Etorphine inhibition of pancreatic exocrine secretion in rats: comparison with methadone

Methadone Use and the Risk of Hypoglycemia for Inpatients With Cancer Pain

CONTEXT

Methadone is an important drug in the management of both cancer-related and non-cancer-related pain and is the main pharmacologic agent used in the treatment of opioid addiction. Unexpected hypoglycemia has been observed in patients receiving methadone, prompting a more detailed investigation.

OBJECTIVES

To evaluate the incidence of hypoglycemia in a cohort of inpatients receiving methadone versus other opioids including fentanyl, hydromorphone, and morphine.

METHODS

Retrospective observational cohort of inpatients in a tertiary cancer center admitted for more than 48 hours from November 1, 2011 to October 30, 2013. The main outcomes were lowest measured daily blood glucose (in mg/dL) and incidence of hypoglycemia (defined as blood glucose < 70 mg/dL, equivalent to 3.9 mmol/L) with variable methadone doses compared with other non-methadone opioids.

RESULTS

Of the 641 eligible patients admitted during the study period who received at least one dose of methadone during admission, multivariable logistic regression showed significant associations between methadone and hypoglycemia at doses greater than 40 mg oral equivalents per day or with patient-controlled analgesia use. A dose-response relationship was observed, with an odds ratio of 3.1 (95% confidence interval 2.5, 3.6) when doses greater than 80 mg/day were used. No evidence of increased risk of hypoglycemia or of a dose-response curve was seen for the other opioids.

CONCLUSION

The risk of hypoglycemia is increased for patients taking more than 40 mg oral methadone equivalents per day. When starting methadone at or more than 40 mg/day, we recommend blood glucose monitoring.

Severe hypoglycemia during methadone escalation in an 8-year-old child

This case report describes hypoglycemia during methadone escalation in an 8-year-old girl with acute lymphatic leukemia. After a significant increase in the methadone dosage, the blood glucose decreased from 12 mmol/l to 1 mmol/l. Nutrition and other medications were meticulously checked and no other apparent explanation was found. There are few reports from the adult palliative setting which describe this serious side effect. This is to our knowledge, the first described pediatric case.

Methadone-induced hypoglycemia

To determine if recent observations of hypoglycemia in patients receiving high-dose methadone extended to an animal model, we explored the effects of methadone and other mu-opioids on blood glucose levels in mice. Methadone lowered blood glucose in a dose-dependent manner with 20 mg/kg yielding a nadir in average glucose levels to 55 ± 6 mg/dL from a baseline of 172 ± 7 mg/dL, an effect that was antagonized by naloxone and mu selective antagonists β-funaltrexamine and naloxonazine. The effect was stereoselective and limited to only the l-isomer, while the d-isomer was ineffective. Despite the robust decrease in blood glucose produced by methadone, a series of other mu-opioids, including morphine, fentanyl, levorphanol, oxycodone or morphine-6β-glucuronide failed to lower blood glucose levels. Similar differences among mu-opioid agonists have been observed in other systems, suggesting the possible role of selected splice variants of the mu-opioid receptor gene Oprm1. This mouse model recapitulates our clinical observations and emphasizes the need to carefully monitor glucose levels when using high methadone doses, particularly intravenously, and the need for controlled clinical trials.

Modulation by alcohol and methadone of 2-deoxyglucose-stimulated pancreatic secretion in the rat

Alcohol intake is a major problem in drug addicts, and it is not clear whether the effects of alcohol and opiates are additive or potentiating. Vagally stimulated pancreatic secretion in rats is potently inhibited by opiates acting centrally at mu-receptors. In the present experiments, we determined the effects of methadone on 2-deoxyglucose (2DG)-stimulated pancreatic secretion in rats treated with acute (1.9 g/kg.3 h, intravenously) or chronic (1 or 3 month drinking) ethanol. In both acute and 1 month chronic alcoholic rats, methadone administered at its 50% inhibitory dose (ID50) reduced by about 50% 2DG-stimulated pancreatic secretion of sodium, bicarbonate and protein, and ethanol had only faint, nonsignificant inhibitory effects. In 3 month chronic alcoholic rats, similar results were obtained, but methadone inhibited 2DG-stimulated pancreatic secretion by 60 to 90% in these older rats. No significant interaction was found in any condition between ethanol and methadone, suggesting that they had only additive, but not potentiating effects in this method.