Meperidine Potency Compared to Morphine
Meperidine is approximately one-tenth as potent as morphine, meaning 60-80 mg of parenteral meperidine is roughly equivalent to 10 mg of parenteral morphine. 1
Equianalgesic Dosing
The FDA-approved drug label for meperidine clearly establishes the potency relationship:
- 60-80 mg of parenteral meperidine = 10 mg of parenteral morphine 1
- This translates to a potency ratio of approximately 6:1 to 8:1 (meperidine:morphine) 1
- Alternatively stated, meperidine has roughly one-tenth the analgesic potency of morphine 2
Route-Specific Considerations
Oral administration of meperidine is significantly less effective than parenteral routes, though the exact oral-to-parenteral ratio remains unknown. 1 This poor oral bioavailability makes meperidine unsuitable for routine oral pain management. 3
For parenteral morphine conversions:
- The onset of action with meperidine is slightly more rapid than morphine 1
- Duration of action is slightly shorter (typically 3-4 hours) 3
- Peak effects occur within 15-30 minutes with parenteral administration 3
Clinical Guidelines Context
NCCN guidelines describe tramadol as approximately one-tenth as potent as morphine 4, which places meperidine in a similar potency range. However, unlike tramadol, meperidine is a traditional mu-opioid receptor agonist without the dual mechanism of action. 4
Morphine remains the opioid of first choice for moderate to severe cancer pain 4, with meperidine generally considered a second-line agent due to its neurotoxic metabolite normeperidine. 3
Important Clinical Caveats
- Meperidine should be considered a second-line agent when opioid analgesics are required 3
- The active metabolite normeperidine has potent CNS excitatory toxicity, with half-life significantly prolonged in renal insufficiency 4
- Meperidine is contraindicated with monoamine oxidase inhibitors (MAOIs) due to life-threatening drug interactions 4
- Despite the established potency ratio, meperidine continues to be inappropriately prescribed, particularly for shorter courses of narcotic therapy 5