On Jan. 25, 2021, scientists at the University of Oxford reported that after reviewing interim analyses of both the azithromycin and doxycycline arms of the PRINCIPLE trial, the independent Trial Steering Committee advised the trial investigators, who concluded that there was no beneficial effect in patients aged over 50 who are treated with either antibiotic at home in the early stages of COVID-19.

Azithromycin and doxycycline are two commonly used antibiotics investigated as separate treatments in the trial.