Introducing a drug formulary to general practice--effects on practice prescribing costs.

A drug formulary comprising 249 preparations of 132 drugs and drug combinations was prepared by the partners in a three-doctor general practice serving more than 5000 patients. No attempt was made to change to generic prescribing nor were repeat prescription drugs altered. Introduction of the formulary in September 1981 was followed by an increase in the proportion of prescriptions containing drugs from the formulary from about 55% to more than 60% for both repeat and non-repeat prescriptions. The proportion of formulary drugs on non-repeat prescriptions reached a maximum of 78% within the first year with the additional influence of information feedback. Over the first year the level of formulary drugs used for both repeat and nonrepeat prescribing levelled off at about 62%. Even with these modest changes, when compared with the costs of general practice prescribing in Scotland as a whole, the introduction of the formulary resulted in savings of approximately 10% within the practice for the mean ingredient costs both per patient and per prescription.