The quality of evidence is downgraded by limitations in study quality (unclear allocation concealment and high loss to follow-up in relation to observed absolute effect).
A Cochrane review included 18 studies with a total of 6 406 subjects. 6 studies (n=2 249) tested duloxetine for fibromyalgia, 2 for 12 weeks and 1 for 6 months. Duloxetine at 60 mg daily was effective in fibromyalgia over 12 weeks (RR for ≥ 50% reduction in pain 1.57, 95% CI 1.20 to 2.06; NNTB 8, 95% CI 4 to 21) and 28 weeks (RR 1.58, 95% CI 1.10 to 2.27). A dose of 20 mg was not effective and a higher dose of 120 mg was no more effective than 60 mg.
Adverse events were analysed across all included studies (studies included patients with fibromyalgia or with painful peripheral neuropathy). Adverse events were common in both treatment and placebo arms but more common in the treatment arm with a dose dependent effect. Most side effects were minor, but 12.6% of participants stopped the drug due to side effects. Serious adverse events were rare.
| Outcomes | Number of participants (studies) | Assumed risk (control) | Corresponding risk (duloxetine 60 mg) | Relative effect RR (95% CI) | NNT /NNH (95% CI) |
|---|---|---|---|---|---|
| * includes patienst with fibromyalgia or painful peripheral neuropathy | |||||
| Greater than 50% improvement of fibromyalgia pain | 528 (2) | 233 per 1000 | 366 per 1000 | 1.6 (1.2 to 2.1) | 8 (5 to 17) |
| Adverse event leading to cessation* | 4 837 (14) | 56 per 1000 | 109 per 1000 | RR 1.95 (1.6 to 2.4) | 18 (13 to 30) |
Another Cochrane review on serotonin and noradrenaline reuptake inhibitors (SRNIs) included 10 studies with a total of 6 038 subjects. 5 studies (n=1 941) investigated duloxetine (60 or 120 mg) against placebo. Duloxetine had a small beneficial effect over placebo on pain, fatigue, sleep problems, and disease-related quality of life (table ). The dropout rate due to adverse events in the duloxetine group was higher than in placebo group. There was no statistically significant difference in serious adverse events between duloxetine and placebo.
| Outcome | Participants (studies) | Assumed risk (placebo) | Corresponding risk (duloxetine, 95% CI) | Effect size (95% CI) |
|---|---|---|---|---|
| *favours duloxetine | ||||
| 50% pain reduction | 1 884 (5) | 210 per 1000 | 333 per 1000 (283 to 394) | RR 1.59 (1.35 to 1.88) |
| Pain | 1 925 (5) | SMD –0.32 (–0.41 to –0.22) | ||
| Fatigue | 1 568 (4) | SMD –0.12 (–0.23 to –0.02) | ||
| Sleep problems | 996 (2) | SMD –0.24 (–0.37 to –0.12) | ||
| Disease-related quality of life | 1 380 (4) | SMD –0.27 (–0.39 to –0.15)* | ||
| Withdrawal due to adverse events | 1 941 (5) | 113 per 1000 | 187 per 1000 (152 to 236) | RR 1.65 (1.30 to 2.09) |
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