Table 10.1. Studies evaluating the impact of unit-dose dispensing on medication errors*

StudyStudy Design, Outcomes** Results: Error Rates (95% CI)
Hynniman, 1970 23 Cross-sectional comparison between study hospital and non-randomly selected "comparison" hospitals (Level 3)
Errors of commission and omission (Level 2) among doses ordered
Unit-dose system: 3.5% (3.1-4.0%)
Conventional distribution systems at 4 hospitals:
8.3% (7.1-9.7%)
9.9% (8.0-12.2%)
11.4% (9.9-13.2%)
20.6% (18.4-22.9%)
Means, 1975 13 Simborg, 1975 14 *** Cross-sectional comparison of 2 wards within a single hospital over a 60-day period (Level 3)
Errors of commission (Level 2) among doses administered during randomly chosen observation periods
Unit-dose ward: 1.6% (1.0-2.5%)
Multi-dose ward: 7.4% (6.1-8.9%)§
Schnell, 1976 24 Prospective before-after study (Level 2) at four Canadian hospitals
Errors observed during medication preparation and administration (Level 2)
Before vs. after implementation of unit-dose system: 37.2 vs. 38.5%;
42.9 vs. 23.3%;
20.1% vs. 7.8%;
38.5% vs. 23.1%¶
Dean, 1995 22 Cross-sectional comparison (Level 3) of US and UK hospitals with different pharmacy distribution systems
Errors observed during medication administration (Level 2)
84 errors among 2756 observations in UK hospital using traditional ward stock system: 3.0% (2.4-3.7%)
63 errors among 919 observations in US hospital using unit-doses and automated dispensing: 6.9% (5.2-8.5%)
Absolute difference: 3.9% (2.1-5.7%)
Taxis, 1998 25 Cross-sectional comparison (Level 3) of 2 hospitals in Germany and one hospital in the UK
Errors observed during medication administration
UK hospital using traditional ward stock system: 8.0% (6.2-9.8%)
German hospital using traditional ward stock system: 5.1% (4.4-5.8)
German hospital using unit-dose system: 2.4% (2.0-2.8%)
Omission was the most common type of error

* CI indicates confidence interval.

** Errors of commission include administration of wrong dose or wrong or unordered drug, whereas errors of omission include missed doses for inclusion in a patient's unit-dose drawer or a dose not administered.

*** As outlined in the text, the similarities in study setting, time, design and results suggest that these 2 references contain data from the same study; information from these references was therefore combined and treated as a single study.

§ The 95% CIs shown in the table were calculated using the reported data: 20 errors in 1234 observed doses on the unit-dose ward vs. 105 errors in 1428 observed doses on the multidose ward.

¶ When wrong time errors were omitted, the above results changed so that the change to a unit-dose was associated with a significant increase in errors at the first hospital, a non-significant decrease in errors at the second hospital, and significant decreases in errors at the other two hospitals.

From: 10, Unit-Dose Drug Distribution Systems

Cover of Making Health Care Safer
Making Health Care Safer: A Critical Analysis of Patient Safety Practices.
Evidence Reports/Technology Assessments, No. 43.
Shojania KG, Duncan BW, McDonald KM, et al., editors.

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