Diphenhydramine Dosing for Itching After Cesarean Section
For itching after cesarean section, administer diphenhydramine 25-50 mg orally or intravenously every 6 hours as needed, though nalbuphine 10 mg intramuscularly is significantly more effective than diphenhydramine for preventing and treating neuraxial opioid-induced pruritus. 1, 2
Standard Antihistamine Dosing
- Diphenhydramine 25 mg orally or intravenously every 6 hours as needed is the recommended dose for managing pruritus in the postoperative setting 1
- The FDA-approved dosing allows administration every 4-6 hours with a maximum of 6 doses in 24 hours 3
- For parenteral administration, the standard adult dose is 25-50 mg per dose, with onset of action within several minutes and duration of 4-6 hours 1, 4
Critical Evidence: Diphenhydramine Has Limited Efficacy
The most important clinical consideration is that diphenhydramine is relatively ineffective for neuraxial opioid-induced pruritus after cesarean section. 2, 5
- A randomized trial comparing prophylactic intramuscular diphenhydramine 30 mg versus nalbuphine 10 mg after cesarean delivery with epidural morphine showed pruritus occurred in 68% of the diphenhydramine group versus only 44% in the nalbuphine group (p=0.027) 2
- At 4 and 12 hours postoperatively, pruritus severity was significantly less with nalbuphine than diphenhydramine (p=0.013 and p=0.012 respectively) 2
- Another study found diphenhydramine 30 mg IV had an 80% incidence of pruritus compared to 85% with placebo, demonstrating minimal benefit 5
Recommended Treatment Algorithm
First-Line Approach
- Nalbuphine 10 mg intramuscularly is the most effective option for both prevention and treatment of neuraxial opioid-induced pruritus 2
- This can be administered prophylactically after delivery or as treatment when itching develops 2
Second-Line Approach (if nalbuphine unavailable)
- Diphenhydramine 25-50 mg orally or IV every 6 hours as needed 1
- Alternatively, hydroxyzine 10 mg orally every 6 hours as needed 1
Alternative Consideration
- Ondansetron 0.1 mg/kg IV prophylactically reduced pruritus incidence to 25% compared to 80% with diphenhydramine in one study 5
- However, other research showed ondansetron ineffective when combined with intrathecal morphine and fentanyl 6
Important Clinical Pitfalls
- Do not rely solely on diphenhydramine for neuraxial opioid-induced pruritus, as it provides minimal benefit over placebo 2, 5
- Diphenhydramine causes sedation, which may interfere with early ambulation and breastfeeding 1, 4
- Common adverse effects include hypotension, dizziness, blurred vision, dry mouth, and urinary retention 1
- The sedative effects are potentiated when combined with opioids, which are routinely used postoperatively 1, 4
Context-Specific Considerations
The 2021 PROSPECT guidelines for cesarean section recommend intrathecal morphine 50-100 μg as the cornerstone of analgesia, which commonly causes pruritus 1. While the guidelines do not specifically address antihistamine dosing for pruritus management, the evidence clearly demonstrates that nalbuphine is superior to diphenhydramine for this specific indication 2.