme agitation, cardiovascular) and 2 of 42 (5%) fomepizole-treated (coma, cardiovascular). Serious (life-threatening) adverse drug events occurred in 11 of 130 (8%) ethanol-treated (respiratory depression, hypotension) and 1 of 42 (2%) fomepizole-treated (hypotension, bradycardia) cases. Median adverse drug event onset was within 3 hours after the start of either antidote. Ethanol and fomepizole adverse drug event rates were 0.93 and 0.13 adverse drug events per treatment-day, respectively. Adjusted hazard ratio was 0.16 (95% confidence interval 0.06, 0.40). CONCLUSION: Given observational study limitations, results suggest lower occurrence of adverse drug events with fomepizole than ethanol.