Fluoxetine

Class: antidepressant – SSRI (Selective Serotonin Re-uptake Inhibitor) – increases serotonin in the brain

Indications (NB some may be unlicensed): depression and associated anxiety, bulimia nervosa, obsessive-compulsive disorder, premenstrual dysphoric disorder, neuropathic pain

Contraindications/cautions: epilepsy, bleeding disorders (decreases platelet aggregation); use of MAOI within 14 days; QT prolongation; serotonin syndrome (oxycodone; fentanyl)

Adverse reactions: common: nausea, sweating, tremor, diarrhoea (excessive serotonin), taste disturbance, sexual dysfunction; less common: dry mouth, cough, constipation, postural hypotension, tachycardia, somnolence, amnesia, visual disturbances, pruritus, hyponatraemia

Metabolism/clearance: metabolised by metabolising enzyme CYP2D6 mainly in the liver

Interactions:

• increased clinical effect/toxicity of fluoxetine (due to increased blood concentrations) may occur with some CYP metabolising enzyme inhibitors (see above) e.g. bupropion, paroxetine (not citalopram), quinine
• increased clinical effect/toxicity of some drugs (due to increased blood concentrations of them) may occur with fluoxetine due to metabolising enzyme inhibition by fluoxetine e.g. amitriptyline, codeine (decreased morphine concentrations so decreased clinical efficacy of codeine), haloperidol, metoclopramide, nortriptyline, promethazine, tamoxifen (decreased endoxifen (active metabolite) concentrations so decreased clinical effects)
• additive risk of serotonin syndrome (potentially fatal syndrome – symptoms include sweating, diarrhoea, confusion) with other serotonergic drugs e.g. carbamazepine, citalopram, tricyclic antidepressants (e.g. amitriptyline), lithium, tramadol, some opioids

Syringe driver: not available

Mechanism of action: blocks the reuptake of serotonin, a neurotransmitter, in the CNS

Onset: depression/anxiety: 2 to 4 weeks pain: 3 to 7 days

Peak response: 5 to 6 weeks

Notes:

• fluoxetine has a half life of 48 hours but its active metabolite (norfluoxetine) has a half life of 11 days
• reduce dose or increase dose interval in hepatic impairment
• watch for serotonin syndrome if switching antidepressants as it takes 4 to 5 half lives to clear a drug from the body i.e. 44 to 55 days for fluoxetine/norfluoxetine
• withdrawal symptoms on stopping fluoxetine are unlikely to occur
• tablets are dispersible in water allowing dosing increments of < 20 mg. Capsule contents are also dispersible in water