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.