Venlafaxine – Drug Study & Nursing Implications

VENLAFAXINE

GENERAL DESCRIPTION

Venlafaxine is the first SNRIs that is used commonly in depression and anxiety disorders. Venlafaxine is a potent inhibitor of serotonin transporter and a weak norepinephrine transport. At low doses it behaves same as SSRIs but at high doses it increase blood pressure and heart rate.

GENERIC NAME: Venlafaxine

BRAND NAME: Effexor

MECHANISM OF ACTION

Venlafaxine works by elevating serotonin and norepinephrine neurotransmitter in the brain. At presynaptic serotonergic neuron, this interact with postsynaptic neuron which have postsynaptic receptors which are 5-HT. serotonin is synthesized from amino acid tryptophan by serotonergic neurons. These serotonin is stored in vesicles for regulated release.

At presynaptic noradrenergic neuron, this interact with postsynaptic neuron which have postsynaptic receptors which are β and α1. Norepinephrine is synthesized from amino acid tyrosine by noradrenergic neurons and stored in vesicles awaiting regulated release.

When serotonin and NE release from the neuron they stimulate their receptors and at the same time they transported back to their neurons by a process called reuptake. Serotonin is reuptake by serotonin transporter or SERT and norepinephrine is transported back to their neuron by norepinephrine transporter or NET. Once both chemicals reabsorb they partially repacked in synaptic vesicles in partially broken down into inactive metabolites by an enzyme monoamine oxidase or MAO.

Venlafaxine works by inhibiting both serotonin and norepinephrine reuptake transporter i.e. SERT and NET, which result in increased levels of both serotonin and norepinephrine which can then bind to their respective postsynaptic receptors.

PHARMACOKINETICS

Venlafaxine achieved steady state plasma levels within 3 days. It has 27-30% protein binding. The elimination half-life of parent venlafaxine is 5 hours and its active metabolite desmethyl venlafaxine has 11 hours. Desmethyl venlafaxine is excreted by hepatic metabolism and renal excretion.

INDICATIONS

Depression

Chronic musculoskeletal pain

Anxiety and panic disorders

Obsessive compulsive disorder

Attention deficit hyperactivity disorder

Menopausal symptoms relief

Reducing pain associated fibromyalgia and other pain caused by neuropathy. It is due to enhance noradrenergic activity in the central nervous system.

CONTRAINDICATIONS

Hypertension

Hepatic failure

Renal failure

Alcohol

Coronary artery disease

Eating disorder (bulimia or anorexia)

MAOIs

SIDE EFFECTS & ADVERSE EFFECTS

Manic episodes

Decrease libido

Weight gain

Insomnia

Increase in anxiety

Irritability

Sexual side effects include erectile dysfunction

Nausea

Vomiting

Diarrhea

Abrupt with drawl may cause temporary deficiency of serotonin which may lead to headache, nausea, vomiting, agitation, sleep disturbance.

Serotonin syndrome

Increase blood pressure and heart rate

DRUG INTERACTION

Nefazodone may cause acute hypotension and weakness when given with venlafaxine.

Cimetidine may increase the plasma level of venlafaxine.

The concurrent use of venlafaxine and propafenone may cause psychosis

The concurrent use of venlafaxine with co-amoxiclav or dexamphetamine or metoclopramide or tramadol may cause serotonin syndrome.

Diphenhydramine, melperone, quinidine, thioridazine may inhibit the metabolism of venlafaxine.

Venlafaxine and disulfiram may cause hypertensive crisis.

Venlafaxine may increase the antimuscarinic effects of TCAs.

NURSING INTERVENTIONS

Enquire the complete health history of the patient including allergy, drug interactions, and family background of depression

Check lab test for CBC, blood glucose, BUN, creatinine, platelets, electrolytes, LFT

Check and identify if any neurological disorder like seizure etc

Monitor blood pressure and pulse before and during treatment

Administer medicine at night or bed time to avoid drowsiness at day time

Observe mood swing during the treatment

Observe s/s for serotonin syndrome, if any

Observe cardiovascular or neurologic s/s for any disorder, if any

Avoid to administer MAOIs with tyramine containing food

Observe sleep-wake cycle of the patients.

PATIENT EDUCATION

Advise to take medicine at night or bed time to avoid drowsiness at day time and take morning dose early to avoid insomnia.

Advise patient not to discontinue treatment because it may take 2-4 weeks to start antidepressant effects

Inform the patients about the possible side effects of medication specially serotonin syndrome which may be life threatening.

Report immediately if feeling bradycardia, urinary retention, blurred vision, chest pain, and diaphoresis.

Advice to take care and slow change of posture due to dizziness and danger of fall or injuries.

Avoid driving if feeling drowsiness or dizziness.

Do not breast breast feed while taking medicine.

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