WHO defined daily doses versus hospital-adjusted defined daily doses: Impact on results of antibiotic use surveillance

Abstract

Objectives: To investigate effects on surveillance results of hospital antibiotic use when WHO defined daily doses (WHO DDDs) are adjusted to doses recommended for hospitalized patients [hospital-adjusted defined daily doses (haDDDs)]. Methods: Datafor antibiotic use in 2006-11 for all 22 Norwegian Health Enterpriseswere analysed with bothWHO DDDs and haDDDs as numerators. The haDDDswere determined fromrecommendations given in regional and national guidelines on antibiotic use in hospitals. The twoways of calculating the amount of antibiotic use were compared, with either the number of bed days (BDs) or the number of discharges as the denominator. The drug utilization 90% methodology was applied for ranking the use of the various antibiotics. Results: DDD adjustments altered the figures for total antibiotic use from 67.1 WHO DDDs/100 BDs to 49.3 haDDDs/100 BDs (226.4%). The most marked difference was found for penicillins: 31.1 WHO DDDs/100 BDs versus 13.4 haDDDs/100 BDs (256.8%). The corresponding figures for broad-spectrum antibiotics were 17.3 and 15.5 (210.4%), respectively; for these antibiotics, the conversion changes varied significantly between institutions, from 216.7% to 23.3%. Ranking antibiotic use based on haDDDs resulted in higher positions for metronidazole, cefuroxime, cefotaxime and cefalotin/cefalexin compared with the WHO DDD-based ranking, where the penicillins dominated. Conclusions: The low-set WHO DDDs for penicillins caused skewed surveillance results that concealed the real magnitude of broad-spectrumantibiotic use and distorted interhospital comparisons. For surveillance of antibiotic use in hospitals, WHO DDDs should be supplemented with haDDDs. © The Author 2013. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.