Adherenec and persistence with antihypertensive drugs

The aim of this thesis was to assess the prevalence and determinants of non-adherence and non-persistence with antihypertensive drugs and to provide suggestions for intervening to improve it among non-adherent patients with hypertension. This thesis is divided into three parts. The first part describes methodological issues with regard to the use of pharmacy records to detect several problems concerning adherence and persistence. If a prescription database lacking diagnoses is used to study antihypertensive drugs in relation to hypertension treatment, the results have to be interpreted with caution because of the potential misclassification that may occur. Subdividing the antihypertensive drug classes into subgroups decreases this misclassification. In literature, different methods of calculating persistence are used. The method used and the variation within a method influenced both persistence and the association between patient characteristics and persistence. The second part describes the prevalence of non-adherence and identification of potential targets for interventions in an observational setting. Uncontrolled blood pressure as well as patients' complaints about the prescribed medication may lead to modification of the initially prescribed antihypertensive drug regimen. Among patients who start using antihypertensive monotherapy, non-adherence is significantly associated with the occurrence of change in antihypertensive medication regimen. In addition, among patients who start antihypertensive monotherapy, non-adherence is often followed by discontinuation. Among a total of 2,325 patients who started using antihypertensive drugs in 1992, 39% used continuously during the 10 years of follow-up. About 22% temporarily discontinued and restarted treatment, whereas 39% of the patients discontinued permanently. Among a total of 35,714 patients who started using antihypertensive treatment during the period January 1st 1999 to June 30th 2004, 18,357 (51.4%) patients discontinued treatment. Of these patients, 19.3% restarted treatment within one year and 60.7% restarted within six years. In an international comparison, the proportion of patients with at least 180 days without medication was 23.3% in Pennsylvania, 23.4% in British Columbia and 24.0% in The Netherlands after one year. After six years, this percentage increased to 41.1, 36.3 and 38.2, respectively. This suggests that the problem of non-persistence transcends international boundaries, health system characteristics and prescription drug coverage policies. Adherence or persistence to treatment should be considered in the choice for a specific treatment. Two Mutiple Criteria Decision Making-models, Simple Additive weighting and Technique for Order Preference by Similarity to an Ideal Solution were evaluated for objectifying this consideration among internists, cardiologists, pharmacists and general practitioners. Among all professionals, according to both SAW and TOPSIS, ACE-inhibitors were ranked the first-line antihypertensive drug class. The last part concerns intervening in patients using chronic treatment, with special emphasis being placed on antihypertensives. From a review of pharmacist-led interventions to increase adherence to treatment, it was impossible to identify an overall successful adherence-improving strategy. The Medication Event Monitoring System as an intervention by community pharmacists among non-adherent patients with hypertension was associated with a non-significantly lower systolic and diastolic blood pressure after 3 months. Generic substitution of antihypertensive drugs in daily practice does not lead to lower adherence, or to more non-persistence and cardiovascular disease related hospitalizations