Promethazine Supply Duration Calculation
A 160 ml supply of promethazine at 5 ml per dose every 4-6 hours will last approximately 5-8 days, depending on dosing frequency.
Dosing Frequency and Duration
The duration of action for promethazine is 4-6 hours after oral administration, with clinical effects lasting generally four to six hours, though they may persist as long as 12 hours 1. This establishes the dosing interval range.
Maximum Frequency Scenario (Every 4 Hours)
- Doses per day: 6 doses (24 hours ÷ 4 hours)
- Daily volume: 30 ml (5 ml × 6 doses)
- Supply duration: 5.3 days (160 ml ÷ 30 ml/day)
Minimum Frequency Scenario (Every 6 Hours)
- Doses per day: 4 doses (24 hours ÷ 6 hours)
- Daily volume: 20 ml (5 ml × 4 doses)
- Supply duration: 8 days (160 ml ÷ 20 ml/day)
Clinical Context
Promethazine is commonly prescribed at 12.5-25 mg every 4-6 hours for breakthrough antiemetic treatment 2, 3. The 5 ml dose likely corresponds to a standard concentration (typically 6.25 mg/5 ml or 5 mg/5 ml depending on formulation).
The practical answer is that this prescription will last between 5 and 8 days, with the actual duration determined by how frequently the patient needs to take the medication within the prescribed 4-6 hour interval 4, 5, 6, 4.