Which of the following is true of nalmefene?
It is approved to be sold as an over-the-counter drug.
It requires multiple doses.
It has a longer duration of action and remains in the body longer than naloxone.
It is available as an injectable only.
The correct answer and explanation is:
Correct Answer:
It has a longer duration of action and remains in the body longer than naloxone.
Explanation:
Nalmefene is an opioid antagonist that is structurally related to naloxone and is primarily used to reverse opioid overdoses. Similar to naloxone, nalmefene works by competitively binding to opioid receptors (mu, kappa, and delta) in the central nervous system, thereby displacing opioids and reversing their effects.
The distinguishing characteristic of nalmefene is its longer duration of action compared to naloxone. This prolonged effect can be advantageous in managing opioid overdoses, especially those involving long-acting opioids like methadone or extended-release formulations of fentanyl. Nalmefene’s half-life is approximately 8-10 hours, which is significantly longer than naloxone’s half-life of about 1-2 hours. Consequently, nalmefene provides a more sustained reversal of opioid effects, reducing the need for multiple doses and potentially preventing the reemergence of respiratory depression once naloxone wears off.
Clarifications on Other Options:
- Over-the-Counter Availability: Nalmefene is not approved as an over-the-counter drug. It requires a prescription and is generally administered by healthcare professionals in clinical settings.
- Multiple Doses: Unlike naloxone, which often requires repeated dosing due to its short half-life, nalmefene typically does not require multiple doses because it remains active in the body for a longer period.
- Formulation: Nalmefene is available in both injectable and oral forms. The injectable form is commonly used for acute opioid overdose management, while oral formulations have been explored for alcohol dependence treatment.
Nalmefene’s extended duration of action and broader receptor activity make it a useful alternative to naloxone in specific cases. However, its slower onset of action compared to naloxone may limit its use in emergency situations where immediate opioid reversal is critical.