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

Abstract

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.

Keywords:

• Fomepizole
• Ethanol
• Medication error
• Antidotes
• Toxic alcohol poisoning

Acknowledgements

We acknowledge with thanks the advisory panel who assisted with development of medication error definitions: Caroline Bailey MSc RPh, Kyla Bertschi, BSc.(Pharm), Glen Brown Pham.D, Gerald Da Roza MD, Marlyce Friesen MD, Devin Harris MD, Garth Hunte MD, Debra Kent Pharm.D, Bruce Lange Pharm.D, Christopher Lo Pharm.D, David MacDonald BTSN, Fruzsina Pataky BSc(Pharm), Suzanne Tytler BSN, J.R. Wesgtate BSN, Peter Zed Pharm. D. We gratefully acknowledge the support of staff at the BC Drug and Poison Information Centre and participating hospitals. KJL was supported by a training fellowship from the Michael Smith Foundation for Health Research (MSFHR). ARL was supported by MSFHR senior scholar and Canadian Institutes of Health Research new investigator awards. BGS was supported by the Canada Research Chair Program.

Appendix. Study definitions

Table A1. Treatment recommendations (available in 1996–2005) for use of ethanol and fomepizole as antidotes for methanol or ethylene glycol poisoning.*

Table A2. Ethanol and fomepizole medication error definitions and thresholds.