In an adult with acute neck stiffness and no contraindications, what is the appropriate first‑line pharmacologic treatment (e.g., aceclofenac [Zerodol MR] and/or chlorzoxazone [Myospas])?

First-Line Pharmacologic Treatment for Acute Neck Stiffness

For acute neck stiffness, start with an oral NSAID (such as aceclofenac/Zerodol MR 100 mg twice daily) as first-line therapy, and add a muscle relaxant (chlorzoxazone/Myospas 500 mg twice daily) for short-term use (7-14 days maximum) if muscle spasm is present. 1, 2, 3

Evidence-Based Treatment Algorithm

Step 1: Initial NSAID Therapy

• Oral NSAIDs are the first-line pharmacologic treatment for acute neck pain, with moderate-certainty evidence showing pain reduction at less than 2 hours and at 1-7 days compared to placebo 1
• Aceclofenac (Zerodol MR) 100 mg twice daily is at least as effective as other NSAIDs for reducing pain in musculoskeletal disorders and has a favorable gastrointestinal safety profile 4
• NSAIDs should be prescribed at the lowest effective dose for the shortest necessary duration, with cardiovascular, gastrointestinal, and renal risks assessed before prescribing 1

Step 2: Add Muscle Relaxant if Muscle Spasm Present

• Muscle relaxants are effective for acute neck pain associated with muscle spasm, with evidence supporting their use in the acute setting 2, 3
• Chlorzoxazone (Myospas) 500 mg twice daily is indicated as an adjunct to rest and physical therapy for acute, painful musculoskeletal conditions, though it does not directly relax skeletal muscles and likely works through sedative properties 5
• Limit muscle relaxant use to 7-14 days maximum for acute pain, as all trials were ≤2 weeks duration and there is no evidence supporting longer-term use 1, 6

Step 3: Combination Therapy Considerations

• Combining aceclofenac with chlorzoxazone provides clinically better improvement than triple-drug combinations (chlorzoxazone + aceclofenac + paracetamol), with a statistically significant better safety profile 7
• Low-certainty evidence shows that acetaminophen plus chlorzoxazone reduced pain at 1-7 days (WMD -2.92 cm on 10-cm VAS) compared to placebo 1

Critical Safety Warnings

NSAID Precautions

• Monitor for gastrointestinal adverse events, as moderate-certainty evidence shows oral NSAIDs increase GI risk (OR 1.77) compared to placebo 1
• Assess cardiovascular risk factors before prescribing, as NSAIDs increase cardiovascular risk with longer use and higher doses 6
• Consider co-prescribing a proton pump inhibitor in patients with increased gastrointestinal risk 8

Muscle Relaxant Precautions

• All skeletal muscle relaxants increase CNS adverse events 2-fold (RR 2.04), primarily sedation, drowsiness, and dizziness 1, 9
• Chlorzoxazone requires monitoring for potential hepatotoxicity, which is generally reversible 6, 9
• Avoid muscle relaxants in elderly patients due to high risk of sedation, confusion, and falls 8, 9

Medications to Avoid

• Do not use benzodiazepines (e.g., diazepam) for neck pain, as they have no proven benefit for musculoskeletal pain and carry high risks of abuse and falls 9
• Avoid opioids for acute neck pain, as their efficacy is questionable and they are associated with considerable adverse effects and risk of dependency 1
• Do not use oral ergot alkaloids, as they are poorly effective and potentially toxic 1

When to Reassess

• Evaluate treatment response at 2-4 days for acute pain relief 9
• If insufficient response after 7-14 days of combination therapy, reassess diagnosis and consider alternative causes such as cervical radiculopathy, facet arthropathy, or serious pathology requiring imaging 2, 3
• Red flags requiring immediate evaluation include focal neurologic symptoms, neck stiffness with fever (meningitis), severe headache (subarachnoid hemorrhage), or trauma history 1