SUMMARYThe 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.

Doctors and medical students are more likely to make errors in drug dose calculations when the strengths of drug solutions are expressed as ratios or percentages. We have already described how a doctor's specialty influences their drug dose calculation skills, having surveyed almost 3000 doctors in an online survey. Better teaching of drug administration skills or reinforcement of existing skills would appear to be needed. We sought to identify doctors that might benefit particularly from such teaching by other means than specialty alone, by subjecting existing data to further analysis. Almost 3000 doctors subscribing to a UK-based internet content provider had participated in an online questionnaire concerning drug-dose calculation. Each doctor's score in the multiple choice questionnaire was cross referenced with demographic data obtained from the hosts of the original survey whilst maintaining anonymity. Newly and recently qualified doctors, and doctors working in the community, struggled most with the calculations (p < 0.0001). There were also highly significant differences in the performances of doctors from different medical schools (p < 0.0001). As a new training programme for junior doctors is being introduced in the UK; we recommend that drug administration skills are given a prominent place in the curriculum, and again call for the standardisation of ampoule labelling to mass concentration.

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.