Phenergan (Promethazine) Syrup Dosing Calculation
To obtain 25 mg of promethazine from a syrup containing 5 mg per 5 mL, you need to take 25 mL.
Calculation Method
The calculation is straightforward using the concentration provided:
- Concentration: 5 mg promethazine per 5 mL of syrup 1
- Desired dose: 25 mg
- Volume needed: (25 mg ÷ 5 mg) × 5 mL = 25 mL
Standard Adult Dosing Context
This 25 mg dose aligns with standard adult dosing recommendations for promethazine:
- For allergies: The average oral dose is 25 mg taken before bedtime, or 12.5 mg may be taken before meals and at bedtime if necessary 1
- For motion sickness: The average adult dose is 25 mg taken twice daily, with the initial dose taken one-half to one hour before anticipated travel 1
- For nausea and vomiting: The average effective dose for active therapy is 25 mg, which may be repeated as necessary at 4- to 6-hour intervals 1
Important Safety Considerations
- Pediatric contraindication: Promethazine is contraindicated for children under 2 years of age due to risk of fatal respiratory depression 1
- Sedation effects: Promethazine commonly causes drowsiness and sedation, which should be anticipated when planning activities 2
- Anticholinergic effects: The medication may cause dry mouth and has anticholinergic properties that can affect patients with certain conditions 2