Dextromethorphan in Fibromyalgia

Fibromyalgia (FM) is a chronic, widespread pain syndrome. Individuals with FM frequently
report body pain, fatigue, sleep issues, cognitive impairment, headaches, and other symptoms.
The disease affects approximately 5% of women in the United States. Many of those patients
suffer with decreased quality of life and loss of employment.

The precise pathological mechanism of FM is not yet understood, and there is no targeted
treatment for the condition. One hypothesis of FM with prior scientific support is that pain
is caused by abnormal inflammation of the brain. When microglia cells in the brain adopt an
inflammatory state, they release chemicals that can cause neurons to increase the
transmission of pain signals.

DXM has been used in previous research and demonstrated to suppress pain symptoms. When given
at higher dosages (above 200mg), the medication acts as a dissociative agent. This dosage can
reduce pain, but produces side-effects that can limit daily functioning. At lower dosages,
however, DXM may reduce inflammatory aspects of chronic pain while not causing dissociative
side effects.

In animal models, central inflammation can be reduced with intraperitoneal dosages of DXM of
0.1mg/kg. In an average U.S. woman, this dosage would translate to approximately 8mg. Because
an oral versus intraperitoneal dosing route will be used, the dose will be raised to 10mg,
administered twice a day (once in the morning and once at night). The investigator will
examine the impact of 20mg total daily DXM on self-reported FM pain.

Inclusion Criteria:

1. Severe chronic fatigue ≥6 consecutive months not due to ongoing exertion or other
medical condition associated with fatigue;

2. Daily self-reported pain of at least 4 out of 10;

3. Meets American College of Rheumatology 2016 case definition criteria for FM;

4. Able to attend UAB for all scheduled appointments;

5. Can complete daily self-reports of pain and other symptoms for duration of project.

Exclusion Criteria:

1. Blood draw contraindicated or otherwise not able to be performed;

2. High-sensitivity C-reactive protein (HS-CRP) ≥ 10 mg/L;

3. Erythrocyte sedimentation rate (ESR) >60 mm/hr;

4. Positive rheumatoid factor;

5. Positive anti-nuclear antibody (ANA);

6. Abnormal thyroid stimulating hormone or free thyroxine;

7. Diagnosed rheumatologic or auto-immune condition;

8. Blood or clotting disorder;

9. Use of blood thinning medication;

10. Current use of MAOI

11. Daily consumption of grapefruit juice

12. Oral temperature >100˚F at baseline;

13. Febrile illness or use of antibiotics in the 4 weeks before study commencement;

14. Planned surgery or procedures during the study period, or operated on in the 4 weeks
before study commencement;

15. Pregnant or planning on becoming pregnant within 6 months, or currently breastfeeding

16. Regular use of any anti-inflammatory medication (such as aspirin, ibuprofen,
naproxen);

17. Baseline HADS (Hospital Anxiety and Depression Scale) depression subscale score of
≥16;

18. Current litigation or worker's compensation claim;

19. Current participation in another treatment trial;

20. Planned vaccination during the study period, or vaccinated in the 4 weeks before study
commencement.