European Journal of Clinical Pharmacology

, Volume 62, Issue 9, pp 749–756

Detection of potential drug interactions – a model for a national pharmacy register

  • Bengt Åstrand
  • Emelie Åstrand
  • Karolina Antonov
  • Göran Petersson
Pharmacoepidemiology and Prescription

DOI: 10.1007/s00228-006-0143-x

Cite this article as:
Åstrand, B., Åstrand, E., Antonov, K. et al. Eur J Clin Pharmacol (2006) 62: 749. doi:10.1007/s00228-006-0143-x



The widespread use of pharmaceuticals prescribed by different physicians has caused the Swedish government to propose a new legislation with registration of all prescriptions dispensed at the Swedish pharmacies. In the present study, we wanted to examine the frequency, distribution and determinants of potential drug interactions.


The prescriptions from all individuals (n=8,214) with two or more prescriptions during October 2003 to December 2004 were collected from the ongoing Jämtland cohort study of a total of about 11,000 individuals. Potential drug–drug interactions were detected with a computerized interaction detection system and classified according to clinical relevance (types A–D).


On average each individual filled 14.6 (men 14.3, women 14.8) prescriptions during the study period. 3.6% of the individuals used more than 15 different drugs. The number of detected potential drug interactions type A–D was 4,941 (men 1,949, women 2,992). The risk of receiving a potential interaction type A–D was estimated as the cumulative incidence 0.26 (2,116/8,214) overall, 0.22 (748/3,467) for men and 0.29 (1,368/4,747) for women during the 15-month study period. The age adjusted risk, RRadj, for women was estimated as 1.30. Excluding sex hormones and modulators of the genital system, the RRadj was 0.96, with no elevated risk for women. For potential interactions type D, that might have serious clinical consequences, 167 (cumulative incidence 0.0203) individuals (72 men, cumulative incidence 0.0208, 95 women cumulative incidence 0.0200) were detected. The risk of receiving a combination of potentially interacting drugs was positively correlated to age and polypharmacy. The cumulative incidence for elderly was estimated as 0.36 (65–84 years) and 0.39 (85 years and above). The relative risk for individuals with 15 drugs or more was estimated as 3.67 (95% CI 3.46–3.90).


In a general population there were relatively few severe potential drug interactions. The new Swedish national pharmacy register will provide health care professionals with a powerful tool to systematically review all prescriptions. An alert system should focus on the more potential drug interactions, type C–D, with close monitoring of elderly and patients with polypharmacy.


Community pharmacy services Decision making, computer-assisted Drug interactions Drug/statistics and numerical data Drug therapy/adverse effects Drug utilization Humans Polypharmacy Prescriptions Sweden/epidemiology 

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Bengt Åstrand
    • 1
    • 5
  • Emelie Åstrand
    • 2
  • Karolina Antonov
    • 3
  • Göran Petersson
    • 4
  1. 1.Apoteket ABE-Health ServicesKalmarSweden
  2. 2.Faculty of PharmacyUppsala UniversityUppsalaSweden
  3. 3.Apoteket ABStatisticsStockholmSweden
  4. 4.Department of Health and Behavioural SciencesE-Health Institute, University of KalmarKalmarSweden
  5. 5.Apoteket ABKalmarSweden