Opioid Reversal

Opioid Antagonists

Naloxone (Narcan)

Pure antagonist of μ, κ, and δ receptors. Must be administered with caution – if too aggressive, can elicit extreme pain, HTN, arrhythmias, pulmonary edema, and death (thought to be due to massive catecholamine response to pain), as well as opioid withdrawal symptoms in patients who require opioids. Peak effect within 1-2 minutes may last up to 4 hours (but duration is variable). Small doses of 20-40 μcg are prudent. Infusion rate is 3-10 μcg/hr

Naltrexone

Long acting oral opioid antagonist, also a pure antagonist

Mixed Agonists-Antagonists

Nalbuphine

μ-antagonist, κ-agonist (possible δ activity). Minimal MAC reduction in animal studies (~ 8%) thus not particularly useful during general anesthesia. Main purported advantage is ceiling effect of respiratory depression (μ2-mediated), thought to be approximately equal to 0.4 mg/kg morphine. Reduces itching after intrathecal opioid administration.Antagonist/partial agonist of μ receptors, κ-agonist. Like nalbuphine, also exhibits minimal MAC reduction in animal studies (~ 11%), but unlike nalbuphine, is more sedating

Buprenorphine

Partial agonist of μ receptors, possible antagonist at κ receptor.

Opioid Reversal

• Naloxone: pure μ, κ, and δ antagonist. 20-40 μcg IV, onset 1-2 mins. May cause extreme pain, HTN, arrhythmias, pulmonary edema, and death
• Naltrexone: pure antagonist, oral equivalent of naloxone
• Nalbuphine: μ-antagonist, κ-agonist (possible δ activity). Reduces itching after intrathecal opioid administration
• Butorphanol: antagonist/partial agonist of μ receptors, κ-agonist
• Buprenorphine: partial agonist of μ receptors, no or antagonist at κ receptors. Shows resistance to reversal from naloxone.