From the FDA Drug Label
DOSAGE AND ADMINISTRATION Promethazine Hydrochloride Tablets USP ... Allergy The average oral dose is 25 mg taken before retiring; however, 12.5 mg may be taken before meals and on retiring, if necessary. Single 25-mg doses at bedtime or 6.25 to 12. 5 mg taken three times daily will usually suffice. Motion Sickness The average adult dose is 25 mg taken twice daily Nausea and Vomiting ... 12.5- to 25-mg doses may be repeated, as necessary, at 4- to 6-hour intervals. Sedation ... Administration of 12. 5 to 25 mg promethazine hydrochloride by the oral route or by rectal suppository at bedtime will provide sedation in children. Adults usually require 25 to 50 mg for nighttime, presurgical, or obstetrical sedation.
The oral Phenergan dose is:
- Allergy: 25 mg taken before retiring, or 12.5 mg before meals and on retiring, or 6.25 to 12.5 mg three times daily
- Motion Sickness: 25 mg twice daily
- Nausea and Vomiting: 12.5 to 25 mg, repeated at 4- to 6-hour intervals as necessary
- Sedation: 12.5 to 25 mg at bedtime for children, and 25 to 50 mg for adults 1
From the Research
Promethazine (Phenergan) is typically prescribed at a dose of 12.5 to 25 mg orally every 4 to 6 hours as needed for adults, with a maximum daily dose not exceeding 100 mg, as supported by the most recent evidence 2. The dosage for children is usually 0.25 to 0.5 mg per kg of body weight every 4 to 6 hours, not to exceed the adult dose.
- When using Phenergan for nausea and vomiting, it's best taken at the first sign of symptoms.
- For sedation or as a sleep aid, it's typically taken 30 minutes before bedtime. Phenergan works by blocking histamine H1 receptors and has anticholinergic properties, which helps reduce nausea and induce sedation.
- Common side effects include drowsiness, dry mouth, and blurred vision.
- Elderly patients and those with certain medical conditions like respiratory problems, glaucoma, or urinary retention should use lower doses.
- Phenergan should not be used in children under 2 years due to the risk of respiratory depression, and caution is advised when driving or operating machinery due to its sedative effects, as noted in various studies 3, 4, 5. Some studies have compared the effectiveness of promethazine with other antiemetic agents, such as ondansetron, in the treatment of nausea and vomiting, with results indicating that promethazine may be more effective in certain cases 5. However, the choice of antiemetic agent depends on various factors, including the patient's medical history, the severity of symptoms, and the potential for side effects. Overall, promethazine remains a commonly used and effective treatment option for nausea and vomiting, with a recommended oral dose and frequency as stated above.