FDA approves Cymbalta to treat neuropathic Fibromyalgia pain

The U.S. Federal Drug Administration (FDA) this week approved the drug duloxetine HCl, sold under the name Cymbalta, for treatment of the widespread pain associated Fibromyalgia (FM).

Cymbalta has been in use as an anti-depressant since the mid-1990’s, but new test results indicate that the drug can also play a role in relieving the type of neuropathic pain commonly experienced by fibromyalgia patients. Cymbalta was originally developed by the Eli Lilly pharmaceutical corporation for use as a selective serotonin and norepinephrine re-uptake inhibitor (SNRI), a class of antidepressants meant to improve upon the previous selective serotonin re-uptake inhibitors (SSRI’s) such as Paxil, Prozac, and Zoloft. The drug works on both serotonin and norepinephrine, neurotransmitters known to be involved in both the regulation of moods and the experience of pain. These antidepressants increase the amount of neurotransmitters in the body’s circulation (think of “re-uptake” as recycling; once a neurotransmitter acts on the nerve, it is re-distributed back into the brain for further use rather than being absorbed and broken down by the body). Although SSRI’s are generally thought to produce fewer side effects because they only work on serotonin, some patients respond better to drugs which target both neurotransmitters at once.

Data Highlights

Lilly established the efficacy of Cymbalta in two pivotal three-month clinical trials involving 874 patients with fibromyalgia. In both studies, Cymbalta reduced pain at study endpoint compared with placebo as measured by the Brief Pain Inventory (BPI) 24-hour average pain scale.(vi),(vii) The BPI is a scale that measures the severity of pain.

Significant improvement in pain for Cymbalta vs. placebo was observed in the first week of each study. Fifty-one percent and 55 percent of patients on Cymbalta had a 30 percent improvement on the BPI at endpoint (clinically meaningful relief is considered at least 30 percent pain reduction(viii)).

In addition, 65 percent and 66 percent of patients taking Cymbalta 60 mg daily reported feeling better at endpoint as measured by the Patient Global Impression of Improvement (PGI-I). The PGI-I is a patient-rated scale that evaluates how much improvement has occurred since beginning treatment.

Cymbalta 60 mg was superior to placebo on the Fibromyalgia Impact Questionnaire (FIQ) Total Score. The FIQ is a scale that is used to assess and evaluate the impact of fibromyalgia on aspects of health and functioning believed to be most affected by the disorder.

In four pooled studies, the most commonly observed adverse events in Cymbalta-treated patients with fibromyalgia (greater than or equal to 5 percent and at least twice placebo) were nausea (29 percent), dry mouth (18 percent), constipation (15 percent), decreased appetite (11 percent), sleepiness (11 percent), increased sweating (7 percent) and agitation (6 percent). In the placebo-controlled clinical trials, the overall discontinuation rates due to adverse events for Cymbalta vs. placebo were 20 percent and 12 percent, respectively…

Although Cymbalta has been safely used for years, it has not escaped controversy. Serious side effects can occur in patients taking the drug, particularly if prescribers fail to consider or are unaware of potentially harmful interactions with other medications. In 2007 the FDA issued a warning against using SSRI or SNRI antidepressants with certain medications commonly prescribed for migraine headaches. However, many patients are finding the relief the drug provides from both pain and depression to be worth the risks. As with any medication, the potential risks and benefits should be discussed with a qualified physician who is aware of all medications the patient may be taking in order to minimize the risk of side effects and drug interactions.