Patterns of analgesic utilisation among people with knee osteoarthritis: a cohort study using UK primary care data.

Background: Osteoarthritis (OA) is a prevalent disabling joint disease affecting more than 300 million people globally and knees are most commonly affected. It is associated with pain and functional limitation that adversely affect mental well-being and compromise quality of life. Analgesic use is common among patients with knee osteoarthritis (KOA), however, data on patterns of analgesics use at an individual patient level are sparse. The present study describes patterns of analgesic use, by determining the proportion of persistent users within one year of therapy initiation in patients with KOA. Methods: A retrospective cohort study using the clinical practice research datalink. Analgesic prescriptions for adults with an incident KOA diagnosis were captured and grouped into five exposure groups including: antidepressants, antiepileptic drugs (AEDs), opioids, non-steroidal anti-inflammatory drugs (NSAIDs) and paracetamol. A persistent user was a person who used >180 defined daily doses (DDDs) per year and had prescriptions in at least three out of the four quarters of the year. Results: Variable proportions of patients used respective analgesic classes persistently during the first year after prescribing; 36.8% of antidepressant users, 27.0% of NSAIDs, 23.8% of AEDs, 17.5% of paracetamol and 14.9% of opioid users were persistent users. Across classes, persistent users were slightly younger, were issued more prescriptions and used higher doses of analgesics compared to non-persistent users. Conclusion: Between 14.9% and 36.8% became persistent analgesic users by the end of the first year after their initial prescription. The study applied meaningful clinical attributes to define persistence. This informs future research on clinical and adverse drug outcomes in persistent users compared to non-persistent users across five separate analgesic classes.