Effexor XR (Venlafaxine). Dosage, Side Effects, Interactions
Effexor XR (Venlafaxine) is an antidepressant and serotonin-norepinephrine reuptake inhibitor. Venlafaxine is used to treat depression, anxiety and panic disorders in adults.
Effexor XR (Venlafaxine) is used in adult patients for drug treatment or prevention of recurrence of depression , generalized anxiety disorder, social phobia and panic disorders with or without agoraphobia.
How Effexor XR (Venlafaxine) works
The active ingredient belongs to the group of serotonin-norepinephrine reuptake inhibitors (SNRI) . The effect of venlafaxine is based on the selective inhibition of the reuptake of the messenger substances norepinephrine and serotonin in the presynaptic neuron. The reuptake of the messenger substance dopamine is only slightly inhibited by venlafaxine. Inhibition means an increase in neurotransmitter activity in the central nervous system.
At least 92% of venlafaxine is absorbed by the body after oral administration. The absolute bioavailability is 40 to 45% as the active substance is primarily converted to the active metabolite O-desmethyl-venlafaxine. Peak plasma levels are reached about two to three hours after ingestion. If the active substance comes from slow-release capsules, it can take up to nine hours before peak values can be measured in the plasma. Steady-state concentrations are reached within three days of multiple oral dosing. Venlafaxine is metabolised in the liver and excreted mainly renally. Two days after ingestion, about 87% of the active ingredient is excreted.
Dosage of Effexor XR (Venlafaxine)
Venlafaxine is taken with a meal once a day, if possible at the same time. Depending on the indication, different dosages are recommended.
Major Depressive Episodes
The starting dose of 75 mg/day divided into two to three single doses can be increased every two weeks. The maximum recommended daily dose is 375 mg.
Generalized Anxiety Disorder
The starting dose of 75 mg/day once a day can be increased every two weeks. The maximum recommended daily dose is 225 mg.
Social Anxiety Disorder
The starting dose of 75 mg/day once daily should not be increased as there is no evidence that higher doses are of additional benefit to the patient in social anxiety disorder. Only patients who do not respond to the initial dose may increase it to up to 225 mg per day. The dose should be increased in two-week increments.
Patients should take venlafaxine prolonged-release 37.5 mg daily for seven days. If they do not respond, the dose can be increased up to 225 mg per day, but gradually at least every two weeks.
Antidepressant therapy should last at least six months, even if remission has already started. Treatment should be reviewed periodically.
Side effects of Effexor XR (Venlafaxine)
As with all medicines, undesirable effects can also occur after taking venlafaxine, even if the active substance is better tolerated than older antidepressants. The most common side effects of venlafaxine are nausea, headache, drowsiness, insomnia, sweating, and dry mouth. The side effects are listed below in order of frequency.
- dry mouth
- decreased appetite
- unusual dream content
- libido decrease
- visual disturbances
- accommodation disorders
- rise in blood pressure
- hot flashes
- skin rash
- muscle hypertonia
- delayed urination
- urinary retention
- erectile dysfunction
- ejaculation disorders
- weight loss
- weight gain
- increased cholesterol levels.
- orgasmic disorders
- balance disorders
- coordination disorders
- orthostatic hypotension
- gastrointestinal bleeding
- changes in liver values
- small skin hemorrhages
- hypersensitivity to light
- urinary incontinence.
- aplastic anemia
- anaphylactic reactions
- Syndrome of inappropriate ADH secretion
- Neuroleptic Malignant Syndrome
- Serotonin Syndrome
- angle- closure glaucoma
- Torsades de pointes
- ventricular tachycardia
- ventricular fibrillation
- QT prolongation
- interstitial pneumonia
- pulmonary eosinophilia
- Stevens-Johnson Syndrome
- toxic epidermal necrolysis
- erythema multiforme
Since venlafaxine is metabolised by CYP2D6 , its potential for drug-drug interactions is relatively high. Interactions with:
- Monoamine Oxidase Inhibitors (MAOIs)
- Reversible selective MAO-A inhibitors (moclobemide)
- Reversible Nonselective MAOI ( Linezolid )
- Other serotonergic agents
- CNS active substances
- Substances that prolong the QT interval
- indinavir .
Any alcohol consumption should be avoided if venlafaxine is taken at the same time.
There is no clear evidence that venlafaxine reduces the effectiveness of oral contraceptives, however, unintended pregnancies that have occurred during venlafaxine therapy have been reported.
Drugs containing venlafaxine should not be taken if:
- Hypersensitivity to the active substance or to any of the medicinal components
- concomitant use of MAO inhibitors
- children under the age of 18.
Venlafaxine reduced fertility in animal studies, but the significance of this study result for humans is unknown. There are no adequate data from the use of venlafaxine in pregnant women. The active substance may only be used in them if the expected benefit outweighs the possible risks. Discontinuation symptoms may occur in newborn babies if the drug is taken until shortly before birth. Since venlafaxine is excreted in human milk and a risk to the breast-fed child cannot be excluded, the decision to take venlafaxine during breast-feeding should be carefully considered.
Venlafaxine may impair judgement, thinking and motor skills. The ability to drive or operate dangerous machinery may be reduced during therapy.
Further details on this active ingredient can be found in the relevant product information.
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