Amitriptyline
Class: Tricyclic antidepressant
Indications: Depression, neuropathic pain, migraine prophylaxis
Contraindications/cautions: Recent MI or heart block; urinary retention without urinary catheter insitu; angle-closure glaucoma. Caution in epilepsy; bipolar disorder, suicidal ideation.
Adverse reactions: common: Constipation, dry mouth, blurred vision, sedation (increased in hepatic impairment); less common: photophobia, urinary retention, tachycardia, confusion, delirium, postural hypotension, sweating, QT-prolongation.
Metabolism/clearance: metabolised to nortriptyline by CYP2C19 and CYP2C8/9 in the liver. Negligible renal clearance.
Interactions: serotonin syndrome with other serotonergic drugs (caution); QT-prolonging drugs, MAOI’s (contraindicated)
| Dosing: | |
|---|---|
| oral: | neuropathic pain: 10 mg at night – increase gradually to 25 to 50 mg at night. Maximum 75 mg but rarely tolerated in palliative patients |
| subcut: | N/A |
| rectal: | N/A |
Syringe driver: N/A
Mechanism of action: analgesic effects may be through noradrenaline & serotonin pathways – also opioid agonism, alpha adrenoreceptor blockade and ion channel blockade to reduce transmission.
Half life: 15 hours (metabolite nortriptyline half life of 30 hours)
Onset: oral: can take a few weeks or up to 6 weeks for full effect vs pain
Notes: lower doses used for pain; higher doses used in depression. Tablets may be film coated – can be halved and likely to be able to be crushed
Availability:
- tablets 10 mg, 25 mg, 50 mg