Serotonin Norepinephrine Reuptake Inhibitors – Drug Study & Nursing Implications

Serotonin Norepinephrine Reuptake Inhibitors

SNRIs (Serotonin Norepinephrine reuptake inhibitors)


SNRIs are antidepressants which work by inhibiting both serotonin and norepinephrine reuptake transporter. SNRIs are the most prescribed antidepressants now a days.

Class Generic Name Brand Name


SNRIs (Serotonin nor epinephrine reuptake inhibitors)

Venlafaxine Effexor
Desvenlafaxine Desfax, Pristiq, Ellefore







SNRIs work by elevating certain 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.

SNRIs work 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.


SNRIs are orally active drug, absorb in the body through digestion. The average half-life of SNRIs is 5 hours. Some drugs have active metabolites. Venlafaxine and trazodone have short plasma half-life and required divided doses.




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.



Hepatic failure

Renal failure


Coronary artery disease

Eating disorder (bulimia or anorexia)

Uncontrolled narrow angle glaucoma (duloxetine and milnacipran)



Manic episodes

Decrease libido

Weight gain


Increase in anxiety


Sexual side effects include erectile dysfunction




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


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

Nefazodone is contraindicated with other serotogenic antidepressants.

Cimetidine may increase the plasma level of venlafaxine and duloxetine.

The concurrent use of venlafaxine and propafenone may cause psychosis

Duloxteine is contraindicated with concurrent use of MAOI and SSRIs.

Ciproflozacina, enoxacin and quinidine may increase the plasma levels of duloxetine.

Duloxetine may increase the levels of thioridazine and flecainide

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.


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.



IF taken MAOIs, forbid patient to take any fermented or aged food or containing tyramine.

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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