Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
Efexor (Wyeth Australia)
37.5 mg, 50 mg and 75 mg tablets
Venlafaxine is an antidepressant structurally and chemically unrelated to all other antidepressant medications. It is thought to potentiate neurotransmitter activity by inhibiting the reuptake of serotonin and noradrenaline. Depressed patients taking venlafaxine are more likely to improve than those taking placebo. Venlafaxine appears to be of comparable efficacy to the tricyclic antidepressants.
After absorption, venlafaxine undergoes extensive first-pass metabolism which produces an active metabolite. The small amount of unchanged drug and the liver metabolites are mainly excreted in the urine. The half life is considerably shorter than most of the other currently available antidepressants, being 5 hours for the parent compound and 11 hours for the metabolite. Clearance can be reduced by hepatic or renal dysfunction. For most patients, the minimum effective dose is 75 mg a day given in divided doses with food.
During short term studies, approximately 28% of patients discontinued treatment a similar rate to other antidepressants. Adverse effects which were more frequent with venlafaxine than placebo included nausea, somnolence, dizziness, dry mouth and sweating. As animal studies suggest that venlafaxine has no affinity for muscarinic receptors, it may cause fewer anticholinergic adverse effects than other antidepressants.
There is little information about interactions between venlafaxine and other drugs. It is recommended that venlafaxine should not be given less than 14 days after ceasing treatment with a monoamine oxidase inhibitor.
There are limited data about the long term use of venlafaxine. When ceasing treatment, venlafaxine should be gradually withdrawn over 7 days if it has been taken for more than 6 weeks.