OBJECTIVE: At the beginning of the COVID-19 pandemic in the Netherlands, the Dutch Working Party on Antibiotic Policy constructed an advisory document about off-label drug treatment options that was regularly updated with new scientific findings. The aim of this study is to describe the dynamics in applied COVID-19 pharmacotherapy during the first 100 days of the pandemic and to assess how the national advisory document influenced local hospital policies. METHODS: A multicentre observational cohort study was conducted in six hospitals in the Netherlands. Patients with confirmed COVID-19 admitted between 27 February and 7 June 2020 were studied. Drug prescription data were collected and percentages of patients receiving a specific treatment were calculated. These percentages were plotted together with release dates of the national advisory document. Semi-structured in-depth interviews with hospital pharmacists and infectious diseases specialists were conducted to gain insight into the development and implementation of pharmacotherapy treatment protocols in hospitals. RESULTS: Data from 1511 patients (60% men, mean age 66 years) were analysed. From mid-March (hydroxy)chloroquine was being prescribed in all six hospitals to approximately 70% of patients at admission. Frequencies of other off-label treatments were below 2%. In the week of 6 April 2020, the first hospital discontinued prescribing (hydroxy)chloroquine and the last hospital discontinued in the week of 4 May 2020 (total range -19 to +10 days after the national advisory document advised against its use (1 May 2020)). All interviewees (n=6) stated that the hospitals based their policies mainly on the national advisory document but also assessed scientific literature themselves. Order panels were constructed to support prescribing. CONCLUSION: Dutch hospitals opted en masse for (hydroxy)chloroquine as COVID-19 therapy at the start of the pandemic, although the time until the therapy was no longer prescribed differed by several weeks. The fact that ...