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

  • Pharmacoepidemiology and Prescription
  • Published:
European Journal of Clinical Pharmacology Aims and scope Submit manuscript

Abstract

Objective

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.

Methods

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).

Results

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).

Conclusion

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.

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Acknowledgements

We are indebted to Sten-Erik Öhlund for developing the interaction detection software, to Mats Nordlöf for construction of Figs. 1 and 2 and to Apoteket AB for providing the crude data from the Jämtland study. The study was supported financially by Apoteket AB, including support to the E-Health Institute.

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Authors and Affiliations

  1. Apoteket AB, E-Health Services, Kalmar, Sweden

    Bengt Åstrand

  2. Faculty of Pharmacy, Uppsala University, Uppsala, Sweden

    Emelie Åstrand

  3. Apoteket AB, Statistics, Stockholm, Sweden

    Karolina Antonov

  4. Department of Health and Behavioural Sciences, E-Health Institute, University of Kalmar, Kalmar, Sweden

    Göran Petersson

  5. Apoteket AB, 391 28, Box 873, Kalmar, Sweden

    Bengt Åstrand

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  1. Bengt Åstrand
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  2. Emelie Åstrand
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Correspondence to Bengt Åstrand.

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Åstrand, B., Åstrand, E., Antonov, K. et al. Detection of potential drug interactions – a model for a national pharmacy register. Eur J Clin Pharmacol 62, 749–756 (2006). https://doi.org/10.1007/s00228-006-0143-x

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