Management of Postoperative Pruritus from Spinal Morphine
Start with antihistamines (diphenhydramine 25-50 mg IV/PO every 6 hours or promethazine 12.5-25 mg PO every 6 hours) as first-line therapy, and if this fails, use nalbuphine 2.5-5 mg IV as the most effective second-line treatment. 1, 2, 3, 4
First-Line Treatment: Antihistamines
- Begin with diphenhydramine 25-50 mg IV or PO every 6 hours, or promethazine 12.5-25 mg PO every 6 hours. 1, 2, 3
- Antihistamines are recommended as initial therapy by multiple guidelines despite limited mechanistic rationale, since opioid-induced pruritus is primarily mediated through central mu-opioid receptors rather than histamine release. 2
- The incidence of pruritus with neuraxial (spinal) opioids is extremely high—affecting 20-100% of patients—which explains why your patient developed this complication. 1, 2
Second-Line Treatment: Nalbuphine (Most Effective)
- If antihistamines fail, use nalbuphine 2.5-5 mg IV, which is superior to antihistamines, diphenhydramine, naloxone, and propofol for treating opioid-induced pruritus. 3, 4, 5
- Nalbuphine is a mixed agonist-antagonist that works through kappa-opioid receptor activation, which directly counteracts mu-opioid receptor-mediated pruritus. 2, 4, 6
- Critical advantage: Nalbuphine at these low doses (25-50% of analgesic dosing) does not attenuate analgesia and may actually reduce nausea/vomiting. 4
- This makes nalbuphine the ideal choice since your patient needs continued pain control from the spinal morphine. 4
Treatments to AVOID
- Do NOT use ondansetron as first-line therapy. The British Association of Dermatologists explicitly states that ondansetron and other 5-HT3 antagonists do not reduce the incidence or time to onset of opioid-induced pruritus compared to placebo. 1, 2, 5
- While older case reports suggested ondansetron might work, more recent systematic reviews have refuted this. 1, 7, 8
- Prophylactic ondansetron is ineffective for preventing pruritus, though it may have limited utility for treating established pruritus in some patients. 8, 5
Alternative Options if Nalbuphine Unavailable
- Low-dose naloxone infusion: Start at 0.25 mcg/kg/h IV, titrating carefully to avoid reversing analgesia. 3, 5
- Oral naltrexone: 6-9 mg orally (lower doses like 3 mg are ineffective). 5
- IV droperidol: 2.5 mg IV (but not epidural route). 5
Critical Pitfalls to Avoid
- Never give full doses of opioid antagonists without careful titration—this will reverse analgesia and cause significant pain. 1, 2, 3
- Be aware that sedating antihistamines will compound CNS depression from opioids and tramadol, requiring close monitoring. 3
- Pruritus typically occurs early in opioid treatment, so assess for other causes if symptoms persist beyond one week. 2, 3