Amrix (Cyclobenzaprine hydrochloride Extended release capsules) is approved by the FDA as a muscle relaxant, indicated for the treatment of muscle spasm associated with acute, painful musculoskeletal conditions. Cyclobenzaprine ER (Amrix TM) has a distinct pharmacokinetic profile providing early systemic exposure and consistent plasma concentration over several hours. Overall, a single dose of Amrix 30 mg is similar to that of cyclobenzaprine immediate release 10 mg three times daily. This ER formula should improve compliance, with similar efficacy and possibly less side effects as is often the case with slower release formulations.
There are clinical studies showing that cyclobenzaprine can alleviate pain secondary to Fibromyalgia induced muscle tone. This multi-layered evidence base suggests that cyclobenzaprine may be able to alleviate pain in fibromyalgia. Theoretically in fibromyalgia, pain is interpreted centrally and possibly occurs due to said muscle spasm . Cyclobenzaprine may relieve this pain, thus allowing patients to function better during the day and sleep better at night. Cyclobenzaprine has tricyclic antidepressant structure which may also allow pain signal dampening in the spinal cord as well, similar to amitriptyline which is used off-label for neuropathic pain as well.
Fibromyalgia (FM) is an illness that may involve medical, rheumatologic, autoimmune, sleep, endocrine and psychiatric pathology. It is a syndrome of recurrent pain at trigger points. Greater than 90% of these patients will report fatigue as a key symptom as well. There are several investigation lines into the treatment of FM induced pain. Exercise, behavioral therapy, amitryptiline, duloxetine, tramadol, sodium oxybate, pregabalin all have randomized trials and almost all focus on pain. There are very few studies evaluating cyclobenzaprine and none studying to Cyclobenzaprine ER formulation. None evaluate pain reduction, sleep and fatigue improvement.
Cyclobenzaprine is a drug with minimal adverse effects (dry mouth, dizziness, fatigue, constipation, somnolence, nausea, and dyspepsia). It may have a safer tolerability profile than some of the FM medications noted above. As cyclobenzaprine is often studied and often added as an augmentation agent to patients' regimens who suffer from acute painful musculoskeletal conditions, the authors feel that cyclobenzaprine would also be effective in this population. The authors wish to conduct a study to determine if cyclobenzaprine ER is safe and tolerable in the treatment of FM induced pain, and secondary fatigue and insomnia. This initial study may allow for continued regulatory studies with this product in FM subjects. The authors propose a double-blind placebo controlled study to determine if cyclobenzaprine ER is safe and effective in reversing FM induced pain, and secondary fatigue and insomnia.