What muscle relaxers are safe to use during pregnancy?

Safety of Muscle Relaxants During Pregnancy

Most muscle relaxants should be avoided during pregnancy due to insufficient safety data, with metoprolol being the safest option for muscle cramps when non-pharmacological approaches fail.

First-Line Management: Non-Pharmacological Approaches

Before considering any medication during pregnancy, non-pharmacological approaches should be prioritized:

• Regular stretching of calf muscles before bedtime and throughout the day 1
• Maintaining adequate hydration 1
• Engaging in at least 150 minutes of moderate-intensity physical activity weekly 1
• Oral magnesium supplementation (300 mg daily) which can significantly reduce frequency and intensity of muscle cramps 1

Pharmacological Options

Safe Options

• Beta-1 selective blockers: Metoprolol is preferred for muscle cramps during pregnancy when medication is necessary 2
  • Metoprolol has a lower incidence of fetal growth retardation compared to atenolol 2
  • Beta-1 selective agents are preferred because they avoid beta-2 effects on uterine relaxation 2

Medications to Avoid

1. Cyclobenzaprine: Recent data shows potential associations with birth defects including:

   • Cleft palate (OR = 4.79)
   • Anorectal atresia/stenosis (OR = 6.91)
   • D-transposition of great arteries (OR = 6.97)
   • Coarctation of aorta (OR = 5.58)
   • Pulmonary valve stenosis (OR = 4.55) 3

2. Metaxalone: Should not be used in women who are or may become pregnant, particularly during early pregnancy, unless potential benefits outweigh possible hazards 4

3. Muscle relaxants specifically contraindicated during pregnancy:

   • Atracurium and mivacurium 2
   • Propranolol 2
   • Procainamide 2
   • Quinidine 2
   • Sotalol 2

Special Considerations

Timing During Pregnancy

• All muscle relaxants should be avoided if possible within the first trimester 2
• If absolutely necessary, beta-1 selective blockers may be used with caution after the first trimester 2

Monitoring

• When using beta blockers, monitor for:
  • Fetal bradycardia
  • Potential effects on fetal growth 2
  • Hypoglycemia in the neonate 2

Perioperative Considerations

If a pregnant woman requires surgery:

• Rocuronium and vecuronium are considered safer alternatives to atracurium and mivacurium 2
• Multidisciplinary management is recommended with involvement of surgical, anesthesia, and perioperative medical teams 2

When to Seek Medical Attention

Pregnant women should consult healthcare providers if experiencing:

• Persistent or severe muscle cramps unresponsive to non-pharmacological measures
• Excessive shortness of breath
• Severe chest pain
• Regular and painful uterine contractions
• Vaginal bleeding 1

Algorithm for Management

1. Start with non-pharmacological approaches (stretching, hydration, magnesium supplementation)
2. If symptoms persist and significantly affect quality of life:
   • Consider metoprolol (lowest effective dose)
   • Avoid all other muscle relaxants unless absolutely necessary
3. If medication is required for surgical procedures:
   • Use rocuronium or vecuronium if muscle relaxation is needed
   • Avoid atracurium, mivacurium, and succinylcholine

Remember that the risk-benefit assessment must always prioritize maternal and fetal safety, with the understanding that most muscle relaxants have limited safety data in pregnancy.