In Estonia, warfarin is widely prescribed by general practitioners to prevent and treat thromboembolic diseases. To date, there has been no systematic analysis of the potential risk of warfarin interactions with other drugs in the outpatient population.ObjectiveThe aim of the study was to analyze the incidence of potential interactions in prescription schemes in Estonia in a cohort of outpatients receiving warfarin treatment.MethodsThe retrospective study population included 203,646 outpatients aged 50 years or older of whom 7,175 received warfarin therapy. Patients who had used at least one prescription drug for a minimum period of 7 days concomitantly with warfarin were analyzed. Potential drug interactions were analyzed using Epocrates online, Stockley's Drug Interactions and domestic drug interaction databases. ResultsThe average number of drugs used concomitantly with warfarin was 4.8 (SD=1.9) (males: 4.7 SD=2.0, females: 4.9 SD=2.0). No potential interactions in treatment regimens were found in 38% of patients, one potential interaction was observed in 29% and two or more potential interactions were observed in 33% of patients. The mean number of all potential interactions was 1.2 per patient and about the same in men and women. Potential interactions were associated with the number of drugs. Warfarin-related interactions were detected in 57% of patients, and the number of interactions related to warfarin per patient varied from 1 to 5. Most frequent were use of warfarin with NSAIDs (14%), followed by simvastatin (9%) and amiodarone (7%). ConclusionsThis study shows that 57% of outpatients in Estonia receiving warfarin have drugs potentially interacting with warfarin in their treatment schemes. Most interactions (14%) with warfarin are associated with the prescription of NSAIDs.

In Estonia, HMG-CoA reductase inhibitors are widely used to modify lipid levels but there are no current data on additional medicines prescribed alongside the statins. The aim of this study was to identify the frequency of potential clinically relevant interactions at a national level among an outpatient population treated with statins between January and June 2008, based on the prescription database of the Estonian Health Insurance Fund. This retrospective prevalence study included 203,646 outpatients aged 50 years or older, of whom 29,367 received statin therapy. The study analysed individuals who had used at least one prescription medicine for a minimum of 7 days concomitantly with statins. Potential drug interactions were analysed using Epocrates online, Stockley’s Drug Interactions, and the drug interaction database developed in Estonia. Statins metabolised by the CYP3A4 isoenzyme were prescribed to 64% of all statin users. Medicines known to have potentially clinically significant interactions with statins were prescribed to 4.6% of patients.The drugs prescribed concomitantly most often with simvastatin were warfarin (5.7%) and amiodarone (3.9%), whereas digoxin (1.2%) and ethinylestradiol (2%) were prescribed with atorvastatin.Potential interactions were not detected in the treatment regimens of rosuvastatin, pravastatin, and fluvastatin users.

During the last decades, the share of population using prescription (Rx) medicines has considerably increased. With the wider introduction of self-medication and the use of over-the-counter (OTC) medicines, there is a real threat for drug-drug interactions between Rx and OTC medicines neither identified nor overseen by healthcare specialists.The objectives of this survey were to ascertain how often, and for what conditions OTC and Rx medicines are used simultaneously, and to discuss possible health hazards connected with the concomitant use of these medicines.This survey was designed as a descriptive, cross-sectional questionnaire-based interview which was conducted amongst pharmacy customers and patients in urban and rural areas of Estonia in between 2010–2012.In total, 712 respondents participated in the survey. Of those, 50.4% reported concomitant use of Rx and OTC medicines during the survey. The simultaneous use of Rx and OTC medicines increased with age and the number of chronic diseases (both p < 0.001). Of chronic patients, 37.1% used Rx and OTC medicines on a daily basis over a four-week period before the survey, and considering reported chronic diseases and the most widespread OTC medicines, they could encounter drug-drug interactions between Rx medicines (e.g. antihypertensives, anti-inflammatory medicines) and OTC medicines (e.g. paracetamol, NSAID-s, herbal medicines and adsorbents).The present survey revealed frequent concomitant use of Rx and OTC medicines. Especially vulnerable are chronic and elderly patients. In the future, both patients and healthcare specialists should pay more attention to possible drug-drug interactions of Rx and OTC medicines.

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