Opioid antagonists

[SH4:p120-121]

Class

Pure MOP receptor antagonists with no agonist activity

• Naloxone
• Naltrexone
• Nalmefene

High affinity for MOP receptors is characteristic

Structure

• Changes in the structure of an opioid agonist can convert the drug into an antagonist
• Most common change is substitution of an alkyl group for a methyl group on an opioid agonist
  * e.g. naloxone is the N-alkyl derivative of oxymorphone

Trivia

Old antagonists also had some agonist activities
* e.g. nalorphine, levorphanol
* Now been replaced