American College of Medical Toxicology and the American Academy of Clinical Toxicology position statement: nalmefene should not replace naloxone as the primary opioid antidote at this time

"As physicians, pharmacists, scientists, and specialists in poison information, we are experts in pharmacology, toxicology, and the management of opioid overdose and addiction. We applaud the effort to seek out new therapeutic strategies for the management of these patients.

"We are concerned that the use of a longer-acting reversal agent would not improve on current practice and could potentially cause harm. When withdrawal is precipitated by an opioid antagonist, there are few good management options. In most cases, the best strategy is to address and support the patient’s signs and symptoms until the effects of the antagonist wane. In the case of naloxone, which has a relatively short duration of action, severe withdrawal usually lasts less than an hour with symptoms typically persisting no more than 90 min [Citation25–27]. A longer-acting antagonist is anticipated to cause longer-lasting precipitated withdrawal and may lead to worse patient outcomes. Clinical experience with both naltrexone and nalmefene suggests prolonged withdrawal is a complication of longer-acting opioid antagonists [Citation28]. Although a longer-acting antagonist may be theoretically beneficial for the resuscitation of opioid-naive individuals in an opioid-induced mass casualty incident, this type of event has never been reported in North America and this application is unstudied.

"We are also concerned that patients who receive nalmefene may require longer periods of observation, by up to several hours, to observe for recrudescent effects as the antagonist effects wane. Patients who receive nalmefene will still need medical observation to ensure that respiratory depression does not recur after the effects of the medication subside. This will prolong emergency department visit length and challenge patient and clinician expectations, further burdening a taxed system. Further clinical study is needed to understand whether a reduction in repeat antagonist use justifies a longer length of stay or longer period of withdrawal.

"Finally, we are concerned that intranasal nalmefene has not been adequately studied for effectiveness in the actual setting and patient population: for patients with severe opioid intoxication in the out-of-hospital environment. Lack of proof of safety and efficacy in real-world use could result in significant harm if widely utilized.

"The potential benefits of nalmefene over naloxone (greater opioid receptor affinity, longer duration action) carry the risk of causing harm. These benefits, if present, should be demonstrated in the clinical environment, balanced with the risks, and compared to naloxone prior to the broad adoption of nalmefene."