Venlafaxine
Class: antidepressant โ SNRI โ serotonin and noradrenaline reuptake inhibitor
Indications (NB some may be unlicensed): depression, anxiety & panic disorders, neuropathic pain, hot flushes
Contraindications/cautions: renal/hepatic failure, volume depletion, epilepsy, mania, heart disease; risk of QT prolongation
Adverse reactions: common: nervousness, headache, fatigue, blood pressure changes, dizziness, dry mouth, insomnia, drowsiness, weight gain or loss, GI effects, nausea, constipation, sexual dysfunction, sweating, weakness, prolongation of the QT interval less common: tremor, mania, anxiety, palpitations, heart failure, loss of consciousness, seizures, blood disorders, hepatitis, arrhythmias, neuroleptic malignant syndrome, pancreatitis, extrapyramidal adverse effects, hypercholesteraemia
Metabolism/clearance: metabolised by metabolising enzyme CYP2D6 mainly in the liver to active metabolites. Some venlafaxine and some of its metabolites are excreted by the kidneys
Interactions:
- increased clinical effect/toxicity of venlafaxine (due to increased blood concentrations) may occur with some CYP metabolising enzyme inhibitors (see above) e.g. bupropion, fluoxetine, paroxetine, quinine
- increased clinical effect/toxicity of some drugs (due to increased blood concentrations of them) may occur with venlafaxine due to metabolising enzyme inhibition e.g. codeine (effect may be decreased due to lack of metabolism to morphine), nortriptyline
- increased risk of serotonin syndrome with MAOIs e.g. phenelzine so avoid venlafaxine within 2 weeks of MAOI therapy
- increased risk of prolonged QT interval with other drugs that prolong the interval e.g. haloperidol
- dose of warfarin may need to be reduced when given concurrently with venlafaxine
| Dosing: | ||
|---|---|---|
| oral: | slow release | Elderly โ start on 37.5 mg od; others start on 75 mg od; increase by 75 mg once daily every 2 weeks โ maximum 375 mg od |
| subcut: | not available | |
| rectal: | not available |
Syringe driver: not available
Mechanism of action: inhibits reuptake of serotonin (at high dose), noradrenaline and dopamine in the CNS
Notes:
- take with or after food to improve tolerability
- in severe renal or mild-moderate hepatic impairment, reduce dose by 50% and give once daily
- monitor bp at commencement and dose increases
- neuropathic pain โ 37.5 to 75 mg od โ can increase gradually to max 375 mg od
- hot flushes โ 37.5 mg od โ can increase to 75 mg od if necessary