Long-acting synthetic opioid
Methadone hydrochloride
Brand names: Physeptone
Adult dose
Dose: Opioid substitution: initial 10–20mg PO OD, titrate weekly (max 30mg/day in week 1). Maintenance 60–120mg OD. Pain: complex — specialist palliative input
Route: PO/SC
Frequency: OD
Clinical pearls
- Long half-life (15–60h) — 5–7 days to steady state; risk of accumulation toxicity
- Baseline ECG; repeat at week 2 and after dose >100mg/day
- Take-home doses per local opioid-substitution policy
Contraindications
- Acute respiratory depression
- Concurrent QT-prolonging drugs (caution)
- Concurrent MAOI/within 14 days
- Risk of paralytic ileus
- Phaeochromocytoma
- Acute alcohol intoxication
Side effects
- Respiratory depression
- Sedation
- Constipation
- QT prolongation / torsades (especially >100mg/day)
- Hypogonadism
- Dependence
Interactions
- Many — strong CYP3A4 inducers (rifampicin, efavirenz) reduce levels; CYP3A4 inhibitors raise
- QT-prolonging drugs
- CNS depressants
- Carbamazepine
Monitoring
- ECG
- Mental state
- Sedation
- Drug screen (during induction)
Reference: BNF; NICE CG52; PHE/UK clinical guidelines on drug misuse; https://bnf.nice.org.uk/drugs/methadone-hydrochloride/. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Calculators
- Morphine Milligram Equivalents (MME) Calculator · Pain / Opioids
- Opioid Conversion / Equianalgesic Guide · Pain Management
- Corrected QT Interval (Bazett) · ECG
- Bazett Corrected QT Interval (QTc) Calculator · Arrhythmia
- Long QT Syndrome (Schwartz Score) · Channelopathy / Sudden Cardiac Death
- Numeric Rating Scale (NRS) Pain Assessment and Management · Pain Management
Pathways
Same specialty