Efficacy and safety of skeletal muscle relaxants used long term for chronic pain

Centrally-acting skeletal muscle relaxants include antispasticity and antispasmodic medications, such as baclofen, chlorzoxazone, cyclobenzaprine, methocarbamol, orphenadrine and tizanidine. They are indicated for acute musculoskeletal conditions including spasms and low back pain, and are also used off-label for numerous other pain and nonpain conditions. These agents should be used with caution because of their central nervous system adverse effects, including drowsiness and dizziness, particularly when used in combination with other centrally-acting medications. Due to these adverse effects and lack of evidence for long-term efficacy, recommendations generally limit the use of skeletal muscle relaxants to a maximum duration of two to three weeks. In recent years, stricter guidelines for prescribing opioids have led to an increased number of prescriptions for skeletal muscle relaxants for chronic pain. However, the efficacy of skeletal muscle relaxants used long term for chronic pain is unknown.To address this issue, researchers systematically reviewed the effectiveness of long-term use (≥ 4 weeks) of skeletal muscle relaxants for chronic pain (lasting ≥ 3 months). The review included only randomized clinical trials and cohort studies with comparator groups evaluating at least a one-month duration of skeletal muscle relaxant use for chronic pain. The included studies were classified by chronic pain syndrome: low back pain, fibromyalgia, headaches, painful cramps or spasticity, and other pain syndromes (osteoarthritis, cervical spondylosis, neuropathy, cancer pain, gastric reflux-related pain, orchialgia).The main findings are summarized below:The review included 30 randomized controlled trials with 1,314 participants and 14 cohort studies with 1,168 participants who received skeletal muscle relaxants for chronic pain. The randomized controlled trials had a low to moderate risk of bias, and the quality of cohort studies was fair to good.Studies were primarily short-term (4–6 weeks). Nine different skeletal muscle relaxants were represented in the studies identified. Eleven studies (25%) examined baclofen, eight (18%) examined tizanidine, and seven (16%) examined cyclobenzaprine. Evidence for effectiveness was strongest for skeletal muscle relaxants used for trigeminal neuralgia, neck pain or painful cramps.Evidence suggested that skeletal muscle relaxants were not more beneficial than placebo for the treatment of fibromyalgia, low back pain or other pain syndromes.The most common adverse effects were sedation, dizziness and dry mouth. No studies measured the misuse of skeletal muscle relaxants.The authors conclude that in this systematic review, long-term use of skeletal muscle relaxants for chronic pain may be beneficial for patients with painful spasms or cramps and neck pain. However, long-term use for low back pain, fibromyalgia or headaches did not appear to be beneficial. The authors recommend that clinicians should be vigilant for adverse effects of skeletal muscle relaxants and consider deprescribing these agents if pain-related goals are not met.The authors caution that most studies in their review lasted only a month or slightly longer, and this short duration may bias toward higher efficacy (many pharmacologic treatments for pain show declining efficacy over time) and toward fewer adverse effects (which may develop over time, including misuse of skeletal muscle relaxants).The investigators also point out that previous studies suggest that as many as 30% ofindividuals using opioids are also prescribed skeletal muscle relaxants. Such combinations increase the risk of opioid-related overdose, particularly in those taking skeletal muscle relaxants for longer durations. In addition, despite increasing prevalence of skeletal muscle relaxant use, this systematic review suggests only limited evidence of efficacy for long-term use in a small number of pain syndromes.Reference:Oldfield BJ, Gleeson B, Morford KL, et al. Long-term use of muscle relaxant medications for chronic pain. A systematic review. JAMA Network Open 2024;7(9):e2434835. (accessed September 19, 2024).

Efficacy and safety of skeletal muscle relaxants used long term for chronic pain

Register for free access or login.

Related Topics