A Cochrane review measured the effect of quetiapine on fibromyalgia symptoms «Walitt B, Klose P, Üçeyler N, et al. Antipsychotic...»1. The study measured only dichotomized outcomes on pain relief, which decreases the applicability of the estimates. The risk difference for 30 % pain reduction was 0.12 (95 % CI 0.00-0.23). The largest trial suggested 0.6 points decrease in pain severity (95 % CI -1.2 to 0.0, scale 0-10) «McIntyre A, Paisley D, Kouassi E, et al. Quetiapin...»2. The review suggested also a decrease in sleep problems (SMD -0.67, 95% CI -1.10 to -0.23), depression symptoms (SMD -0.39, 95% CI -0.74 to -0.04), and anxiety (SMD -0.40, 95% CI -0.69 to -0.11).

Quetiapine increased the risk of weight gain (risk difference [RD] 0.08, 95% CI 0.02 to 0.15). Indirect evidence treatment of schizophrenia suggest that quetiapine also increases sleepiness (RD 7 %), dizziness (RD 5 %), dry mouth (RD 5 %), and may also increase the risk of constipation (RD 4 %) «Srisurapanont M, Maneeton B, Maneeton N. Quetiapin...»3.

The level of evidence was downgraded due to study limitations, imprecision and indirectness (the largest trial included only patients with severe depression).

Study 1

In a systematic Cochrane review «Walitt B, Klose P, Üçeyler N, et al. Antipsychotic...»1 CENTRAL (2016, Issue 4), MEDLINE and EMBASE to 20 May 2016 were searched, together with reference lists of retrieved papers and reviews and two clinical trial registries, to assess the efficacy, tolerability and safety of antipsychotics in fibromyalgia in adults. Trial authors were also contacted. Trials of at least four weeks duration of any formulation of antipsychotics used for the treatment of fibromyalgia in adults were included. A total of four studies with 296 participants were included in the review. Three studies with 206 participants compared quetiapine, an atypical (second-generation) antipsychotic, with placebo. One study used a cross-over design and two studies a parallel-group design. Study duration was eight or 12 weeks. Quetiapine was used in all studies with a bedtime dosage between 50 and 300 mg/day. All studies had one or more sources of potential major bias and were judged to be at moderate risk of bias overall. The primary outcomes in review were participant-reported pain relief of 50% or greater, Patient Global Impression of Change (PGIC) much or very much improved, withdrawal due to adverse events (tolerability) and serious adverse events (safety).

Quetiapine did not increase the number of patients with 50 % pain reduction. No study reported data on PGIC. A greater proportion of participants on quetiapine reported a 30% or more pain reduction (risk difference (RD) 0.12, 95% confidence interval (CI) 0.00 to 0.23; number needed to treat for an additional benefit (NNTB) 8, 95% CI 5 to 100). A greater proportion of participants on quetiapine reported a clinically relevant improvement of health-related quality of life compared to placebo (RD 0.18, 95% CI 0.05 to 0.31; NNTB 5, 95% CI 3 to 20). Quetiapine was superior to placebo in reducing sleep problems (standardised mean difference (SMD) -0.67, 95% CI -1.10 to -0.23), depression (SMD -0.39, 95% CI -0.74 to -0.04) and anxiety (SMD -0.40, 95% CI -0.69 to -0.11). Quetiapine was superior to placebo in reducing the risk of withdrawing from the study due to a lack of efficacy (RD -0.14, 95% CI -0.23 to -0.05) (very low quality evidence). There was no significant difference between quetiapine and placebo in the proportion of participants withdrawing due to adverse events (tolerability, in the frequency of serious adverse events (safety) and in the proportion of participants reporting dizziness and somnolence as an adverse event. In more participants in the quetiapine group a substantial weight gain was noted (RD 0.08, 95% CI 0.02 to 0.15; number needed to treat for an additional harm (NNTH) 12, 95% CI 6 to 50) (very low quality evidence). The authors downgraded the quality of evidence by three levels to a very low quality rating because of limitations of study design, indirectness (patients with major medical diseases and mental disorders were excluded) and imprecision (fewer than 400 patients were analysed).

Studies with other antipsychotics than quetiapine in fibromyalgia were not found at the moment of this systematic review (2016).

As a conclusion, very low quality evidence suggests that quetiapine may be considered for a time‐limited trial (4 to 12 weeks) to reduce pain, sleep problems, depression and anxiety in fibromyalgia patients with major depression. Potential side effects such as weight gain should be balanced against the potential benefits in shared decision making with the patient.