Computerization of the Dutch Community Pharmacy System

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Chapter: Pharmacovigilance: Other Databases in Europe for the Analytic Evaluation of Drug Effects

Computerization of outpatient pharmacy records in the Netherlands is almost universal and so is (because of the patient’s habit to frequent only one pharmacy) the compilation of longitudinal prescription drug histories.


Computerization of outpatient pharmacy records in the Netherlands is almost universal and so is (because of the patient’s habit to frequent only one pharmacy) the compilation of longitudinal prescription drug histories. Although computerization has started for administrative (reimbursement) purposes, medi-cation surveillance and computerized stock holding and ordering have become important incentives for optimal registration of drug dispensing. Computer-ized medication surveillance tracks change in dosages of chronic medications, correct dosing (especially for elderly and children), contra-indications (deducted from previously prescribed medications) and interac-tions between concomitant medications. In case of ‘abnormal’ situations, a signal will be generated that needs to be verified by the pharmacist (Herings, 1993; Leufkens and Urquhart, 2005).

All information stored in pharmacy computers, independent of the employed software or hardware, is primarily based on the information written on a prescription order by a GP, dentist or specialist. The information that should be stated on this order is legally regulated and has to comprise the prescribed product, the date of prescription, name and resi-dence of prescriber, a patient identifier (name) and the daily dose regimen. For reimbursement purposes, the amount dispensed is also available on each prescription (Herings, 1993).

The longitudinal data collection in pharmacies, the completeness of data and the fact that all prescription drugs are recorded (independent of reimbursement) make these data a useful source for pharmacoepi-demiological research. They have served for national cohort tracking in case of drug alerts after which outcome data may be either linked or collected by ad hoc methods (Visser et al., 1996). The PHARMO database is based on pharmacy data and is unique in the Netherlands for its record linkage with national hospitalization registries and recently in subsets also with inpatient pharmacy data, laboratory, cancer and pathology registries (


The PHARMO record linkage system was devel-oped in the early 1990s by Herings and Stricker. It now includes the drug-dispensing records from community pharmacies and hospital discharge records of about 2 million community-dwelling inhabi-tants of 30 medium-sized cities in the Netherlands ( Until 2006, patients in the Nether-lands did not have a unique identifier. Therefore, the underlying source population is not exactly known, but it has been estimated by using information for each city from the Bureau of Statistics (CBS). Patients that are registered within the pharmacy files are regarded as non-residents and eliminated from the patient regis-ters if they did not have recorded a family practitioner residential in one of the cities. Patients are assumed to be present in the source population between the first and last encounter in the pharmacy. For all resi-dents, the drug-dispensing histories are linked on a yearly basis to the national hospital discharge records of the same patient, using a probabilistic algorithm, based on characteristics such as date of birth, gender and a code for the GP since no unique patient iden-tifier was present until 2006. Validation of the initial database in 1993 (nine cities) showed that these registries are linked with a sensitivity and specificity exceeding 95%, which is comparable with record linkage systems based on unique personal identifiers (Herings, 1993).

The computerized drug-dispensing histories con-tain outpatient prescription data concerning the dispensed drug, type of prescriber, dispensing date, dispensed amount, prescribed dose regimens and the legend duration (prescription length). The hospi-tal records include detailed information concerning the primary and secondary diagnoses, procedures and dates of hospital admission and discharge. All diagnoses are coded according to the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM). Recently, PHARMO RLS has been linked to national pathology data and a regional cancer registry. For subsets of the database linkage with in-hospital drug use and outpatient labo-ratory data as well as primary care data are also avail-able. Five years ago, the PHARMO record linkage system has been transferred from the Department of Pharmacoepidemiology and Therapeutics at Utrecht University to the PHARMO research institute.

The database has been used by the Department of Pharmacoepidemiology at Utrecht University and the PHARMO Institute for studies on drug utiliza-tion, persistence with treatment, economic impact and adverse drug reactions. For a complete updated list of publications that were based on PHARMO RLS data, the website can be inspected (

The impact of recent policy changes on the Dutch health care structure and quality of data in claims databases is unclear. The Dutch health care system is moving ahead in the direction of more market forces, freedom of choice by patients and more emphasis on cost containment and efficiency (Leufkens and Urquhart, 2005). The recording of diagnoses in the national registry of discharge diagnosis will change because of the introduction of a Diagnosis-Related Group (DRG) system, but the strong actuarial basis of the GP will continue. A national electronic patient record should exist by 2007 with the use of a unique national patient identifier. This identifier might facil-itate record linkage, but its introduction will rein-force privacy legislations that may actually negatively impact on the possibility to conduct record linkage studies.

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