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.1medication 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 . 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 can not 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 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 studies811 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 . 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 . 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 . 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 . 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 . 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 . 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 . from march 2007 to april 2007 , 734 unit dose medication cassettes were filled by pharmacy 
         technicians 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 . 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 . 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 . 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 be 
         interpreted with some caution . 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 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 studies2325 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 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 , 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 . 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 
         1year 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 . 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 . 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 .
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 : 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 . 
 results : 
 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 . 
 conclusions : 
 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 .