Frequency, types, and potential clinical significance of medication-dispensing errors.

Abstract

Many dispensing errors occur in the hospital, and these can endanger patients. The purpose of this study was to assess the rate of dispensing errors by a unit dose drug dispensing system, to categorize the most frequent types of errors, and to evaluate their potential clinical significance.
A prospective study using a direct observation method to detect medication-dispensing errors was used. From March 2007 to April 2007, 'errors detected by pharmacists' and 'errors detected by nurses' were recorded under six categories: unauthorized drug, incorrect form of drug, improper dose, omission, incorrect time, and deteriorated drug errors. The potential clinical significance of the 'errors detected by nurses' was evaluated.
Among the 734 filled medication cassettes, 179 errors were detected corresponding to a total of 7249 correctly fulfilled and omitted unit doses. An overall error rate of 2.5% was found. Errors detected by pharmacists and nurses represented 155 (86.6%) and 24 (13.4%) of the 179 errors, respectively. The most frequent types of errors were improper dose (n = 57, 31.8%) and omission (n = 54, 30.2%). Nearly 45% of the 24 errors detected by nurses had the potential to cause a significant (n = 7, 29.2%) or serious (n = 4, 16.6%) adverse drug event.
Even if none of the errors reached the patients in this study, a 2.5% error rate indicates the need for improving the unit dose drug-dispensing system. Furthermore, it is almost certain that this study failed to detect some medication errors, further arguing for strategies to prevent their recurrence.

Full text

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CLINICS 2009;64(1):11-6
CLINICAL SCIENCE
Hôpital d’Instruction des Armées PERCY - Clamart Cedex, France.
Email: xavier.bohand@hotmail.fr
Tel.: 33 0 141 466 340
Received for publication on July 22, 2008
Accepted for publication on September 15, 2008
FrEquENCy, typES, ANd potENtIAL CLINICAL
SIgNIFICANCE oF mEdICAtIoN-dISpENSINg
ErrorS
Xavier Bohand, Laurent Simon, Eric Perrier, Hélène Mullot, Leslie Lefeuvre,
Christian Plotton

doi: 10.1590/S1807-59322009000100003
Bohand X, Simon L, Perrier E, Mullot H, Lefeuvre L, Plotton C. Frequency, types, and potential clinical significance of
medication-dispensing errors. Clinics. 2009;64(1):11-6.
INTRODUCTION AND OBJECTIVES: Many dispensing errors occur in the hospital, and these can endanger patients. The
purpose of this study was to assess the rate of dispensing errors by a unit dose drug dispensing system, to categorize the most
frequent types of errors, and to evaluate their potential clinical significance.
METHODS: A prospective study using a direct observation method to detect medication-dispensing errors was used. From March
2007 to April 2007, “errors detected by pharmacists” and “errors detected by nurses” were recorded under six categories: unau-
thorized drug, incorrect form of drug, improper dose, omission, incorrect time, and deteriorated drug errors. The potential clinical
significance of the “errors detected by nurses” was evaluated.
RESULTS: Among the 734 filled medication cassettes, 179 errors were detected corresponding to a total of 7249 correctly ful-
filled and omitted unit doses. An overall error rate of 2.5% was found. Errors detected by pharmacists and nurses represented 155
(86.6%) and 24 (13.4%) of the 179 errors, respectively. The most frequent types of errors were improper dose (n = 57, 31.8%) and
omission (n = 54, 30.2%). Nearly 45% of the 24 errors detected by nurses had the potential to cause a significant (n = 7, 29.2%)
or serious (n = 4, 16.6%) adverse drug event.
CONCLUSIONS: Even if none of the errors reached the patients in this study, a 2.5% error rate indicates the need for improv-
ing the unit dose drug-dispensing system. Furthermore, it is almost certain that this study failed to detect some medication errors,
further arguing for strategies to prevent their recurrence.
KEYWORDS: Adverse Event; Drug Error; Patient security; Risk Management; Unit Dose.
INTRODUCTION
Reducing the incidence of drug-related iatrogenic disease
is a public health concern in France and around the world.
Reports on the quality of care by the USA Institute of
Medicine, found that in the USA, over one million injuries and
at least 44 000 deaths occur annually as a result of medical
errors. Particularly in the USA medication errors cause over
7 000 deaths per year and result in adverse effects in 2% of
in-hospital patients.1 Medication errors are recognized as a
major cause of medical errors, which can harm patients and
induce adverse drug events (ADEs).2,3 Furthermore in the
USA medication errors compromise patient confidence in
the health care system and increase health care costs. Bates
et al. 4 estimated that 0.3 medication errors occur per patient
per day and approximately 1% of medication errors cause
an ADE. In an intensive care unit, also in the USA, Kopp et
al.5 identified one error for every five doses of medication
administered. Notably, the outcome or clinical significance
of many medication errors may be minimal, with few or no
consequences that adversely affect a patient. But, because
hospitalized patients are often critically ill, some medications
errors cannot be taken lightly. In a large study conducted in
11 medical and surgical units in two tertiary care hospitals
in the USA, Bates et al.6 found that 42% of serious and life-
threatening ADEs were preventable.
Medication errors are an important clinical problem that

