SSRI's Vs. SNRI's—What's The Diff?
Antidepressant drugs do their work by either increasing the production of neurotransmitters or by breaking them down. There are three major neurotransmitters that are involved in depression. These are called dopamine, norepinephrine, and serotonin. Serotonin is sometimes called 5-HT.
When the levels of one or more of these neurotransmitters dip or become unbalanced, depression or other conditions may result. The newest class of antidepressants is called selective serotonin and norepinephrine reuptake inhibitors (SNRI's). The drugs from this class used for depression are Effexor XR (venlafaxine), Cymbalta (duloxetine), and Pristiq (desvenlafaxine).
SNRI's are capable of acting on both norepinephrine and serotonin. Low levels of these two neurotransmitters are known to be a factor in depression. However, norepinephrine affects energy levels and level of alertness, while serotonin's sphere of influence is on mood. Because of this unique dual action in raising levels of both serotonin and norepinephrine, SNRI's combat more than one cause of depression.
In treating depression, the doctor's aim is to achieve remission in the depressed patient. The medical director of Georgia Institute of Mood and Anxiety Disorders, Dr. Jeffrey Kelsey says that all the antidepressants available on today's U.S. market are equal in their effectiveness. "However, when it comes to remission, the data shows that SNRIs, dual-acting antidepressants, will, in some patients, confer an advantage. And the tricky part is going into it; we don't know which patients will benefit from one approach to the other. SSRIs are very effective treatments but some patients are going to get more benefit from a dual-acting antidepressant," says Kelsey.
The FDA has approved Cymbalta, Effexor XR, and Pristiq for the treatment of major depressive disorder (MDD). The first two have also been approved for treating generalized anxiety disorder (GAD), a known associated condition for depression. Cymbalta is also indicated for relief from diabetic peripheral neuropathic pain, a condition secondary to nerve damage incurred by diabetes. Besides MDD and GAD, Effexor XR has been approved for the treatment of panic disorder and for treating social anxiety disorder.
Cymbalta and Effexor XR have been found to have comparable rates of effectiveness. In two studies, patients were treated with 60 mg of Cymbalta daily or 150 mg of Effexor XR over a period of 6 weeks. Then patients continued to take the same drug for a further 6 weeks but with doses adjusted to a maximum of 120 mg daily for Cymbalta and 225 mg daily for Effexor XR. 75% of the Effexor XR group completed the entire 12 weeks of treatment as opposed to 65% of those taking Cymbalta. Cymbalta caused greater nausea and a small number of those in the Effexor XR group had heightened blood pressure.