How many medications do doctors in primary care use? An observational study of the DU90% indicator in primary care in England.

Abstract

Aim: To apply the DU90% indicator (the number of unique drugs which make up 90% of a doctor's prescribing) to GP practices prescribing in England to examine time trends, practice-level variation, and relationships with practice characteristics Method: This is an observational cohort study of all general practices in England. It utilises publicly available prescribing data from the National Health Service (NHS) Digital platform for 2013-2017. The DU90% was calculated on an annual basis for each practice based on medication BNF codes. Descriptive statistics were generated per year on time trends and practice-level variation in the DU90%. Multi-level linear regression was used to examine the practice characteristics (relating to staff, patients, and deprivation of the practice area). Results: A total of 7,623 GP practices were included. The mean DU90% ranged from 130.1 to 133.4 across study years, and variation between practices was low (with a 1.4 fold difference between the lowest and highest 5% of practices). A range of medications were included in the DU90% of virtually all practices, including atorvastatin, levothyroxine, omeprazole, ramipril, amlodipine, simvastatin and aspirin. A higher volume of prescribing was associated with a lower DU90%, while having more patients, higher proportions of patients who are female or aged 65+, higher number of GPs working in the practice, and being in a more deprived area were associated with a higher DU90%. Conclusion: GP practices typically use 130 different medications in the bulk of their prescribing. Increasing use of personal formularies may enhance prescribing quality and reduce costs.