The European Medicines Agency (EMA) has recommended strengthening existing advice to minimize the risks from interactions between Mysimba (naltrexone/bupropion; Orexigen Therapeutics Ireland Limited) and opioid-containing medicines. The recommendation followed a routine review of the safety of the weight loss medication.
The EMA's Committee for Medicinal Products for Human Use (CHMP) advised that opioid painkillers may not work effectively in patients taking Mysimba because one of the active substances in the treatment, naltrexone, blocks the effects of opioids.
Advice for Patients and Healthcare Professionals
The EMA advised that patients should stop taking Mysimba for at least 3 days before beginning treatment with opioid medications such as morphine and codeine; other opioids used during surgery; and certain medicines for cough, cold, or diarrhea. It is said there is a rare but serious and potentially life-threatening risk for reactions, such as seizures and serotonin syndrome, if the drugs are taken together.
The new recommendation is in addition to existing contraindications, which state that Mysimba must not be used in people who are dependent on long-term opioids, people receiving treatment with opioid agonists such as methadone, and people going through opioid withdrawal.
The EMA highlighted that a test should be performed to ensure clearance of opioid medication before starting treatment with Mysimba.
Appetite Reduction and Increased Energy Expenditure
Mysimba was granted marketing authorization in March 2015. Exactly how the treatment works is not fully understood. The combined actions of its two component drugs, naltrexone and bupropion, reduce appetite and the amount that patients eat and increase energy expenditure, helping patients maintain a calorie-controlled diet and reduce their body weight.
The treatment is used alongside diet and exercise to help manage weight in adults who have obesity (body mass index [BMI], 30 or more) or overweight (BMI, 27-30) and who have weight-related complications such as diabetes or hypertension.
The effects of Mysimba on reducing body weight had been demonstrated in four main studies, in which Mysimba was compared with placebo, explained the CHMP.
In three of the studies, the average weight loss was around 3.7%-5.7% in patients treated with Mysimba compared with 1.3%-1.9% in those treated with placebo. In the fourth study, in which patient counselling was more intensive, the overall weight loss was 8.1% with Mysimba and 4.9% with placebo.
Mysimba is available as prolonged-release tablets containing 7.2 mg naltrexone and 78 mg bupropion. Treatment is commenced with a single tablet each morning, with the dose gradually increased over 4 weeks to the recommended dose of two tablets twice daily, preferably taken with food.
Patients should have their response and tolerability to the medicine checked regularly, and treatment should be stopped in patients who have certain side effects, such as an increase in blood pressure. Mysimba should also be stopped if patients have not lost at least 5% of their initial body weight after 4 months of treatment.