Opioid Conversion / Equianalgesic Guide
Guides conversion between opioid analgesics using oral morphine equivalents (OME). Start at 50–75% of calculated equianalgesic dose due to incomplete cross-tolerance.
Score interpretation
Low-dose opioid, normal organ function. Standard conversion ratios apply.
→ Conversion ratios (approximate): Oral morphine = reference (1:1). IV/SC morphine = oral ÷ 3. Oral oxycodone = oral morphine ÷ 1.5. Oral codeine = oral morphine ÷ 10. Oral tramadol = oral morphine ÷ 5. Fentanyl patch (mcg/h) = daily oral morphine ÷ 2.4. Prescribe laxatives (senna + lactulose). PRN dose = 1/6 of total daily dose.
Moderate renal impairment or moderate-high opioid dose. Risk of over-sedation.
→ Start at 50–75% of calculated equianalgesic dose. Titrate upward by 25–33% every 24–48h as tolerated. In renal impairment (eGFR 10–50): prefer oxycodone or hydromorphone. Monitor sedation (RASS), respiratory rate, pain scores. Palliative care or pain team review if uncertain.
Severe renal failure or high-dose conversion: HIGH RISK of respiratory depression.
→ AVOID morphine if eGFR < 10 — M6G accumulation causes respiratory depression. Use fentanyl or alfentanil (hepatically metabolised, renally excreted as inactive). Start at 33% of equianalgesic dose. Naloxone 400 mcg diluted to 10 mL, 1–2 mL IV every 2 min to effect. Mandatory palliative care / pain specialist review.
Interpretation bands for the Opioid Conversion. Apply clinical judgement and local guidance.
References
- Faculty of Pain Medicine (RCOA). Opioid Aware: A resource for patients and healthcare professionals to support prescribing of opioid medicines for pain. 2020.
- NICE NG215. Chronic pain (primary and secondary) in over 16s. 2021.
Related
Curated clinical cross-links plus same-class fallbacks.
- Fentanyl Transdermal Patch (Elderly Chronic Pain) · Opioid Analgesic — Transdermal Patch
- Morphine Slow-Release (Elderly Chronic Pain) · Opioid Analgesic — Modified-Release Oral
- Morphine (Orthopaedic Acute Pain) · Opioid Analgesic — Strong
- Oxycodone (Orthopaedic Post-operative Pain) · Opioid Analgesic — Strong
- Morphine (Paediatric) · Opioid Analgesic — Moderate to Severe Pain in Children
- Fentanyl Patch (Burns Pain) · Opioid Analgesic (Transdermal)
- Difficult Airway Algorithm (DAS) · DAS 2015; Royal College of Anaesthetists
- Anaphylaxis Under Anaesthesia · AAGBI 2018; NAP6
- Malignant Hyperthermia · AAGBI 2011; MHAUS
- Local Anaesthetic Systemic Toxicity (LAST) · AAGBI 2010; ASRA 2017
- Spinal Anaesthesia Hypotension Management · AAGBI; ASA
- Postoperative Nausea & Vomiting · Society for Ambulatory Anesthesia 2020; AAGBI
Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.