Background: Reducing inappropriate antibiotic prescribing in primary care is a public health priority. Objectives: We hypothesized that a subset of patients account for the majority of antibiotic prescriptions in primary care. We investigated the relationship between the total amount of antibiotics prescribed, individual-level antibiotic use and comorbidity. Methods: This was a cohort study using electronic health records from 1 948 390 adults registered with 385 primary care practices in the UK in 2011–13. We estimated the average number of antibiotic prescriptions per patient and the association between prescribing and comorbidity. We modelled the impact on total prescribing of reducing antibiotic use in those prescribed antibiotics most frequently. Results: On average 30.1% (586 194/1 948 390) of patients were prescribed at least one antibiotic per year. Nine percent (174 602/1 948 390) of patients were prescribed 53% (2 091 496/3 922 732) of the total amount of antibiotics, each of whom received at least five antibiotic prescriptions over 3 years. The presence of any comorbidity increased the prescribing rate by 44% [adjusted incidence rate ratio (IRR) 1.44, 95% CI 1.43–1.45]; rates of prescribing to women exceeded those in men by 62% (adjusted IRR 1.62, 95% CI 1.62–1.63). Conclusions: Half of antibiotics prescribed to adults in primary care were for <10% of patients. Efforts to tackle antimicrobial resistance should consider the impact of this on total prescribing.

Olanzapine is more commonly prescribed to people with lower weight. However, after accounting for baseline weight, age, sex and diagnosis, olanzapine is still associated with greater weight gain over two years than risperidone or quetiapine. Baseline weight does not ameliorate the risks of weight gain associated with antipsychotic medication. Weight gain should be assertively discussed and managed for people prescribed antipsychotics, especially olanzapine.