Venlafaxine

Venlafaxine is an antidepressant classed as a serotonin and noradrenaline reuptake inhibitor (SNRI). It increases the activity of two chemical messengers involved in mood, which is why it is sometimes chosen when other antidepressants have not helped enough. According to the UK SmPC for the standard tablets, it is used in adults to treat episodes of major depression and to reduce the risk of further episodes once the current one has eased. It is not recommended for anyone under 18, because clinical trials in young people did not establish that it works.

The 37.5 mg strength is listed in packs of 30, 60, 90, 120, 180, 240 or 360 tablets, and the 75 mg strength in packs of 10, 30, 60, 90, 120, 180, 240 or 360 tablets. These are imported generic tablets. Both strengths correspond to the immediate-release tablets that are licensed in the UK, which are normally taken twice a day rather than once.

The usual starting amount is 75 mg a day in two divided doses with food, for example 37.5 mg in the morning and 37.5 mg in the evening. If the response is not sufficient, the prescriber may increase the daily dose, generally at intervals of two weeks or more (never sooner than four days), up to a maximum of 375 mg a day. Each increase should follow a clinical review, because several side effects rise with the dose. Treatment for depression usually lasts several months and continues for at least six months after symptoms have settled. In mild or moderate liver disease the dose is often halved, and a 50% reduction also applies in severe kidney impairment or haemodialysis. Someone who takes 37.5 mg twice daily can later be moved to a once-daily prolonged-release form of the same total amount.

Venlafaxine is a prescription-only medicine (POM) in the UK. Generic immediate-release tablets come in 37.5 mg and 75 mg strengths, and there is also an oral solution. Once-daily prolonged-release capsules and tablets are sold under names such as Efexor XL, Vencarm XL, Venaxx XL, Venladex XL and Sunveniz XL. The prescriber decides which form and dose are appropriate.

It must not be taken together with an irreversible MAOI; at least 14 days are needed after stopping such a medicine before starting, and at least 7 days after the last dose before an MAOI is begun. The SmPC reports dose-related rises in blood pressure, so readings are taken before treatment and checked regularly, and heart rate can also increase. Other cautions include raised eye pressure or a risk of angle-closure glaucoma, epilepsy, bipolar disorder, bleeding problems or anticoagulant use, and low sodium, particularly in older people. Serotonin syndrome may occur when combined with triptans, tramadol, lithium, St John’s wort, other antidepressants or linezolid. Young adults should be watched closely for suicidal thoughts in the early weeks.

Very common reactions include nausea, a dry mouth, headache and sweating, including night sweats. Dizziness, sleeping difficulties, constipation, loss of appetite, blurred vision and sexual problems are also frequently reported. Stopping suddenly can cause dizziness, electric-shock sensations, nausea, anxiety and sleep disturbance, so the dose is lowered gradually over at least one to two weeks, and for some people over several months.