What does MME (Morphine Milligram Equivalents) mean in the context of opioid therapy for pain management?

What is MME (Morphine Milligram Equivalents)?

MME (Morphine Milligram Equivalents) is a standardized metric that converts different opioid medications and doses into an equivalent amount of morphine, allowing clinicians to calculate total opioid burden for risk assessment and monitoring cumulative exposure across multiple prescriptions. 1

Purpose and Clinical Application

MME serves as a universal measurement tool to:

• Assess overdose risk by calculating total daily opioid exposure, with critical thresholds at ≥50 MME/day and ≥90 MME/day 2
• Monitor cumulative opioid burden across multiple prescriptions and different opioid formulations 2
• Identify high-risk patients who may require closer monitoring or intervention 2

The CDC established these conversion factors primarily for risk stratification rather than for direct dose calculations when switching between opioids. 2

How to Calculate MME

To determine MME, multiply the total daily dose of each opioid by its specific conversion factor. 1

Standard Conversion Factors (CDC Guidelines):

• Morphine: 1.0 1, 3
• Codeine: 0.15 1
• Hydrocodone: 1.0 1, 4
• Oxycodone: 1.5 1, 2, 3
• Hydromorphone: 4.0 (oral); additional potency consideration for IV 1, 3
• Oxymorphone: 3.0 1
• Fentanyl transdermal: 2.4 (per μg/h) 1
• Tapentadol: 0.4 1
• Methadone: Variable (4.0 for 1-20 mg/day; 8.0 for 21-40 mg/day; 10.0 for 41-60 mg/day; 12.0 for ≥61-80 mg/day) 1

Practical Example:

Hydrocodone 5 mg tablets taken 4 times daily:

• Total daily dose: 20 mg
• Conversion factor: 1.0
• MME = 20 mg × 1.0 = 20 MME/day 1

Oxycodone ER 10 mg tablets taken twice daily:

• Total daily dose: 20 mg
• Conversion factor: 1.5
• MME = 20 mg × 1.5 = 30 MME/day 1, 2

Critical Safety Thresholds

Doses ≥50 MME/day warrant careful reassessment of individual benefits and risks before any further dosage increases. 2

Doses ≥90 MME/day are associated with progressively increased overdose risk and require the CDC's most intensive monitoring. 2, 3

The Most Dangerous Pitfall: Bidirectional Use

Never use MME calculations in reverse to determine a new opioid dose when switching medications—this is the most common and dangerous error. 2

The conversion factors tell you how much morphine equivalence you're prescribing for risk assessment purposes only. 2 When actually rotating between opioids:

• Always reduce the calculated equianalgesic dose by 25-50% due to incomplete cross-tolerance 2, 4
• The conversion factors are estimates only and cannot account for individual variability in genetics and pharmacokinetics 2
• Using MME bidirectionally can lead to accidental overdose 2

Special Considerations

Route of administration significantly affects potency: IV opioids are 2-3 times more potent than oral equivalents due to avoidance of first-pass metabolism. 3 This must be factored into MME calculations for parenteral opioids.

Tapentadol has unique pharmacology: As both a μ-receptor agonist and norepinephrine reuptake inhibitor, its MME is based on μ-receptor activity alone, but it's unknown if overdose risk follows the same dose-dependent pattern as pure μ-agonists. 1

Individual patient factors including pharmacokinetics, tolerance, renal function, and hepatic function can significantly affect clinical response despite identical MME values. 2, 4, 3