Background: The investigator hypothesized that the combined use of pregabalin and paroxetine would be associated with comparable Somatic Symptoms Scale-8 (SSS-8) and higher tolerability than amitriptyline or venlafaxine.

Methods: After ethical approval, 75 patients with diagnosed fibromyalgia who were receiving pregabalin 75 mg/day, were randomly allocated to receive amitriptyline 25 mg/day (n = 24), venlafaxine 75 mg/day (n = 25), or paroxetine 25 mg/day (n = 26). All patients were assessed bi-monthly for consequent six months for the changes in the SSS-8, Center for Epidemiological Studies Depression Scale (CESDS), life satisfaction, mood, sleep quality, fatigue and medication tolerability and adverse effects.

Fibromyalgia is a common cause of chronic widespread disabling pain affecting 2-5% of the young to middle-aged women in developed countries. The American College of Rheumatology has been established new diagnostic criteria for fibromyalgia in 2010 included a widespread pain index (WPI) and categorical scales for cognitive symptoms, unrefreshed sleep, fatigue, and number of somatic symptoms. The definite pathophysiology of chronic pain in fibromyalgia remains unclear.

Fibromyalgia is usually associated with depression, anxiety, and alexithymia increasing over age which contribute significantly to reduced patient wellbeing. These may be due to alterations of central pain pathways, hyporeactivity of the hypothalamus-pituitary-adrenal axis, and disturbances in the dopaminergic and serotonergic systems. Thus the European League Against Rheumatism (EULAR) recommends the use of serotonin and noradrenaline reuptake inhibitors (SNRIs) for the treatment of fibromyalgia, to reduce pain and improve function.

However, few patients achieve satisfactory pain relief with the sole use of SNRIs. A recent Cochrane review demonstrated only modest improvement in relieving pain without reducing of sleep disturbances, fatigue, or the poor quality of life with the use of duloxetine and milnacipran than placebo in patients with fibromyalgia. More patients experienced adverse events like as nausea, dry mouth, constipation, headache, somnolence, dizziness and insomnia leading to stopping medications. Whereas, the evidence from clinical studies shows that combined use of pregabalin and SNRIs such as duloxetine has potential efficacy and better tolerability during the treatment of improvement of pain, fatigue, and sleep disorders in patients with fibromyalgia.

The use of the second-generation antidepressants like as paroxetine (a selective serotonin reuptake inhibitors (SSRIs)) and venlafaxine (SNRIs) may be associated with more tolerability and reduce pain in patients with major depressive disorder.

To the best of the investigator's knowledge, the comparison of the long-term efficacy, tolerability, and safety of the combined use of pregabalin with one of the three antidepressants, namely, amitriptyline, venlafaxine, or paroxetine for the treatment of fibromyalgia has not yet been studied.

The investigators hypothesized that the combined use of pregabalin and paroxetine would be associated with comparable Somatic Symptoms Scale-8 (SSS-8) and Center for Epidemiological Studies Depression scales (CESD) and higher tolerability than the use of pregabalin with either amitriptyline or venlafaxine.

Inclusion Criteria:

• Fibromyalgia
• Receiving pregabalin daily

Exclusion Criteria:

• Pathologies mimicking the symptoms of fibromyalgia
• Acute systemic inflammatory diseases
• Infections
• Pregnancy
• Lactating