Can medical students calculate drug doses?

  • CS Harries


Objectives: A doctor’s ability to calculate drug doses is a skill that is generally assumed. We assessed medical students’ performance when given four types of dosing calculations typical of those required in an emergency setting.
Design: Longitudinal study. Setting and subjects: Students were assessed at the beginning of the third year, and repeatedly during the third and fourth year while receiving training in dosage calculations. Competence was defined as correctly answering all four categories of calculation at any one time, i.e. a score of 100%. Failure to respond correctly to the individual questions was also analysed because an incorrect calculation could be equated with a “patient” receiving a wrong dose.
Outcome measures: Outcome measures were the percentage of students achieving competence and the proportion of times students showed competence relative to their total number of opportunities. A further outcome was the percentage of calculations incorrect i.e. potential “patients” harmed. Results: Of the 364 students, 23% were competent at the beginning, while 66% achieved competence at least once by the end of the study. Students were competent 31% of the time and calculated the wrong dose for 34% of “patients”. Eightytwo students were competent at baseline, 157 became competent and 125 never achieved competence. They calculated the wrong dose for 9%, 31% and 51% of “patients” respectively. Although race and home language were predictors of performance at baseline, both associations had been lost by the time competence was achieved. All students experienced the most difficulty with calculations when the drug concentration was expressed either as a ratio or a percentage.
Conclusion: Our findings support calls for the standardised labelling of drugs in solution and for dosage calculation training in the medical curriculum.

Keywords: drug dosage calculations, clinical competence, medication errors

South Afr J Anaesth Analg 2013;19(5):248-251

Author Biography

CS Harries
Division of Pharmacology, Discipline of Pharmaceutical Sciences College of Health Sciences, University of KwaZulu-Natal

Journal Identifiers

eISSN: 2220-1173
print ISSN: 2220-1181