Dosing protocol and analgesic efficacy determine opioid tolerance in the mouse

Area of Science:

• Pharmacology
• Pain Management

Background:

• Opioid analgesic efficacy and dosing protocols influence analgesic tolerance.
• Understanding opioid tolerance is crucial for effective pain management.

Purpose of the Study:

• To investigate the relationship between opioid analgesic efficacy and tolerance.
• To compare tolerance development from acute, intermittent, and continuous opioid administration.
• To test if higher analgesic efficacy correlates with less tolerance.

Main Methods:

• Determined analgesic efficacy (tau) of etorphine, methadone, oxycodone, and hydrocodone using the operational model of agonism.
• Induced tolerance in mice via acute, intermittent (once daily for 7 days), or continuous infusion (7 days) of opioid agonists.
• Conducted morphine dose-response studies post-treatment to assess tolerance.

Main Results:

• Analgesic efficacy order: etorphine > methadone > oxycodone ≈ hydrocodone.
• Continuous infusion of higher efficacy etorphine resulted in less tolerance than lower efficacy opioids at equi-effective doses.
• Intermittent and acute administration produced less tolerance than continuous infusion.

Conclusions:

• Intermittent and acute opioid administration lead to minimal tolerance compared to continuous infusion.
• Continuous infusion shows an inverse relationship between analgesic efficacy and tolerance.
• Clinical use of sustained-release formulations or continuous infusions may increase opioid analgesic tolerance.