Can Pepcid (famotidine) be used to treat itching caused by intrathecal morphine post-operatively?

Famotidine (Pepcid) for Intrathecal Morphine-Induced Pruritus

Famotidine (Pepcid) is not recommended for treating intrathecal morphine-induced pruritus post-operatively, as there is no evidence supporting H2-receptor antagonists for this indication.

Evidence-Based Treatment Options

First-Line: Ondansetron (5-HT3 Antagonist)

Ondansetron 4-8 mg IV is the most effective evidence-based treatment for established intrathecal morphine-induced pruritus, with an 80% treatment success rate compared to 36% with placebo 1. Key considerations:

• For treatment of active pruritus: Administer ondansetron 4-8 mg IV when moderate to severe itching develops 1
• Treatment efficacy: Provides relief within 30 minutes in 80% of patients, with only 12% recurrence within 4 hours 1
• Prophylactic use is NOT recommended: Multiple high-quality studies demonstrate that prophylactic ondansetron does not prevent pruritus from occurring 2, 3
• Additional benefit: Ondansetron simultaneously reduces nausea and vomiting, making it particularly valuable when both symptoms coexist 1

Why Not Antihistamines?

Traditional antihistamines like diphenhydramine are ineffective for intrathecal morphine-induced pruritus 4. In a randomized trial, diphenhydramine 30 mg IV showed no difference from placebo (80% vs 85% incidence) 4. This is because:

• Opioid-induced pruritus is mediated through central opioid receptors and 5-HT3 pathways, not histamine release 5
• H1-antihistamines cause sedation without addressing the underlying mechanism 4
• H2-antagonists like famotidine have no role in this pathway and lack any supporting evidence 5

Alternative Treatments When Ondansetron Fails

If ondansetron is ineffective or contraindicated, consider these evidence-based alternatives from the British Association of Dermatologists guidelines 5:

• Nalbuphine or butorphanol (κ-opioid agonists): Effective but only available as injections, limiting use outside critical care 5
• Droperidol 2.5-5 mg IV: May prevent or treat opioid-induced pruritus 5
• Mirtazapine 30 mg orally: Shown to prevent morphine-induced pruritus in surgical settings 5
• Gabapentin 1200 mg daily (divided doses): Demonstrated prevention of morphine-induced pruritus 5

Prevention Strategy: Dose Optimization

The most effective prevention is using the lowest effective intrathecal morphine dose 5, 6:

• Optimal dose: 0.1 mg (100 μg) provides adequate analgesia for 24 hours with acceptable side effect profile 5, 6
• Higher doses increase pruritus risk: Patients receiving 0.1 mg experienced more pruritus than those receiving 0.05 mg, though with better analgesia 5
• Cesarean delivery: Doses ≤100 μg provide adequate analgesia with reduced side effects 6

Common Pitfalls to Avoid

• Do not use famotidine or other H2-antagonists: No mechanism of action or evidence for opioid-induced pruritus 5
• Avoid prophylactic ondansetron: Multiple studies show it does not prevent pruritus, only treats it once established 2, 3
• Do not use diphenhydramine as first-line: Ineffective and causes unwanted sedation 4
• Remember ondansetron treats but doesn't prevent: Wait for pruritus to develop before administering 3, 1

Clinical Algorithm

1. Prevention: Use intrathecal morphine 0.1 mg (100 μg) or less 5, 6
2. If moderate-severe pruritus develops: Administer ondansetron 4-8 mg IV 1
3. If ondansetron fails: Consider droperidol 2.5-5 mg IV or nalbuphine (if available) 5
4. Avoid: Famotidine, diphenhydramine, or prophylactic 5-HT3 antagonists 5, 2, 4, 3