SNRIs

Summary

SNRIs include the drugs duloxetine, venlafaxine, and desvenlafaxine. They work by inhibiting the reuptake of both serotonin and norepinephrine, increasing their levels in the brain. Clinically, SNRIs are used to treat conditions like depression, anxiety, panic disorder, and neuropathic pain.

Common side effects include sexual dysfunction, nausea and vomiting, hypertension, and insomnia. Because they alter serotonin levels, SNRIs can cause serotonin syndrome. Patients on SNRIs should avoid taking MAOIs, St. John's Wort, and alcohol due to the risk of interactions. If stopping an SNRI, it must not be stopped abruptly, but instead tapered down gradually under medical supervision.

Key Points

• Serotonin Norepinephrine Reuptake Inhibitors (SNRIs)
  • Drug Names
    • Duloxetine (Cymbalta)
    • Venlafaxine (Effexor)
    • Desvenlafaxine (Pristiq)
  • Mechanism
    • Inhibits reuptake of serotonin and norepinephrine
      • This increases the amount of serotonin and norepinephrine in the synaptic cleft
  • Clinical Use
    • Depression
    • Anxiety
      • Panic disorders
      • Generalized Anxiety Disorder (GAD)
      • Social anxiety disorder
    • Neuropathic pain
      • Including fibromyalgia and diabetic neuropathy
  • Side Effects
    • Insomnia
      • SNRIs often cause CNS stimulation, making it hard to sleep
    • Sexual dysfunction
      • Extremely common side effect
      • Often presents as decreased libido or erectile dysfunction
    • Serotonin Syndrome
      • Can be thought of as a “serotonin overdose” - there is too much serotonin in the synaptic cleft
      • Manifestations include fever, diaphoresis (sweating), tachycardia, tremors, altered mental status, GI distress, and muscle rigidity or spasms
    • Nausea/vomiting
    • Hypertension
  • Interactions
    • Avoid MAOIs
      • Increases risk for serotonin syndrome
    • Avoid St John’s Wort
      • Increases risk for serotonin syndrome
    • Avoid alcohol
  • Administration
    • Do not stop abruptly
      • The drug must be tapered off over time to prevent withdrawal symptoms
      • Withdrawal symptoms include sensory disturbances, GI upset, and insomnia