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

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.