PEBC MCQ Prescription Review & Dispensing question: year old after hip surgery reads Morphine

PEBC MCQPrescription Review & Dispensing

A prescription for a 70 year old after hip surgery reads 'Morphine 5.0 mg po q4h prn pain'. Which ISMP Canada concern applies to how the dose is written?

a. Doses must always be written in words
b. 'po' should never be used for oral drugs
c. The trailing zero could be misread as 50 mg
d. 'prn' is not allowed on narcotic prescriptions

Show the answer and explanation

Answer: c. The trailing zero could be misread as 50 mg

ISMP Canada's 'Do Not Use' list includes trailing zeros (5.0 mg) because the decimal point can be missed, turning 5 mg into 50 mg, a tenfold overdose; the dose should be written as 5 mg. Leading zeros are required for doses below 1 (0.5 mg). 'po' and 'prn' are common accepted abbreviations, although written-out directions are good practice. Source: ISMP Canada, Do Not Use: dangerous abbreviations, symbols and dose designations (updated 2023); Accreditation Canada ROP on abbreviations (2024).

Common mistake

Not recognising trailing zeros as an error-prone expression.

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Original practice material written to the public PEBC blueprint; not a past or real exam question. Not affiliated with or endorsed by The Pharmacy Examining Board of Canada (PEBC). Educational practice material for exam preparation only. Not medical advice and not a substitute for current product monographs, clinical guidelines or professional judgement. Questions have not yet been reviewed by a licensed pharmacist.