Can muscle relaxers affect gastric emptying?

Impact of Muscle Relaxants on Gastric Emptying

Yes, muscle relaxants can significantly delay gastric emptying, particularly opioid analgesics, which should be avoided in patients with gastroparesis due to their negative effects on gastric motility.

Mechanism of Action and Effects on Gastric Motility

Muscle relaxants can affect gastric emptying through several mechanisms:

1. Anticholinergic Effects:

   • Many muscle relaxants have anticholinergic properties that directly oppose the action of acetylcholine
   • Metoclopramide, a prokinetic agent, works by sensitizing tissues to acetylcholine, increasing gastric motility 1
   • Muscle relaxants with anticholinergic properties can counteract this mechanism, slowing gastric emptying

2. Central Nervous System Effects:

   • Skeletal muscle relaxants often cause sedation through central mechanisms 2
   • This sedative effect can indirectly slow gastrointestinal motility

3. Specific Agents and Their Effects:

   • Opioid analgesics: These significantly delay gastric emptying and should not be used to manage chronic visceral abdominal pain as they "further delay gastric emptying, increase the risk of narcotic bowel syndrome, and create the potential for addiction, tolerance, and overdose" 3
   • Tricyclic antidepressants: Medications like amitriptyline have been shown to slow gastric emptying of solids in healthy volunteers 4

Clinical Implications

For Patients with Gastroparesis:

• Avoid medications that delay gastric emptying when treating patients with gastroparesis or delayed gastric emptying
• The AGA Clinical Practice Update specifically warns against opioid use in gastroparesis patients 3
• For patients requiring muscle relaxation who also have gastroparesis, consider agents with minimal anticholinergic effects

For Anesthesia Practice:

• In patients requiring rapid sequence induction to prevent aspiration of gastric contents, muscle relaxants are actually recommended to facilitate quick and proper tracheal intubation 3
• Suxamethonium and rocuronium are preferred in this setting due to their rapid onset 3

Alternative Approaches for Pain Management

For patients with gastroparesis who require pain management:

• First-line options: Non-pharmacologic approaches including exercise, multidisciplinary rehabilitation, and cognitive behavioral therapy 5

• For neuropathic/visceral pain:

  • SNRIs like duloxetine (60-120 mg/day)
  • Gabapentin (>1200 mg/day in divided doses)
  • Pregabalin (100-300 mg/day in divided doses) 3, 5

• For nausea and vomiting:

  • 5-HT3 antagonists (ondansetron, granisetron)
  • NK-1 receptor antagonists (aprepitant)
  • Prokinetic agents that accelerate gastric emptying (metoclopramide, erythromycin) 3, 6

Monitoring Recommendations

When muscle relaxants must be used in patients with gastroparesis or at risk for delayed gastric emptying:

• Monitor for worsening of gastroparesis symptoms
• Consider prokinetic therapy to counteract the effects on gastric emptying
• Assess for drug interactions, particularly between prokinetics and muscle relaxants

Conclusion

Muscle relaxants, particularly those with anticholinergic properties and opioids, can significantly delay gastric emptying. This effect should be carefully considered when prescribing these medications to patients with existing gastroparesis or those at risk for aspiration.