SNRI (Serotonin-Norepinephrine Reuptake Inhibitor) Antidepressants

SNRI antidepressants are a relatively new class of antidepressants that affect both serotonin and norepinephrine uptake. Neurotransmitters, like serotonin and norepinephrine are found in the "synaptic cleft," the space between nerve cells (neurons). These chemicals are instrumental in transmitting information from once cell to another, and different transmitters transmit different messages. Neurotransmitters usually have multiple functions, and they work together to produce certain effects.

Both serotonin and norepinephrine seem to help regulate mood. An older class of antidepressants, the tricyclics, also affect serotonin and norepinephrine, along with other neurotransmitters. Most of the side effects that people experience when taking tricyclics come from the overlapping effect on other neurotransmitters, like histamine and acetylcholine. One of the objectives of neuropharmaceutical research has been to create medications that only act on the desired neurotransmitters, thus eliminating many of the undesirable side effects.

SSRI's target only serotonin, but they do have some overlap with other neurotransmitters. You get a dry mouth or constipation because acetylcholine is involved, and sleepiness comes from the effect on histamine. SNRI's seem to hit the target neurotransmitters a bit more specifically, which means fewer side effects.

Serotonin seems to help regulate mood. Norepinephrine regulates mood and seems to be involved in pain perception, motivation and concentration. Pain and depression are closely related, and it is becoming apparent that SNRI's have a role in treating both depression and managing chronic pain.

The only true SNRI's currently available in the US are venlafaxine (Effexor, Effexor XR) and duloxetine (Cymbalta). Desvenlafaxine succinate (Pristig) recently received a letter of approval from the FDA and will be available soon.

Uses for SNRI's

SNRI antidepressants are approved to treat the following conditions:

They are often used to treat other chronic pain syndromes, such as fibromyalgia, migraines, back pain, neuropathic pain and irritable bowel syndrome.

Common side effects

SNRI antidepressants seem to have fewer side effects than previous types of antidepressants. The most common ones are:

Drug interactions

SNRI's can interact with the following medications:

Problems with SNRI's

Discontinuation syndrome: Like SSRI's, SNRI's are not addictive but they do cause withdrawal symptoms if you stop taking them abruptly. Discontinuation symptoms include aches and pains, flu-like symptoms and restlessness. SNRI's are usually discontinued gradually.

Suicide and aggression: There is concern with all antidepressants that there may be an increased risk for suicide when taking them, especially in the first few weeks. Anyone who begins taking antidepressants should be monitored closely for several weeks or months with weekly visits to a physician or therapist. Friends and family are encouraged to monitor the person on a daily basis for the first few weeks, and any evidence of increasing depression, suicidal thoughts, hostility and anger or unusual behavior should be reported to the physician immediately.

Mania: Antidepressants taken alone (without mood stabilizers) can trigger manic episodes in people with bipolar disorder.

Pregnancy and lactation: The safety of SNRI's during pregnancy has not been determined and each situation has to be evaluated individually. SNRI's are excreted in breast milk, and breastfeeding is not recommended while taking them.

Overdose: Overdose of SNRI's usually causes nausea and vomiting, but is rarely fatal unless very large doses are taken.

Serotonin Syndrome: Serotonin Syndrome is caused by excess serotonin levels. This is most likely to happen when more than one serotonergic medication is taken at the same time. Nearly all antidepressants affect serotonin; thus, other antidepressants are not usually taken along with an SNRI. A few antidepressants have very long-lasting effects, and it is important not to take an SNRI for up to two weeks after discontinuing an MAOI antidepressant. Many other medications affect serotonin, so it is important to make sure that your physician and pharmacist know about all of the medications you take.

Serotonin Syndrome symptoms can range from mild tremors, sweating and anxiety to high fever, multiple organ failure and death.