Aim: To evaluate the effect of a letter intervention that was send to both the participants of a population screening and their general practitioners. We also tested what predicting variables influenced the GP to actually prescribe blood pressure lowering drugs (BPLD) or lipid lowering drugs (LLD).
Method: The study design was cross sectional, in the PREVEND outpatient clinic in Groningen University Hospital, the Netherlands. We used the clinical data of the 8592 subjects that participated in the first screening of the PREVEND study. Data on drug use was collected from community pharmacies. Drug use was measured the year before and after the screening with the subsequent intervention letter. As control population without intervention, we used the data from the InterAction DataBase (IADB) standardized for the population characteristics of the intervention group. The letter intervention was sent to participants who had shown after screening to have either an elevated blood pressure or plasma cholesterol, and the letter contained the advice to use a BPLD or LLD. Main outcome measures were proportion of patients prescribed BPLD and/or LLD in the year before and after the intervention, and variables that influence the GP to prescribe BPLD and LLD.
Results: Data from the community pharmacy were available from 7567 (88%) subjects. 397 participants (5.2%) received a letter with advice to start a BPLD, and 326 participants (4.3%) received a letter with advice to start a LLD. The prevalence of patients who were using BPLD and LLD before the intervention was not significantly different between the intervention and control group, 16.6 (CI 95% 15.8 -17.5) vs 16.0 and 4.8 (4.4-5.3) vs 4.6, respectively. After the letter intervention, the prevalence of BPLD use was higher in the intervention group compared with the control group (19.4 [18, 5-20, 3]vs 17.0%), as was the prevalence of LLD use (7.1[6.5-7.7) vs 5.4%). The same held true for the incidence of BPLD (3.4[3.0-3.8]vs 2.5%) and LLD use (2.1 [1, 6-2, 4]vs 1.0%), respectively, in the year after the intervention. Univariate and multivariate analysis showed that a higher blood pressure and cholesterol level, but not the presence of other cardiovascular risk factors, were associated to with a greater percentage use of a BPLD and a LLD.
Conclusion: A population survey followed by a letter of intervention to both the patient and GP are effective to improve the use of blood pressure and lipid lowering drugs as a primary prevention in patients with hypertension and hyperlipidemia. Our therapeutic advice however, was followed only in about one of the three subjects with hypertension and one of the four subjects with hyperlipidemia. The levels of blood pressure and plasma total cholesterol are important variables influencing the GP to prescribe a BPLD and/or LLD.