Lomotil (Diphenoxylate) Has No Established MME Conversion Factor
Lomotil (diphenoxylate with atropine) is not included in standard morphine milligram equivalent (MME) conversion tables and should not be counted toward a patient's total daily MME burden. 1, 2
Why Diphenoxylate Is Excluded from MME Calculations
Diphenoxylate is a peripherally-acting opioid antidiarrheal agent, not an analgesic opioid, and the CDC's MME conversion framework was developed specifically for opioids prescribed for pain management and overdose risk assessment. 2
The standard MME conversion tables published by the CDC in 2016 and updated in 2022 do not list diphenoxylate among the opioids with established conversion factors (which include morphine, oxycodone, hydrocodone, hydromorphone, fentanyl, codeine, methadone, tramadol, and tapentadol). 1, 2
Diphenoxylate is formulated with atropine specifically to discourage abuse and is prescribed at doses far below those that would produce central opioid effects or contribute meaningfully to overdose risk. 3
Clinical Context
Lomotil is generally less effective than loperamide for acute diarrhea and requires a prescription, whereas loperamide does not. 3
The primary clinical concern with diphenoxylate relates to its antidiarrheal effects (potential for ileus or worsening of infectious dysentery), not its contribution to systemic opioid burden or respiratory depression risk. 3
When assessing a patient's total opioid exposure for safety monitoring (particularly at the 50 MME/day and 90 MME/day thresholds that trigger enhanced precautions), diphenoxylate should be excluded from the calculation. 2
Important Caveat
- If a clinician suspects a patient is misusing diphenoxylate for central opioid effects (taking supratherapeutic doses), this represents a substance use disorder concern that requires clinical intervention, but still does not warrant inclusion in routine MME calculations for prescribing safety thresholds. 2