PEBC MCQ Pharmaceutical Calculations question: mg/kg/day orally divided twice daily

PEBC MCQPharmaceutical Calculations

A prescription for KT, a 4 year old weighing 18 kg, reads: amoxicillin 90 mg/kg/day orally divided twice daily. The pharmacy stocks amoxicillin suspension 250 mg/5 mL. What volume should be given for each dose?

a. 8.1 mL
b. 10.1 mL
c. 10.8 mL
d. 16.2 mL

Show the answer and explanation

Answer: d. 16.2 mL

Daily dose = 90 mg/kg/day x 18 kg = 1,620 mg/day; divided twice daily = 810 mg per dose. At 250 mg/5 mL (50 mg/mL), 810 mg / 50 mg/mL = 16.2 mL per dose. Dividing the daily dose three times a day gives 10.8 mL, 8.1 mL halves the dose twice, and 10.1 mL assumes a 400 mg/5 mL product that is not what is stocked. Source: Health Canada Drug Product Database, amoxicillin oral suspension 250 mg/5 mL product monograph (checked 2026); Canadian Paediatric Society, Management of acute otitis media in children six months of age and older (Paediatr Child Health 2016, reaffirmed 2024), high-dose amoxicillin 75-90 mg/kg/day divided twice daily.

Common mistake

Forgetting to divide the total daily dose by the number of doses.

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