From prescriptions to drug use periods - things to notice.
BACKGROUND
Electronic prescription registers provide a vast data source for pharmacoepidemiological research. Prescriptions as such are not suitable for all research purposes; e.g., studying concurrent use of different drugs or adverse drug events during current use. For those purposes, data on dispensed prescriptions needs to be transformed to periods of drug use.


METHODS
We used 3,828,292 dispensed prescriptions claimed between 1 January 2002 and 31 December 2009 for 28,093 persons with Alzheimer's disease. Examples of drug use histories are presented to discuss different aspects that should be noticed when using register-based data consisting of drug purchases.


RESULTS
There is no simple method for correctly transforming dispensed prescriptions to periods of drug use that is usable for all drugs and drug users. Fixed assumptions of daily dose (in defined daily doses, tablets or other units) and fixed time windows should be used with caution and adjusted for different drug use patterns.


CONCLUSIONS
We recommend that when transforming prescription drug purchases to drug use periods personal dose, purchasing pattern and other behavioral differences between patients should be taken into account.
Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. antti.tanskanen@ki.se.
Antti
A
Tanskanen
Heidi
H
Taipale
Marjaana
M
Koponen
Anna-Maija
AM
Tolppanen
Sirpa
S
Hartikainen
Riitta
R
Ahonen
Jari
J
Tiihonen
D000544:Alzheimer Disease / Q000188:drug therapy; D015283:Citalopram / Q000627:therapeutic use; D004232:Diuretics / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004348:Drug Labeling; D011307:Drug Prescriptions; D006801:Humans; D019808:Losartan / Q000627:therapeutic use; D008790:Metoprolol / Q000627:therapeutic use; D004364:Pharmaceutical Preparations; D013607:Tablets; D013693:Temazepam / Q000627:therapeutic use; D013997:Time Factors
D004232:Diuretics; D004364:Pharmaceutical Preparations; D013607:Tablets; D015283:Citalopram; D013693:Temazepam; D008790:Metoprolol; D019808:Losartan