Opioid Antagonists

Opioid Antagonists are drugs that block opioid receptors, reversing opioid effects and treating overdose or dependence.

Definition:

• Drugs that block opioid receptors, reversing the effects of opioids.
• They have high affinity but no intrinsic activity at opioid receptors.

Main Opioid Antagonists:

1. Naloxone

   • Pure opioid antagonist (high affinity for μ-receptors)
   • Rapid onset, short duration (1–2 hours)
   • Administered IV, IM, SC, or intranasally
   • Uses:
     • Acute opioid overdose
     • Reverses respiratory depression
     • Diagnostic test for opioid intoxication
   • Limitation:
     • May require repeated doses due to short action

2. Naltrexone

   • Oral opioid antagonist
   • Longer duration than naloxone
   • Uses:
     • Maintenance therapy in opioid and alcohol dependence
     • Prevents relapse by blocking euphoric effects of opioids
   • Not used in acute overdose (slow onset)

3. Nalmefene

   • Similar to naltrexone, long-acting
   • Used in alcohol dependence and opioid overdose

4. Methylnaltrexone / Alvimopan

   • Peripheral opioid antagonists
   • Do not cross the blood-brain barrier
   • Used to treat opioid-induced constipation without affecting analgesia

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