Objective. To study trends and variation in adherence to the main national formulary for the 20 most prevalent health problems in Dutch general practice over a 5-year period (2003–07).
Methods. Routine electronic medical records from a pool of 115 representative general practices were linked to the main national formulary. Analyses included over 2 million prescriptions for 246 391 patients. The outcome variable was whether or not the prescribed medication was congruent with recommendations in the national formulary. Trends and variation were analysed using three-level multilevel logistic regression analyses (general practice, patient, and prescription).
Results. The percentage of formulary adherent prescriptions for the 20 most prevalent health problems was 73–76% between 2003 and 2007. The percentage varied considerably between guidelines. Lowest adherence rates were found for acute bronchitis and acute upper respiratory infection. Interpractice variation was constant over time.
Conclusions. General practice information networks are useful for monitoring general patterns of formulary on a year-to-year basis. Formulary adherence is stable over time but varies across diagnoses, patients and general practices. In the past decade, efforts have been made to increase the level of formulary adherent prescribing. These general efforts managed to stabilize (variation in) adherence in a field where many other initiatives (e.g. by pharmaceutical companies) are undertaken to influence prescribing behaviour.