Management of Itching After Spinal Anesthesia Due to Intrathecal Opioids
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 treatment, and if this fails, escalate to low-dose nalbuphine (2.5-5 mg IV) or carefully titrated naloxone infusion (0.25 mcg/kg/h), as these are the most effective evidence-based interventions. 1, 2, 3
Understanding the Problem
Pruritus after intrathecal opioids is extremely common and predictable:
- Intrathecal/epidural opioids cause pruritus in 20-100% of patients, making this the highest-risk route of administration 4, 1, 2
- Intravenous opioids cause pruritus in only 10-50% of patients 4, 1
- The itching typically occurs early in the course of opioid treatment 1, 2
- While not life-threatening, it significantly decreases patient satisfaction and comfort 5
Stepwise Treatment Algorithm
First-Line: Antihistamines
- Diphenhydramine 25-50 mg IV or PO every 6 hours (sedating option) 1, 2
- Promethazine 12.5-25 mg PO every 6 hours (sedating option) 1, 2
- Cetirizine may be used as a non-sedating alternative 1
- Important caveat: Sedating antihistamines will compound opioid-induced sedation, requiring close monitoring 1, 2
Second-Line: Mixed Agonist-Antagonist
- Nalbuphine 2.5-5 mg IV (25-50% of the analgesic dose) is superior to placebo, diphenhydramine, naloxone, and propofol for treating opioid-induced pruritus 3, 6
- Nalbuphine provides pruritus relief without attenuating analgesia or increasing sedation when used at these lower doses 3
- Can be dosed as 0.5-1 mg IV every 6 hours as needed 1
- This is the most effective single agent based on systematic review evidence 3, 6
Third-Line: Opioid Antagonists
- Naloxone continuous infusion starting at 0.25 mcg/kg/h, titrated carefully 1, 2
- Naltrexone 6-9 mg is effective but may reduce duration of analgesia 4, 6
- Naltrexone 3 mg is ineffective; 6 mg and 9 mg doses work but with analgesic trade-offs 4, 6
- Critical warning: Careful dose titration is essential to avoid reversing analgesic effects 1, 2, 7
- Methylnaltrexone (peripheral antagonist with reduced CNS penetration) may be considered as an alternative 4, 1
Fourth-Line: Alternative Agents
- Droperidol 2.5 mg IV is efficacious for prophylaxis (not epidural route) 6
- Ondansetron 4-8 mg may reduce severity but does not reduce incidence or time to onset 4, 7, 6
- Mirtazapine or gabapentin as alternative antipruritic agents 1
What Does NOT Work
Avoid these ineffective interventions:
- Ondansetron and other 5-HT3 antagonists do not reduce incidence of opioid-induced pruritus despite efficacy for nausea 4, 7
- Prophylactic propofol (though low-dose propofol for established pruritus was studied, it showed no benefit) 6
- Epidural clonidine, epidural prednisone, intramuscular hydroxyzine 6
Clinical Considerations for Intrathecal Morphine Use
When intrathecal morphine 0.1 mg is used for postoperative analgesia:
- Pruritus occurs more frequently with the 0.1 mg dose compared to 0.05 mg, though pain relief is superior 4
- The PROSPECT guidelines note significant controversy about using intrathecal morphine due to pruritus and nausea potentially delaying ambulation 4
- Before attributing pruritus solely to opioids, assess for other causes including other medications and underlying conditions 1, 7
Common Pitfalls to Avoid
- Do not use full doses of opioid antagonists in opioid-dependent patients as this precipitates withdrawal 7
- Do not rely on ondansetron as first-line despite its efficacy for opioid-induced nausea 7
- Do not overlook the compounding sedation when combining sedating antihistamines with neuraxial opioids 1, 2
- Do not assume all antihistamines are equally effective—evidence specifically supports diphenhydramine and promethazine 1, 2
Prophylaxis Considerations
For prophylaxis in patients receiving neuraxial opioids: