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J Clin Pharm Ther. 2009 Aug;34(4):377-86. doi: 10.1111/j.1365-2710.2009.01021.x.

Potentially severe drug interactions in elderly outpatients: results of an observational study of an administrative prescription database.

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Laboratory of Quality Assessment of Geriatric Therapies and Services, and Drug Information Services for the Elderly, Istituto di Ricerche Farmacologiche Mario Negri, Milano, Italy.



To estimate the prevalence of potentially severe drug-drug interactions (DDIs) and their relationship with age, sex and number of prescribed drugs.


We analysed all prescriptions dispensed from 1 January 2003 to 31 December 2003 to individuals aged 65 or more registered under the Local Health Authority of Lecco, a northern Italian province with a population of almost 330 000 persons. Elderly who received at least two co-administered prescriptions were selected to assess the presence of DDIs.


The prevalence of potentially severe DDIs was 16%, and rose with increasing patient's age and number of drugs prescribed. At multivariate analysis, the adjusted odds ratios rose from 1.07 (95% CI 1.03-1.11) in patients aged 70-74 to 1.52 (95% CI 1.46-1.60) in those aged 85 or older. Elderly taking more than five drugs on a chronic basis had a statistically significant higher risk of sever DDIs than those receiving less than 3 or 3-5 such drugs.


The elderly constitutes a population at high risk of DDIs. As physicians still have some difficulty in managing this problem, it is essential to highlight for them, which factors raise the risk of DDIs.

[Indexed for MEDLINE]

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