From the Guidelines

Skeletal muscle relaxants are the most effective analgesic for muscle spasm pain.

A higher-quality Cochrane review found skeletal muscle relaxants to be moderately superior to placebo for short-term pain relief in acute low back pain 1.
The relative risks for not achieving pain relief were 0.80 (CI, 0.71 to 0.89) at 2 to 4 days and 0.67 (CI, 0.13 to 3.44) at 5 to 7 days 1.
Tizanidine was found to be efficacious for acute low back pain in 8 trials, while there is only sparse evidence for the efficacy of dantrolene and baclofen for low back pain 1.
Some key points to consider when prescribing skeletal muscle relaxants include:
- They are associated with a higher total number of adverse events (RR, 1.50 [CI, 1.14 to 1.98]) and central nervous system adverse events (RR, 2.04 [CI, 1.23 to 3.37]) compared with placebo 1.
- Most events were self-limited and serious complications were rare 1.

Opioid analgesics may be considered for patients with severe, disabling pain that is not controlled with acetaminophen and NSAIDs, but their use should be carefully weighed due to substantial risks, including aberrant drug-related behaviors with long-term use 1.
NSAIDs are more effective for pain relief than acetaminophen, but are associated with gastrointestinal and renovascular risks, and should be prescribed with caution 1.

From the Research

The most effective analgesic for muscle spasm pain can be determined by examining the results of various studies.

Cyclobenzaprine has been shown to be effective in relieving acute muscle spasm, with once-daily cyclobenzaprine extended release (CER) 15 and 30 mg demonstrating significant improvements in patient-rated medication helpfulness and relief from local pain compared to placebo 2.
Combination therapy with cyclobenzaprine and ibuprofen has also been studied, with results showing that it is not superior to cyclobenzaprine alone in adult patients with acute neck and back pain with muscle spasm 3.
Eperisone hydrochloride in combination with non-steroid anti-inflammatory drugs (NSAIDs) has been shown to be effective in reducing symptoms of patients with acute non-specific back pain with muscle spasm, with clinically significant pain reduction observed in a higher percentage of patients in the experimental group compared to the control group 4.
Skeletal muscle relaxants, including cyclobenzaprine, tizanidine, methocarbamol, and metaxalone, have been found to be effective for short-term relief of acute low back pain when NSAIDs or acetaminophen are not effective or tolerated, although the choice of agent should be based on side-effect profile, patient preference, abuse potential, and possible drug interactions 5.

Comparing the effectiveness of different analgesics for muscle spasm pain:

Cyclobenzaprine has been found to be effective in various musculoskeletal conditions, with sedative properties that may benefit patients with insomnia caused by severe muscle spasms 5.
Eperisone hydrochloride in combination with ibuprofen has been shown to be effective in reducing pain and improving functional outcomes in patients with acute non-specific back pain with muscle spasm, with a similar safety profile to ibuprofen alone 4.
The combination of an SMR and an NSAID or COX-2 inhibitor, or the combination of SMR and tramadol/acetaminophen, has been found to be superior to single agents alone in the treatment of acute, uncomplicated musculoskeletal disorders 6.