Efficacy and Safety of Pregabalin/Tizanidine vs. Pregabalin in Patients With Fibromyalgia

The primary outcome is change from baseline to 12 weeks of treatment in average pain intensity during the last 7 days on an 11-point rating scale (ranging from 0 = "no pain" to 10 = "unbearable pain") using the first item from the symptom part of the Fibromyalgia Impact Questionnaire Revised (FIQR)

The FIQR is a well-validated multidimensional instrument that measures participant-rated overall severity of fibromyalgia, including intensity of pain, physical function, fatigue, morning tiredness, depression, anxiety, job difficulty, and overall well-being. Each item is standardized on a scale ranging from 0 to 10, with lower scores indicating more improvement or less negative impact. In addition, FIQR is also assessed weekly during the intervention period for all groups of participants as well as at the 24-week time points as secondary outcomes.

Health Related Quality of Life assessments are made using the Medical Outcome Study Short Form 36 Health Survey (SF-36). The SF-36 is a self-administered, 36-item questionnaire that assesses the concepts of physical functioning, role limitations due to physical problems, social function, bodily pain, general mental health, role limitations due to emotional problems, vitality, and general health perceptions. Summary scores include physical function, mental function, and combined total function. Scores range from 0 to 100, with higher scores indicating better health status.

The Patient's Global Assessment (Global Visual Analogue Scale) is a visual analogue scale that measures the level of fibromyalgia severity on a 10-point scale with 10 reflecting the most extreme severity and 0 reflecting no severity.

The Beck II Depression Inventory (BDI) is a 21-question, validated, self-report instrument that measures the severity of depressive symptoms (each scored 0-3, sum=0-63). Higher scores reflect a greater degree of symptom severity. The total questionnaire score ranges from 0 to 63 points. The result is interpreted by the usual classifications as follows: no depression (0-9 points), mild depression (10-18 points), moderate depression (19-29 points) and severe depression (>30 points).

The Pittsburgh Sleep Quality Index is an 11-item, validated, self-report questionnaire that measures sleep quality. Lower scores are associated with better sleep quality. This questionnaire has 7 dimensions: subjective quality, sleep latency, sleep duration, habitual sleep efficacy, sleep perturbations, use of hypnotic medication, and daily dysfunction. Each dimension is scored from 0 (no problems) to 3 (severe problems), where the total score varies in a range from 0 to 21 points.

The Hospital Anxiety and Depression Scale is a 14-item, validated, self-report questionnaire that assesses levels of depression and anxiety. Higher scores reflect greater levels of anxiety and depression.

The Perceived Stress Scale is the most widely used psychological instrument for measuring the perception of stress. The 10-item scale also includes a number of direct queries about current levels of experienced stress. For this instrument, higher scores reflect a greater degree of symptom severity.

Pain distribution: assessed by the Widespread Pain Index (WPI) from the 2016 diagnostic criteria for fibromyalgia.

Frequency and severity of AEs, Patient safety will be ensured by vigilant AE assessment and judicious drug titration. Any occurrences of major AEs will be tracked as secondary outcomes and also reported to the Ethics Board. Assessment and reporting of AEs will adhere to Consolidated Standards for Reporting Trials recommendations.