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CLINICS 2009;64(1):11-6Medication dispensing errors
Bohand X et al.
can occur at every stage of the drug delivery process.7 Effective
systems for prescribing, dispensing, and administering
medications should be established with safeguards to prevent
errors. Dispensing errors are usually associated with poor
safety and inefficient dispensing systems. Despite various
methodologies, several previous studies8-11 have reported
rates of pharmacy-dispensing errors detected by pharmacists
ranging from 1.0% to 2.9%. In a 4-year study in the USA,
Roland12 reported 82 dispensing errors, two of which were
considered major errors and resulted from incorrect drug
selection. However, this study relied on self-reporting to detect
dispensing errors and probably underestimated the incidence
of these errors. Klein et al.13 compared error rates for a manual
dispensing system and an automated one and found error rates
of 0.84% and 0.65%, respectively. Thus, detecting dispensing
errors should be a component of the pharmacy’s routine
quality control. Even if the hospital pharmacy’s medication
dispensing process is recognized as a source of medication
errors and potential ADEs, the potential for patient harm
is rarely evaluated. For the sake of efficiency, pharmacy
technicians fill the medication cassettes of a unit dose drug-
dispensing system, and then pharmacists check their work. In
March 2007, in order to achieve the highest possible safety
level, the cardiovascular department of the Percy military
hospital established a unit dose drug-dispensing system
unusual for France. The purpose of the present study was to
assess the rate of dispensing errors in this central pharmacy
and in the cardiovascular department as a whole. The analysis
examined the most frequent types of errors and evaluated their
potential clinical significance.
MATERIALS AND METHODS
Setting
The study was conducted in the central pharmacy and
cardiovascular department (30 beds) of the 354-bed Percy
military hospital in Clamart (France) during the two-month
period of March and April, 2007. The study followed the
dispensing activities of the pharmacy between 8 a.m. and 6
p.m. from Monday to Friday. In the central pharmacy, drugs
were dispensed over the weekend, but not prescriptions were
accepted. Every day, the medical staff brought photocopies of
all written physicians’ prescriptions to the central pharmacy.
Handwritten prescriptions were clinically reviewed, modified
if necessary, and approved by a pharmacist. After pharmacist
approval, a pharmacy technician filled the medication cassette
using the original approved (or modified and approved)
prescription. Oral pharmaceutical forms were dispensed
in aliquots with enough tablets or capsules for one patient
for 24 hours, in a unit dose medication cassette made up of
4 compartments: morning, midday, evening and night. At
the end of the drug-filling process, pharmacists examined
medication cassettes. Dispensing errors defined as errors
detected by pharmacists (EDPs) were corrected before
delivery of the medication to the cardiovascular department.
In the cardiovascular department, nurses performed a second
check just before administering medications. Errors detected
by nurses (EDNs) were defined as technicians’ errors in filling
prescriptions that were missed by pharmacists but intercepted
and corrected by nurses. Pharmacy technicians, pharmacists,
and nurses were aware of the checks performed at the different
stages of the drug delivery process, but they were not informed
of the study and its purpose. During the study, the names of
the persons who committed the errors were not documented.
Moreover, during the study, pharmacists and nurses did not
share information about errors they had detected. All EDPs
and EDNs were recorded by an independent pharmacist
observer. In addition, both a physician of the cardiovascular
department and the pharmacist observer reviewed and
assessed the potential clinical significance of all EDNs. Each
reviewer determined whether the patient could have suffered
an injury if the dispensing error had not been intercepted by
nurses prior to administering the erroneous drug. A three-scale
classification system was used: no potential to cause an ADE,
potential to cause a significant ADE, or potential to cause a
serious ADE.
Definitions
For the purpose of this study, a dispensing error was
defined as any discrepancy between the interpretable written
prescription, including modifications made by a pharmacist
following contact with the physician or in accordance with
pharmacy policy, and the contents of the medication cassette.
The medication dispensing error rate was calculated by
dividing the total number of erroneous doses by the total
of filled and omitted doses. Errors were classified into six
categories according to type of error; the six error types were
taken from the American Society of Hospital Pharmacists:14
unauthorized drug error; incorrect dosage-form error;
improper dose error; omission error; incorrect time error;
deteriorated drug error. Doses were considered to have been
filled at the wrong time if they were dispensed in an incorrect
compartment of the medication cassette, e.g. if a dose was
mistakenly given in the morning compartment instead of the
evening compartment.
RESULTS
From March 2007 to April 2007, 734 unit dose
medication cassettes were filled by pharmacy technicians

