What muscle relaxants are safe for a pregnant patient to use for muscle tension or spasms?

Muscle Relaxants Safe in Pregnancy

Acetaminophen (paracetamol) is the only analgesic with an acceptable safety profile for musculoskeletal pain in pregnancy, while traditional muscle relaxants should be avoided due to limited safety data and potential teratogenic risks. 1, 2

First-Line Approach: Non-Pharmacological Management

Pregnant women should prioritize non-pharmacological interventions over medication for musculoskeletal pain and muscle spasms. 2

• Exercise combined with rest forms the basis for treating chronic musculoskeletal pain in pregnancy, with physical therapy showing rare side effects and no contraindications in pregnant women 2
• Lifestyle modifications including adequate hydration, avoiding sudden position changes, and regular small meals help manage symptoms 1
• The benefits of physical therapy far outweigh risks and provide an accessible way to improve quality of life without fetal exposure 2

Pharmacological Options When Necessary

Acetaminophen (Paracetamol)

Acetaminophen is the preferred and safest medication for musculoskeletal pain management during pregnancy, despite relatively poor efficacy 1, 3

• Remains the recommended first-line pharmacological option throughout all trimesters 1
• Over 60% of pregnant women self-report using analgesics, with acetaminophen being the safest documented option 3

Beta-Blockers for Specific Indications

Beta-1 selective blockers (except atenolol) can be considered for muscle tension related to migraine or tachycardia 1

• Metoprolol (50-100 mg oral twice daily) is preferred over other beta-blockers due to lower incidence of fetal growth retardation compared to atenolol 1, 4
• Propranolol (80-160 mg oral once or twice daily in long-acting formulations) is an alternative option 1
• Atenolol must be avoided due to significant fetal growth restriction 4

Muscle Relaxants to Avoid

Cyclobenzaprine

Cyclobenzaprine shows concerning associations with multiple birth defects and should be avoided 5

• A large case-control study of 33,615 cases found periconceptional cyclobenzaprine exposure associated with increased risk of cleft palate (OR 4.79), anorectal atresia (OR 6.91), d-transposition of great arteries (OR 6.97), and coarctation of aorta (OR 5.58) 5
• Only 0.15% of cases and 0.07% of controls reported use, indicating it is rarely used but carries significant risk when exposure occurs 5

Thiocolchicoside

Thiocolchicoside is contraindicated in pregnancy and lactation 6

• While one small observational study of 18 pregnancies showed no major birth defects, the sample size is insufficient to establish safety 6
• The drug remains contraindicated due to lack of adequate safety data 6

Neuromuscular Blocking Agents

Neuromuscular blockers like rocuronium and vecuronium should only be used in anesthetic settings, never for outpatient muscle spasm management 7, 8

• Atracurium and mivacurium should be avoided even in surgical settings; rocuronium and vecuronium are safer alternatives if neuromuscular blockade is required 7
• Succinylcholine should be avoided 7
• These agents only mask motor manifestations without treating underlying muscle spasm and are inappropriate for non-surgical muscle relaxation 8

Medications Contraindicated Throughout Pregnancy

ACE inhibitors, ARBs, direct renin inhibitors, and mineralocorticoid receptor antagonists are absolutely contraindicated due to fetal toxicity including renal dysplasia, oligohydramnios, growth retardation, and intrauterine death 7, 1

NSAIDs should be avoided in first and third trimesters due to potential fetal risks, though cautious second-trimester use may be considered if absolutely necessary 1

Critical Clinical Pitfalls

• Never prescribe traditional muscle relaxants like cyclobenzaprine, carisoprodol, or methocarbamol as pregnancy safety data is inadequate or shows concerning signals 5
• Over 50% of analgesics are pregnancy category C, and even more are category D specifically in the third trimester 3
• Pharmacokinetic changes in pregnancy (increased renal filtration, cardiac output changes, decreased plasma protein concentration, increased plasma volume) affect drug disposition, but for most muscle relaxants, good prospective clinical trials documenting these changes do not exist 3
• The majority of muscle relaxants lack adequate safety data in pregnancy, making risk-benefit assessment impossible 9, 3

Practical Algorithm

1. Start with non-pharmacological interventions: physical therapy, exercise, rest, hydration 2
2. If medication needed: acetaminophen as first-line pharmacological option 1
3. If acetaminophen insufficient and migraine-related: consider metoprolol (avoid atenolol) 1, 4
4. Avoid all traditional muscle relaxants (cyclobenzaprine, thiocolchicoside, carisoprodol, methocarbamol) 5, 6
5. Multidisciplinary consultation with high-risk obstetrics if symptoms are refractory 1