JRSM > Volume 97, Number 8 > Pp. 380-383

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Doctors' confusion over ratios and percentages in drug solutions: the case for standard labelling

Daniel Wren Wheeler MRCP FRCA  ¹ Dionysios Dennis Remoundos MB BChir  ² Kim David Whittlestone BVetMed  ³ Michael Ian Palmer PhD FRCA  ⁴ Sarah Jane Wheeler MA MRCP  ¹ Timothy Richard Ringrose MRCP  ⁵   David Krishna Menon PhD FRCA  ¹

¹ University Department of Anaesthesia, University of Cambridge
² Department of Medicine, Norfolk and Norwich University Hospital, Norwich
³ Clinical and Biomedical Computing Unit, University of Cambridge
⁴ Department of Anaesthetics, West Suffolk Hospital, Bury St Edmunds
⁵ doctors.net.uk, Abingdon, Oxfordshire, UK

Correspondence to: Dr D W Wheeler, Clinical Lecturer in Anaesthesia, University Department of Anaesthesia, Box 93, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, UK E-mail: dww21{at}cam.ac.uk

The different ways of expressing concentrations of drugs in solution, as ratios or percentages or mass per unit volume, are a potential cause of confusion that may contribute to dose errors. To assess doctors' understanding of what they signify, all active subscribers to doctors.net.uk, an online community exclusively for UK doctors, were invited to complete a brief web-based multiple-choice questionnaire that explored their familiarity with solutions of adrenaline (expressed as a ratio), lidocaine (expressed as a percentage) and atropine (expressed in mg per mL), and their ability to calculate the correct volume to administer in clinical scenarios relevant to all specialties.

2974 (24.6%) replied. The mean score achieved was 4.80 out of 6 (SD 1.38). Only 85.2% and 65.8% correctly identified the mass of drug in the adrenaline and lidocaine solutions, respectively, whilst 93.1% identified the correct concentration of atropine. More would have administered the correct volume of adrenaline and lidocaine in clinical scenarios (89.4% and 81.0%, respectively) but only 65.5% identified the correct volume of atropine.

The labelling of drug solutions as ratios or percentages is antiquated and confusing. Labelling should be standardized to mass per unit volume.

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