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Background Since COVID-19 was first recognised, there has been ever-changing evidence and misinformation around effective use of medicines. Understanding how pandemics impact on medicine use can help policymakers act quickly to prevent harm. We quantified changes in dispensing of common medicines proposed for "re-purposing"due to their perceived benefits as therapeutic or preventive for COVID-19 in Australia. Methods We performed an interrupted time series analysis and cross-sectional study using nationwide dispensing claims data (January 2017-November 2020). We focused on six subsidized medicines proposed for re-purposing: hydroxychloroquine, azithromycin, ivermectin, colchicine, corticosteroids, and calcitriol (Vitamin D analog). We quantified changes in monthly dispensing and initiation trends during COVID-19 (March-November 2020) using autoregressive integrated moving average models and compared characteristics of initiators in 2020 and 2019. Results In March 2020, we observed a 99% (95%CI: 96%-103%) increase in hydroxychloroquine dispensing (approximately 22% attributable to new users), and a 199% increase (95%CI: 184%-213%) in initiation, with an increase in prescribing by general practitioners (42% in 2020 vs 25% in 2019) rather than specialists. These increases subsided following regulatory restrictions on prescribing. There was a small but sustained increase in ivermectin dispensing over multiple months, with an 80% (95%CI 42%-118%) increase in initiation in May 2020 following its first identification as potentially disease-modifying in April. Other than increases in March related to stockpiling, we observed no change in the initiation of calcitriol or colchicine during COVID-19. Dispensing of corticosteroids and azithromycin was lower than expected from April through November 2020. Conclusions While most increases in dispensing observed early on during COVID-19 were temporary and appear to be related to stockpiling among existing users, we observed increases in the initiation of hydroxychloroquine and ivermectin and a shift in prescribing patterns which may be related to the media hype around these medicines. A quick response by regulators can help limit inappropriate repurposing to lessen the impact on medicine supply and patient harm.

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