Analgesia
build the regimen
| step | agents |
|---|---|
| 1 · base, regular | Paracetamol ± NSAID |
| 2 · weak opioid | Tramadol |
| 3 · strong opioid | Morphine, oxycodone |
- add an adjuvant at any step for neuropathic pain
starting doses
| drug | dose | caution |
|---|---|---|
| Paracetamol | 1 g QDS (max 4 g/day) | reduce if < 50 kg, frail, or liver disease |
| Ibuprofen | 400 mg TDS (max 2.4 g/day) | avoid in AKI, GI bleed risk, cardiac, elderly |
| Ketorolac | 10–30 mg IV/IM (max 90 mg/day; 60 mg if elderly or < 50 kg; max 5 days) | NSAID cautions; short-term only |
| Tramadol | 50–100 mg QDS | serotonergic, lowers seizure threshold, caution in elderly |
| Morphine (oral IR) | 5–10 mg PRN (2.5–5 mg if frail / renal) | see renal note |
| Morphine (IV) | titrate 1–2 mg increments | monitor sedation + RR |
opioid conversion
approximate: verify against local / palliative guidance
| from → to | factor |
|---|---|
| Tramadol → oral morphine | ÷ 10 (approx) |
| oral morphine → oral oxycodone | ÷ 1.5–2 |
| oral morphine → SC morphine | ÷ 2 |
| oral morphine → SC diamorphine | ÷ 3 |
- breakthrough dose = 1/6 of the total 24-hour opioid dose
renal impairment
- avoid morphine: active metabolites accumulate (sedation, respiratory depression)
- prefer oxycodone (with caution) or, in specialist hands, alfentanil
- reduce all doses and lengthen intervals
always co-prescribe with a strong opioid
- a laxative: opioids constipate predictably
- a PRN antiemetic
- naloxone available for toxicity:
- ward opioid toxicity / opioid-dependent: 100 mcg (0.1 mg) IV, repeat every 2–3 min, titrate to respiratory rate > 12 (not to full alertness)
- severe respiratory depression / peri-arrest: 400 mcg (0.4 mg) IV/IM, repeat every 2–3 min; no IV/IM access: 2 mg intranasal
- recurrent depression → infusion at approximately two-thirds of the effective bolus dose per hour
neuropathic pain
- amitriptyline, gabapentin / pregabalin, or duloxetine: first-line over opioids
opioid safety
naloxone wears off before the opioid does
- titrate in small increments to breathing, not to full reversal (dose per local protocol)
- respiratory depression recurs as naloxone washes out: keep monitoring well beyond the dose, longer after modified-release opioids, methadone or a patch
- repeat doses needed → infusion + higher-level monitoring, escalate
- renal impairment: morphine and codeine accumulate (M6G). Avoid below a creatinine clearance of about 30 mL/min; fentanyl or alfentanil are safer, oxycodone with reduction and monitoring
- gabapentinoids with opioids: serious respiratory depression. Highest risk if age ≥ 65, COPD, renal impairment, or concurrent benzodiazepines
- combination tablets: count the paracetamol they contain toward the daily maximum
red flags
opioid toxicity
- falling respiratory rate or rising sedation score → hold the opioid, reassess, naloxone if toxic
Verify indication, dose, allergies, interactions, renal/hepatic function and local protocols before prescribing.
studying for the IM exam? the IM Rapid Review covers analgesia and opioid conversion in the same format. see the sample chapter.
Last clinically reviewed · June 2026 · Last updated · August 2026