What is the recommended dosing of Promethazine (Phenegran) for pregnant women?

From the Guidelines

Promethazine (Phenegran) should be prescribed at 12.5-25 mg orally every 4-6 hours as needed for nausea and vomiting during pregnancy, with a maximum daily dose of 100 mg, as it is considered a safe and effective option, although it should be used with caution, especially in the first trimester, due to its potential risks 1. The medication works by blocking histamine H1 receptors and has anticholinergic properties that help reduce nausea signals in the brain.

• Key considerations for its use include:
  • Starting dose: 12.5-25 mg orally every 4-6 hours as needed
  • Maximum daily dose: 100 mg
  • Potential side effects: drowsiness, dry mouth, and constipation
  • Recommendation to take the first dose when the patient can rest to assess how drowsy it makes them
  • Importance of medical supervision, especially during pregnancy, and informing the healthcare provider of all other medications being taken to avoid potential interactions. According to the American College of Obstetricians and Gynecologists (ACOG), doxylamine and pyridoxine are recommended as first-line pharmacologic antiemetic therapies for persistent nausea and vomiting of pregnancy (NVP) refractory to non-pharmacologic therapy 1.
• However, promethazine is also considered a safe and effective option, although it should be used with caution, especially in the first trimester, due to its potential risks. Some studies have reported that promethazine has similar efficacy to metoclopramide in patients hospitalized for hyperemesis gravidarum (HG), although it may have a higher risk of adverse events such as drowsiness, dizziness, and dystonia 1.
• Therefore, the decision to use promethazine should be made on a case-by-case basis, taking into account the individual patient's symptoms, medical history, and potential risks and benefits.

From the Research

Recommended Dosing of Promethazine (Phenegran) for Pregnant Women

• The recommended dosing of Promethazine (Phenegran) for pregnant women is not explicitly stated in the provided studies.
• However, according to the study 2, promethazine was compared with metoclopramide in a single study with 146 participants, and more women taking promethazine reported drowsiness, dizziness, and dystonia.
• Another study 3 found that promethazine was associated with greater benefit than placebo for moderate symptoms of nausea and emesis of pregnancy.
• The study 4 mentions that H1 blockers, which include promethazine, have large studies documenting fetal safety.
• The study 5 states that metoclopramide and antihistamines, such as promethazine, are first-line options for nausea and vomiting in pregnancy.

Safety Considerations

• The study 4 highlights the importance of considering fetal safety when using medications to treat nausea and vomiting in pregnancy.
• While promethazine is considered safe for use in pregnancy, the study 2 notes that it can cause drowsiness, dizziness, and dystonia in some women.
• The study 3 also mentions that the quality of evidence for the use of promethazine in pregnancy is low, and more studies are needed to fully understand its safety and efficacy.

Comparison with Other Antiemetics

• The study 2 compares promethazine with other antiemetics, such as metoclopramide and ondansetron, and finds that there is no clear difference in efficacy between them.
• The study 3 also compares promethazine with other antiemetics and finds that it is associated with greater benefit than placebo for moderate symptoms of nausea and emesis of pregnancy.
• The study 5 notes that metoclopramide and antihistamines, such as promethazine, are first-line options for nausea and vomiting in pregnancy, while serotonin antagonists and neurokinin antagonists are more effective for chemotherapy-induced nausea and vomiting.