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

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posted on 2021-04-01, 13:40 authored by Chiamaka Chiedozie, Mark Murphy, Tom FaheyTom Fahey, Frank MoriartyFrank Moriarty

Aim: To apply the drug utilisation 90% (DU90%) indicator (the number of unique drugs which makes up 90% of a doctor's prescribing) to general practitioner (GP) practices prescribing in England to examine time trends, practice-level variation, and relationships with practice characteristics, prescribing costs and low-value prescribing.

Study design: Retrospective cohort study.

Setting: Primary care in England, using publicly available prescribing data available from the National Health Service (NHS) digital platform for 2013-2017.

Participants: All general practices in England (n=7620).

Primary and secondary outcome measures: The DU90% was calculated on an annual basis for each practice based on medication British National Formulary codes. Low-value prescribing was defined using NHS 2017 guidance (including lidocaine plasters, liothyronine, omega-3 supplements). Descriptive statistics were generated per year on time trends and practice-level variation in the DU90%. Multilevel linear regression was used to examine the practice characteristics (relating to staff, patients and deprivation of the practice area).

Results: Among 7620 practices, mean DU90% ranged from 130.0 to 131.0 across study years, and regarding variation between practices, there was 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 women or aged ≥45 years, higher number of GPs working in the practice and being in a more deprived area were associated with a higher DU90%. Practices in higher quintiles of DU90% had higher levels of low-priority prescribing and prescribing costs.

Conclusion: GP practices typically use 130 different medications in the bulk of their prescribing. Higher DU90% was associated with higher levels of low-priority prescribing and prescribing costs. Increasing use of personal formularies may enhance prescribing quality and reduce costs.


Health Research Board in Ireland (HRB) through the Summer Student Scholarships (grant no. SS/2018/080)

HRB Centre for Primary Care Research (HRC/2014/01)

Royal College of Surgeons in Ireland Undergraduate Research Summer School.


Associated research data files

The data that support the findings of this study are openly available in Zenodo at https://doi.org/10.5281/zenodo.3894539


The original article is available at https://bmjopen.bmj.com Pre-print is available on medRxiv, https://doi.org/10.1101/2020.06.16.20132654 and RCSI repository https://hdl.handle.net/10779/rcsi.14939058.v1

Published Citation

Chiedozie C, Murphy ME, Fahey T, Moriarty F. How many medications do doctors in primary care use? An observational study of the DU90% indicator in primary care in England. BMJ Open. 2021;11(3):e043049.

Publication Date

5 February 2021

PubMed ID



  • HRB Centre for Primary Care Research
  • School of Pharmacy and Biomolecular Sciences
  • Undergraduate Research
  • General Practice

Research Area

  • Endocrinology
  • Health Professions Education
  • Population Health and Health Services


BMJ Publishing Group Ltd


  • Published Version (Version of Record)