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Fibromyalgia 205
Fibromyalgia pain does not result from peripheral nociceptor stimulation
but instead arises from deficient CNS processing and modulation of pain
signals. Consequently, centrally acting medications form the mainstay of the
management of chronic fibromyalgia pain. 1 Fortunately, management decisions
in this challenging disease can be informed by results from a number of
studies assessing myriad analgesic approaches.
Tricyclic antidepressants (TCAs) and related drugs have some efficacy
when compared with placebo in clinical trials. The best evidence exists for
cyclobenzaprine (30–50 mg/day), which in five clinical trials showed a 20%
response rate (i.e. need to treat 4.8 patients to achieve significant pain relief
in a single subject). 2 Several studies have demonstrated that low-dose amitriptyline
(25–50 mg/day) produces significant pain score reductions compared
with placebo controls, in 25–45% of patients. 3–5 Utility of TCAs is
limited by a high (> 50%) rate of nonresponse to both cyclobenzaprine and
amitriptyline. Furthermore, the side effect profile of TCAs (e.g. drowsiness,
dry mouth, constipation, edema, weight gain) in fibromyalgia patients contributes
to rates of medication self-discontinuation that approach 50% in the
first 12 months of therapy. 6,7
There is mixed evidence regarding antidepressants other than TCAs for
fibromyalgia pain relief. Fluoxetine and duloxetine are the most extensively
studied SSRIs. One multicenter trial found no pain relief with duloxetine
compared with placebo, but another placebo-controlled trial found modest
pain score reductions. 8,9 Considering the available data, it seems likely that
there is some role for duloxetine (60 mg QD, titrated to 60 mg PO BID) in
fibromyalgia. 10
Fluoxetine outperforms placebo in RCTs but only when given in a highdose
(80 mg/day) regimen. 11,12 However, one trial suggests that adding lowdose
fluoxetine (20 mg/day) to a TCA (amitriptyline 25mg/day) yields better
pain relief than that which is achieved with TCA monotherapy. 13 Other
antidepressants (e.g. desipramine, citalopram, venlafaxine, milnacipran,
bupropion) have been studied for treating fibromyalgia pain, but there is
currently no basis for recommending acute care use of these drugs. 14–17
In addition to TCAs and other antidepressants, the other commonly seen
approach to treating fibromyalgia pain is the use of anticonvulsants.