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CLINICS 2009;64(1):11-6Medication dispensing errors
Bohand X et al.
and checked by both pharmacists and nurses. During the
study, 179 errors were detected, corresponding to a total of
7249 unit doses filled (n = 7195) and omitted (n = 54) in
medication cassettes. The overall dispensing error rate was
2.5%, corresponding to approximately 0.24 dispensing errors
detected per medication cassette. At the first step of the
error-checking process, pharmacists failed to detect 13.4% (n
= 24) of all technicians’ errors when filling prescriptions.
Table 1 indicates the types of dispensing errors detected
during the 2-month period. Improper dose errors and
omission errors occurred in 57 (31.8%) and 54 (30.2%) of
the 179 reported dispensing errors, respectively. Omission
errors (n = 51, 32.9%), improper dose errors (n = 44, 28.4%)
and incorrect time errors (n = 36, 23.2%) accounted for
84.5% of the 155 EDPs.
Among the 24 EDNs registered, the most common
error types were improper dose errors (n = 13, 54.2%)
and unauthorized drug errors (n = 5, 20.8%). Examples
of improper dose EDNs included prescriptions for
amlodipine filled at 10 mg instead of 5 mg, prescriptions
for acetylsalicylic acid filled at 500 mg instead of 1000
mg, and prescriptions for acenocoumarol filled at 1 mg
instead of 2 mg. Most of the unauthorized drug selections
detected by nurses involved drug names that sounded alike
or looked alike, or drugs with similar packaging, such as
confusion between CORVASAL 2 mg (molsidomine) and
COVERSYL 2 mg (perindopril). Incorrect dosage-form
errors (n = 2, 8.3%) included dispensing of a non-controlled-
release formulation of verapamil instead of a controlled-
release formulation.
Figure 1 indicates the potential clinical significance
of EDNs. Nearly 45% (n = 11) of the EDNs had the
potential to induce ADEs if they had not been intercepted;
16.6% (n = 4) could have caused serious ADE and 29.2%
(n = 7) could have led to a significant ADE. The most
common error types with a potential for serious ADEs were
unauthorized drug errors (n = 3). These three occurrences
involved the dispensing of 50 mg ketoprofene instead of
10 mg hydrocortisone to a 90-year-old man. The improper
dose error that could have led to a serious ADE involved
an 86-year-old woman’s prescription for verapamil 40 mg,
which was mistakenly filled at a dose of 240 mg.
DISCUSSION
An accurate dispensing system helps to prevent and
reduce medication errors by minimizing the opportunity
for dispensing errors in a pharmacy. In the 1960s, North
American hospital pharmacists developed the unit dose
system with the goal of reducing medication error rates
and drug costs and thus improving the quality of health
care.15 Indeed, the unit dose drug dispensing system
has a lower medication error rate than the ward stock
distribution system.16 We therefore sought to assess the
error rate of the unit dose system in our own hospital. Valid
meta-analyses regarding medication dispensing errors are
extremely difficult to perform because of differences in
clinical settings, factors measured, patient populations, and
drug dispensing methods. Although the direct observation
method utilized here is recognized as an efficient method
for detecting medication errors,17 our study results should
Table 1 - Types of medication-dispensing errors detected by pharmacists and nurses
Type of error
unauthorized
drug
incorrect
dosage-form
improper dose omission incorrect timedeteriorated
drug
Total
Errors detected by pharmacists (EDPs) 2204451 362155
Errors detected by nurses (EDNs)52 1331024
Total 2725754 372 179
% (of total errors) 15.1 1.1 31.8 30.220.71.1 100
Figure 1 - Potential clinical significance of medication dispensing errors
detected by nurses

