From the FDA Drug Label
Dosage must be individualized
The FDA drug label does not answer the question.
From the Research
Phenergan (promethazine) is typically administered every 4-6 hours as needed for symptoms such as nausea, vomiting, allergic reactions, or as a sedative. The standard adult dosage ranges from 12.5 mg to 25 mg per dose, with a maximum daily dose of 100 mg, as seen in studies such as 1 where patients received oral promethazine 12.5 mg. For children, dosing is weight-based and should be determined by a healthcare provider, considering the potential for adverse effects as noted in 2 and 3. Phenergan works by blocking histamine H1 receptors and has anticholinergic properties, which helps reduce nausea signals in the brain and provides sedative effects. The medication begins working within 20 minutes when taken orally and its effects can last 4-6 hours, which determines its dosing frequency, as implied by the need for repeated doses in studies like 1 and 4. Some key points to consider when administering Phenergan include:
- The potential for sedation, as noted in 1 where promethazine was associated with sedative side effects
- The need for careful dosing in pediatric patients, as highlighted by the adverse effects observed in 2 and 3
- The importance of monitoring for adverse effects, such as respiratory depression, as seen in 3
- The interaction with other medications, which may affect the dosing frequency and potential for adverse effects Patients should be aware that Phenergan can cause drowsiness, dry mouth, and blurred vision, so activities requiring alertness should be avoided while taking it. The frequency may need adjustment based on individual response, kidney or liver function, age, and concurrent medications, so follow your healthcare provider's specific instructions for your situation. In terms of specific dosing regimens, a study like 1 suggests that oral promethazine 12.5 mg every 12 hours could be effective for preventing postoperative nausea and vomiting, but this should be tailored to the individual patient's needs and response to the medication.