Medications For Low Back Pain
Low back pain (LBP) is one of the most common complaints encountered by primary care practitioners. LBP, which may radiate from the back into the lower extremities, hips, and buttocks, is considered acute if it lasts 6 weeks or less and chronic if it lasts longer than 12 weeks.
A thorough assessment of the underlying etiology, including a complete history and physical examination, is necessary to correctly identify the underlying pain trigger. Understanding the potential etiologies, such as inflammatory, biomechanical, infectious, neoplastic, and/or psychological processes, will help guide the treatment plan. This allows clinicians to use the appropriate class(es) of medications advantageously.
Nonsteroidal anti-inflammatory drugs (NSAIDs) are the world’s most frequently prescribed medications.1,2 In 2000, the US Medical Expectations Panel Survey found that of the 44 million prescriptions written for the 24.5 million patients with both acute and chronic LBP, 16.3% were for nonselective NSAIDs and 10% were for selective cyclooxygenase (COX)-2 inhibitors.3
NSAIDs are a class of medications that cause a reversible blockade of COX isoenzymes; they block the inflammatory process in which arachidonic acid is converted into the prostaglandins that mediate inflammation and sensitize peripheral nociceptors. This is the means by which this class of medications exerts both anti-inflammatory and analgesic effects.4-6 NSAIDs also affect inflammation locally by inhibiting neutrophil function and phospholipase C activity.
NSAIDs can further be divided into two groups consisting of older, nonselective NSAIDs that inhibit both COX-1 and COX-2 enzymes, and newer COX-2 selective NSAIDs that block only the COX-2 isoenzyme. The only COX-2 selective inhibitor currently on the market is celecoxib (Celebrex); rofecoxib (Vioxx) and valdecoxib (Bextra) were voluntarily withdrawn from the market because of cardiovascular safety concerns. There are various subtypes of NSAIDs, each with various properties and side-effect profiles (Table 1).
Most over-the-counter (OTC) NSAIDs are fairly inexpensive. However, the consideration of cost should also include the cost of side effects. In a Canadian study on the cost of NSAID-related gastrointestinal (GI) side effects in elderly patients, Rahme et al found that for each $1 spent on nonselective NSAIDS, an extra $0.66 was spent on treating adverse events (AEs).7
A more recent article looked into both GI and cardiovascular AEs and compared three groups of medications: nonselective NSAIDs, NSAID plus proton pump inhibitor (PPI) combination therapy, and COX-2 selective agents. The investigators found that nonselective NSAIDs were most cost-effective in low-risk patients, whereas NSAID plus PPI combination therapy was more cost-effective for preventing ulcers in patients taking aspirin or otherwise at high risk for a GI or cardiovascular AE.8
Contraindications for NSAIDs include peptic ulcer disease, bleeding disorders, and allergic reactions to NSAIDs. Additionally, patients with congestive heart failure and renal disease should be monitored closely and perhaps not prescribed NSAIDs.9 Nonselective NSAIDs are contraindicated in the last trimester of pregnancy, during the perioperative period for cardiac surgery, and in patients who are at high risk for bleeding.5 Celecoxib is contraindicated in patients with sulfonamide hypersensitivity and should be used with caution in those with cardiac disease and hypertension.10
With respect to efficacy, one systematic review found that NSAIDs were effective for short-term relief of chronic LBP.11 Of the randomized controlled trials (RCTs) used for European guidelines, the only “high-quality” (30-patient) trial showed better pain relief with diflunisal than with placebo.1,12 In a more recent Cochrane systematic review of 65 studies that compared NSAIDs with placebo, the authors concluded that NSAIDs are slightly more effective than placebo at providing short-term pain relief in patients with LBP without radiating symptoms.13 In patients with radiating lower extremity symptoms, NSAIDs were no more effective than placebo. In addition, this review found that COX-2 selective NSAIDs were not more effective than nonselective NSAIDs, but caused fewer side effects, especially gastric ulcers. However, the authors acknowledge that COX-2 inhibitors present cardiovascular risks for some patients. The authors also found that NSAIDs are equally as effective as other medications (eg, paracetamol/acetaminophen, narcotic analgesics, and muscle relaxants). However, this review conceded that fewer than half of the studies were high quality, many had small patient numbers, and few contained data on long-term results and side effects.
Based on recent evidence regarding the efficacy of NSAIDs, these agents are best used in standard daily doses over a short time frame (<2 weeks) in patients with LBP without associated radiculopathy who do not have contraindications; however, they are not indicated for long-term treatment of LBP. Although COX-2 selective NSAIDs have fewer side effects than nonselective NSAIDs, it is well documented that they present cardiovascular risks for some patients.
Muscle relaxants are a group of medications used as adjunctive treatment of mild to severe acute LBP (Table 2). These medications work by inhibiting central polysynaptic neuronal events that act indirectly on skeletal muscle.5 They can be subdivided into antispasmodic and antispastic medications.14
Antispasmodic muscle relaxants can be further subdivided into benzodiazepines and nonbenzodiazepines. Benzodiazepine antispasmodic medications, such as alprazolam, clonazepam, dalmane (Flurazepam), diazepam, and hydroxyzine act as skeletal muscle relaxants, sedatives, hypnotics, anticonvulsants, and anxiolytics. It is important to note that patients often develop tolerance to their muscle relaxant effects. Because of potential for abuse, these agents should be used cautiously in patients with a history of addiction.
Nonbenzodiazepines, which act centrally at the brain or spinal cord level to decrease muscle spasms, include medications such as cyclobenzaprine and tizanadine. Tizanadine acts as an α2-adrenergic agonist to inhibit presynaptic motor neurons. Cyclobenzaprine works at the brain- stem level, whereas metaxalone works via generalized central nervous system (CNS) depression.5,6