Opioid Conversion Calculator

Cross-tolerance between opioids is incomplete. This means tolerance to one opioid doesn't fully transfer to another. A 25-50% reduction is recommended to prevent overdose. Start lower (50% reduction) for elderly, debilitated patients, or high doses; less reduction (25%) may be appropriate for severe pain or if prior opioid dose was inadequate.

Methadone is unique: (1) Its equianalgesic ratio changes based on the morphine dose being converted - higher morphine doses require proportionally less methadone. (2) It has a very long, variable half-life (8-59 hours) leading to accumulation. (3) It can prolong QTc interval. Always use methadone-specific conversion tables and consult pain/palliative care specialists.

Consider rotation when: (1) Pain is poorly controlled despite dose increases. (2) Intolerable side effects (nausea, constipation, sedation, cognitive impairment). (3) Concern for tolerance or hyperalgesia. (4) Need for different route. (5) Drug availability or cost issues. Rotation often restores analgesic efficacy due to incomplete cross-tolerance.

Conversion ratios are approximations with significant inter-patient variability (up to 2-3 fold). Factors affecting accuracy include: genetics (CYP450 polymorphisms), age, organ function, drug interactions, pain type, and prior opioid exposure. These calculations provide a starting point - individual titration based on response is essential.

OME standardizes opioid doses to equivalent oral morphine. This allows comparison across different opioids and routes. CDC uses OME thresholds for risk assessment: ≥50 mg/day increases overdose risk; ≥90 mg/day requires careful justification. OME helps ensure appropriate prescribing and identifies high-risk patients.