Serotonin/Norepinephrine Reuptake Inhibitors

Serotonin and norepinephrine reuptake inhibitors, called SNRIs, are similar to the SSRIs. Their therapeutic actions make them useful for treating major depression, social anxiety disorder, and generalized anxiety disorder.

Prototype and Other Medications

Venlafaxine is the prototype for the SNRIs. Other SNRIs include desvenlafaxine and duloxetine.

Expected Pharmacologic Action

SNRIs block the neuronal reuptake of both serotonin and norepinephrine without having a major impact on other receptors or neurotransmitters. Thus, they increase the amount of serotonin and norepinephrine available in the brain for nerve impulse transmission. Ultimately, these actions reduce depression manifestations.

Adverse Drug Reactions

SNRIs share many of the same adverse effects as SSRIs. The most common adverse effect of SNRIs is nausea. These medications also cause vomiting, anorexia, headache, hypertension, insomnia, and nervousness. Hyponatremia, especially in older adults and those taking diuretics, is also possible. Stopping the medication abruptly can cause anxiety, agitation, headache, and tachycardia. As with other antidepressants, there is an increased risk of suicide, particularly in children and young adults.

Interventions

For clients taking an SNRI, monitor for nausea and other gastrointestinal effects, and suggest that clients who develop these effects take the medication with food. Check for weight loss related to anorexia and monitor blood pressure. Monitor for insomnia and nervousness. A lower dosage might help these manifestations resolve. Gradually withdrawing clients from SNRI use over a period of 2 to 4 weeks will reduce the intensity and duration of withdrawal manifestations, which typically include anxiety, tremors, headache, tachycardia, nausea, tinnitus, and vertigo. Finally, make sure clients understand that these mediactions can increase the risk of suicide and that they should report any worsening of depression or thoughts of suicide.

Administration

Begin administration of the prototype SNRI, venlafaxine, with low doses and titrate upward every 4 days until clients are taking the optimal dosage. Clients should take SNRIs with food to minimize gastrointestinal manifestations. It is essential that they swallow sustained-release capsules whole and do not crush or chew them.

Client Instructions

When instructing clients about taking SNRIs, make sure they understand to take the medication with food to avoid or minimize gastrointestinal upset. Tell them to report headache, insomnia, and nervousness. For headaches, they can try over-the-counter analgesics such as acetaminophen. For insomnia, tell them to schedule doses as far ahead of bedtime as possible. Generally, doses are divided, so it may not be possible to avoid giving a dose in the late afternoon or early evening. Due to the risk for hypertension, tell clients to have their blood pressure checked regularly. Make sure clients know not to stop taking the medication abruptly because this can cause withdrawal manifestations.

Safety Alert

The risk of suicide when clients take antidepressants may increase during the initial phase of treatment. This is particularly true for children and young adults. Be sure to inform clients and families about this side effect, and make sure they report any worsening of depression or thoughts of suicide. Monitor these clients closely during this time to prevent any suicide attempts.

Contraindications and Precautions

Contraindications to SNRIs are a history of hypersensitivity to SNRIs, suicidal ideation, and concurrent use of MAOIs or within 14 days of last dose. Use these medications with caution for clients who have liver or kidney disease, glaucoma, cardiac disorders, or hypertension.

Interactions

Taking SNRIs within 2 weeks of MAOIs increases the risk of serotonin syndrome. Cimetidine, desipramine, and haloperidol increase blood levels of venlafaxine. Trazodone and the herbal supplements St. John’s wort and sour date nut increase the risk of serotonin syndrome.