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CLINICS 2009;64(1):11-6Medication dispensing errors
Bohand X et al.
be interpreted with some caution. First, our study was not
designed to completely account for all errors. Second, it
relied on human observers, who might have failed to detect
some dispensing errors. Consequently, the number of total
errors reported here likely underestimates the true overall
rate of dispensing errors.
Nevertheless, the results of our study show that a wide
range of errors occurred during the filling of medication
cassettes. Although similar studies differ from ours in some
of the methods and definitions, our results are comparable to
theirs. In their analysis of a unit dose drug-dispensing system
, Taylor et al.8 and Jornet-Montana et al.9 reported dispensing
error rates of 1.7% and 1.0%, respectively; however, they did
not evaluate dispensing errors missed by pharmacists. During a
2-week study of dispensing errors identified at the pharmacy’s
final check stage, Beso et al.10 found a 2.7% error rate. In a
study by Cina et al,11 5 075 pharmacy errors were made out of
a total of 140 755 doses filled by pharmacy technicians to an
overall pharmacy dispensing error rate of 3.6%. This overall
error rate could be broken down into 2.9% due to technicians’
errors when filling prescriptions, which were detected during
the pharmacist verification step; and 0.7% due to errors
intercepted after the pharmacist verification step.
The dispensing process therefore has inherent risks that
require improved procedures for detecting errors. Pharmacy
detection of dispensing errors may also provide ongoing
benefits by preventing potential ADEs in the medication
process. It is essential that the dispensing system involve
adequately trained and supervised health professionals,
adequate communication, and final checks performed
by separate individuals. Clearly, the check performed by
pharmacists remains necessary to reduce the occurrence
of all dispensing-related ADEs. Recognizing the incidence
and types of medication dispensing errors that occur in
a central pharmacy allows us to analyze their causes and
change the different stages of the process accordingly in
order to ensure maximal patient safety. In our study, the most
frequent error types were improper dose and omission errors.
These findings are consistent with previous studies that
indicate that improper dose and omission errors are among
the most frequent error types occurring at the dispensing
stage.8,18 One possible explanation is that technicians
perform an incomplete, incorrect, or rushed reading of
the prescription during the filling process. However,
most preventable injuries are not due to just one system
failure but result from breakdown at several points in the
dispensing system. Although causes were not systematically
recorded in this 2-month study, the multiplicity of factors
contributing to dispensing errors has been reported to include
communication failures, working environment, heavy
workload, distractions, failure to read the prescription, and
complex prescriptions involving several medical orders per
patient.19,20 Moreover, errors can arise because of similarities
in drug labeling and packaging, as well as similarities in
drug names; these similarities may explain unauthorized
drug errors, which pose a real threat to patient safety.
Because the clinical implications of medication
dispensing errors remain uncertain, preventive strategies to
reduce their occurrence should target all stages of the drug
delivery process. For example, the central pharmacy at Percy
hospital now implements some of the recommendations of
the National Coordinating Council for Medication Error
Reporting and Prevention21. For example, the noise level
was reduced, and the prescription check is performed in
a different area from the prescription filling. In order to
reduce unauthorized drug errors, incorrect dosage-form
errors and deteriorated drug errors, technicians are reminded
on a daily basis to perform an attentive reading of dosing
instructions. In addition, technicians and pharmacists share
information about the errors detected by technicians after
the filling process in order to prevent future errors. Finally,
to limit dispensing errors due to workload and distractions,
an additional pharmacy technician has been hired.
In our study, pharmacists failed to detect approximately
13% of medication selection errors made by technicians. A
similar result was found by Facchinetti et al.,22 who showed
that pharmacists were more accurate than nurses in checking
unit dose medication cassettes; nonetheless, pharmacists
failed to detect 100 of the 812 errors (12.3%) artificially
introduced into the unit dose distribution system. In the
study by Cina et al.,11 20.9% of all technician-filling errors
were overlooked by pharmacists during the verification
process. It is well known that a dispensing process relying
exclusively on repetitive human inspection is subject to
human fatigue; the pharmacists may find it difficult to
vigilantly check the medication cassettes. Adding a second
pharmacist verification step may therefore reduce the number
of dispensing errors overlooked by pharmacists. However,
an additional verification step may delay the delivery of
medication cassettes to the clinical unit. At Percy hospital,
the check is currently performed by pharmacists who spend
at least one hour per day on the verification process. Several
studies23-25 have shown that pharmacy technicians can check
medications in a unit dose distribution system without
compromising the accuracy. Thus, trained and certified
pharmacy technicians could safely and accurately check unit
dose medication cassettes filled by other technicians. The
results of our study and the major factors contributing to the
occurrence of dispensing errors have been explained to the
pharmacy technicians. In addition, Percy pharmacists have
developed a training program to teach technicians how to
reduce errors. Pharmacy technicians now perform the check

