Onset of symptoms after methadone overdose

Abstract

Background: Methadone ingestion may cause delayed coma and require naloxone infusion. Few studies exist regarding the time development of symptoms following methadone overdose in adults.

Methods: After a brief training period, reviewers who were blinded to the purpose of the study completed a standardized data collection sheet. Two consecutive years of poison center patient encounters were reviewed. Age, outcomes, coingestions, vital signs, clinical manifestations, hospital admissions, and mortality were abstracted. Data were analyzed using descriptive statistics. The first reviewer was designated to extract the data. The second reviewer conducted a review of 20% of all the charts for a kappa value to be calculated.

Results: In total, 44 cases of isolated methadone overdose in patients older than 18 years were identified. A mean age of 32.5 (18-58) years and a mean presumed ingestion of 106 mg of methadone was calculated. Of the 44 patients, 32 received naloxone for symptoms consistent with opiate toxicity. All symptoms occurred within 9 hours of methadone ingestion, with a mean symptom onset of 3.2 hours. All patients had resolution of symptoms within 24 hours. No deaths were recorded. The kappa score for interreviewer reliability was 0.69, with a 95% confidence interval of 0.58 to 0.73.

Limitations: This was a retrospective study that was limited by patient history.

Conclusion: Acute methadone toxicity typically results in symptoms within 9 hours of ingestion.