What is the recommended dose of Phenergan (promethazine) for hyperemesis gravidarum?

Promethazine Dosing for Hyperemesis Gravidarum

For hyperemesis gravidarum, promethazine (Phenergan) should be administered at 12.5-25 mg every 4-6 hours as needed, typically as a second-line agent after first-line therapies have failed. 1

Treatment Algorithm for Hyperemesis Gravidarum

First-Line Treatments

1. Non-pharmacological approaches:

   • Small, frequent, bland meals
   • High-protein, low-fat diet
   • Avoiding triggers (strong odors, spicy/fatty foods)
   • Maintaining hydration with small, frequent sips

2. First-line medications 2, 1:

   • Vitamin B6 (pyridoxine) 10-25 mg every 8 hours
   • Doxylamine 10-20 mg at bedtime or every 8 hours
   • Ginger 250 mg capsules 4 times daily

Second-Line Treatments (When First-Line Fails)

1. H1-receptor antagonists 1:

   • Promethazine 12.5-25 mg every 4-6 hours (oral, rectal, or IV)
   • Dimenhydrinate 50-100 mg every 4-6 hours

2. Dopamine antagonists 2, 1:

   • Metoclopramide 10 mg every 6-8 hours
   • Note: Metoclopramide has similar efficacy to promethazine but with fewer side effects like drowsiness, dizziness, and dystonia 2

3. Serotonin antagonists 1:

   • Ondansetron 4-8 mg every 6-8 hours (use with caution in first trimester)

Third-Line Treatments (For Refractory Cases)

1. Corticosteroids 2, 1:

   • Methylprednisolone 16 mg IV every 8 hours for up to 3 days, followed by tapering over 2 weeks
   • Avoid before 10 weeks gestation due to increased risk of oral clefts

2. Other options for resistant cases 3:

   • Mirtazapine 30 mg/day (limited evidence but has shown effectiveness in case reports)

Important Considerations When Using Promethazine

• Monitor for side effects: Drowsiness, dizziness, and extrapyramidal symptoms are common with phenothiazines like promethazine 2
• Discontinue if extrapyramidal symptoms develop 2
• Administration routes: Can be given orally, rectally, or intravenously when oral intake is not tolerated 1
• Combination therapy: Consider using multiple concurrent agents in alternating schedules or routes for severe cases 1
• Routine dosing: Use around-the-clock administration rather than PRN dosing for better symptom control 1

Indications for Hospitalization and IV Therapy

Hospitalization should be considered when 2, 1:

• Dehydration is present
• Weight loss >5% of pre-pregnancy weight
• Electrolyte imbalances are detected
• Outpatient management has failed

For hospitalized patients:

• IV fluid and electrolyte replacement
• IV thiamine supplementation (100 mg daily for minimum 7 days, followed by 50 mg daily until adequate oral intake) 2, 1
• IV antiemetics including promethazine when oral intake is not tolerated

Monitoring and Follow-up

• Monitor weight to ensure no significant loss (>5% of pre-pregnancy weight) 1
• Assess for signs of dehydration, including orthostatic hypotension, decreased skin turgor, and dry mucous membranes 1
• Evaluate severity using the Pregnancy-Unique Quantification of Emesis (PUQE) score 1
• Monitor for potential complications such as Wernicke's encephalopathy and thromboembolism 4, 5

Remember that hyperemesis gravidarum typically begins at 4-6 weeks, peaks at 8-12 weeks, and usually subsides by week 20 of pregnancy 1. Treatment should be continued until symptoms adequately resolve.