Dextromethorphan-Guaifenesin Syrup Dispensing Calculation for 7 Days
Dispense 210 mL of Dextromethorphan-Guaifenesin 5-50 mg/5mL syrup for a 7-day supply when dosed at 5 mL every 4 hours as needed.
Calculation Methodology
The dosing regimen specifies 5 mL every 4 hours as needed, which translates to a maximum of 6 doses per 24-hour period (24 hours ÷ 4 hours = 6 doses). For practical dispensing purposes when medication is prescribed "as needed," the standard approach is to calculate based on maximum potential usage to ensure adequate supply.
Daily Maximum Calculation
- Doses per day: 6 doses (every 4 hours around the clock)
- Volume per dose: 5 mL
- Daily maximum volume: 6 doses × 5 mL = 30 mL per day
Seven-Day Supply Calculation
- Total volume needed: 30 mL/day × 7 days = 210 mL
Clinical Context and Safety Considerations
The maximum recommended daily dose of dextromethorphan is 120 mg for adults, which at this concentration (5 mg/5mL) equals 120 mL of syrup daily. 1, 2 The prescribed regimen of 5 mL every 4 hours (maximum 30 mL daily = 30 mg dextromethorphan) falls well within safe dosing parameters.
Important Dispensing Notes
- This formulation contains both dextromethorphan (antitussive) and guaifenesin (expectorant) in a 5-50 mg/5mL concentration 3, 4
- The "as needed" designation means patients may use less than the calculated maximum, but dispensing should account for full potential usage
- Standard pharmacy practice for "as needed" medications typically dispenses based on maximum frequency to prevent early refill requests and ensure therapeutic availability
Abuse Potential Awareness
While this specific dose is therapeutic, pharmacists should be aware that dextromethorphan has abuse potential, particularly among adolescents who may consume megadoses (5-10 times the recommended dose) for dissociative effects. 1 However, the prescribed regimen of 5 mL every 4 hours represents appropriate therapeutic use for cough suppression.
Final Answer: Dispense 210 mL