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Bohand X et al.
of unit dose medication cassettes under the supervision of
a pharmacist. While it seems evident that if pharmacists
miss errors, technicians will as well, but delegating this task
to technicians may probably increase their awareness of
dispensing errors. Moreover, this delegation should allow
pharmacists to spend additional time on clinical activities
and thereby contribute to pharmaceutical care.
One of the pharmacist’s missions is to ensure that patients
make the best use of medications. This is in accordance with
the Institute of Medicine’s recommendations 26, which seek to
improve the quality and safety of medication use. The report
lays out a blueprint for how pharmacists can become involved
in the medicine dispensing process in order to improve it. The
pharmacist should also lead collaborative, multidisciplinary
efforts to prevent, detect, and resolve medication errors and
drug-related problems and to educate patients about their
medication. Several studies27,28 have reported a decrease in
medication errors after implementing a program to improve
clinical pharmacy activity in medical care units.
In our study, poor handwriting may be considered
as a major source of error. Ambiguous, incomplete, or
confusing prescriptions may lead to poor understanding
of fundamental information necessary for correct drug
dispensing. Although introducing a computerized physician
order entry system can lead to its own types of errors,29
several studies have reported decreases in medication errors
with a computerized prescription system.30,31 A computerized
prescribing and dispensing system also provides other
advantages, since it can be integrated with a program that
will analyze the pharmacology of the prescriptions in
order to detect errors (e.g. dose errors, contraindications
because of other medicines being given to the same patient)
and inventory control software. At Percy hospital, the
planned implementation of a computerized prescription and
dispensing system is expected to decrease the incidence of
dispensing errors and increase the chances of intercepting
medications errors that do occur. Other new technologies,
such as bar-code medication systems32 and automated
medication-dispensing systems,13,33 have been shown to
reduce pharmacies’ dispensing error rates.
Undetected dispensing errors continue to be an important
concern. Even if none of the EDNs identified during our
study affected the patients’ health, 16.6% would have caused
serious ADEs. Some of these errors, especially unauthorized
drug errors, might have threatened patient health if they had
not been intercepted. Extrapolating our results to a 1–year
period indicates 140 EDNs, 24 of which could cause a
serious ADE. Similar to our study, the study of Cina et al.11
assessed the clinical significance of the errors undetected
by pharmacists. They found that 23.5% of these errors
would have caused ADEs, and 6.8% of these errors would
have caused serious or life-threatening ADEs. Although
differences in setting and methods make it challenging to
compare our study with that of Cina et al., both found the
most frequent errors with potential clinical significance
to be unauthorized drug errors and improper dose errors.
Furthermore, our study found that most errors with
significant or serious clinical severity concerned cardiology
medication and occurred primarily in elderly patients. These
results may reflect the fact that our study was carried out in
a cardiovascular department; the results may be different in
another clinical department.
Our study emphasized the need for nurses to intercept
dispensing errors. Because the check performed by nurses is
the last step before drug administration, it must be regarded
as a high-risk activity, especially since it has been shown
that nurses intercept only approximately 33% of serious
medication dispensing errors.34 Following the two-month
period of this study, the results were presented to the nursing
staff in order to enhance their awareness of dispensing errors,
of the potential clinical significance of such errors, and of the
usefulness of error reporting. Following the completion of
this study, every dispensing error detected and reported by
nurses is analyzed by several different specialists. Dispensing
errors reported by nurses must be seen by the pharmacy as
opportunities to identify areas for improvement. If changes
are made to the medication dispensing system, it is important
for the pharmacy staff to track the effects of those changes.
Lastly, reducing medication errors will require increased
emphasis on education about drug-related iatrogenic
disease.35 The teaching and training of health professionals
is recognized as an important tool to prevent mistakes and
increase patient safety.36 Since 2007, pharmacists at Percy
hospital have set up an educational program for nurses and
pharmacy technicians, which is part of the hospital’s general
policy of quality assurance and risk prevention.37 This one-
day educational program is conducted by a pharmacist.
Carried out using best practices and actual case studies,
the program aims to increase the awareness of nurses
and pharmacy technicians about preventing and detecting
medication dispensing errors.
CONCLUSIONS
This study increased the awareness of the pharmacy
and nursing staffs with regard to the reality and potential
severity of medication dispensing errors. Although none of
the errors registered during this study reached the patients,
the 2.5% error rate indicates a weakness in the unit dose
drug-dispensing system. Our hospital plans to improve the
dispensing system to reduce errors. Reducing dispensing
errors also depends on research into their causes.