The antibiotics azithromycin and doxycycline will no longer be given to patients in a Covid treatment trial after researchers found they were ‘not generally effective’.

The Oxford University PRINCIPLE trial concluded ‘neither treatment reduces the time taken for people to first report that they feel recovered sufficiently to achieve meaningful clinical benefit’.

Also, neither of the antibiotics proved to significantly reduce hospital admissions or deaths compared with the care usually provided by clinicians.

Existing clinical guidance in England currently recommends treatment with oral doxycycline for suspected pneumonia in people with Covid-19 in the community if the cause is bacterial, or if it is unclear whether the cause is bacterial or viral and symptoms are particularly concerning.

But the PRINCIPLE trial has found that the drug is not effective as a treatment for suspected Covid-19 in the absence of bacterial pneumonia, and researchers warned it ‘should not be used in this way’.

The trial is a nationwide study testing the effectiveness of therapies available in primary care to potentially speed up the recovery of Covid patients and prevent hospital admission.

An inhaler - budesonide - is the only drug which currently remains part of the study, after hydroxychloroquine was suspended in June.

Professor Richard Hobbs, head of the University of Oxford’s Nuffield Department of Primary Care Health Sciences and co-lead of the PRINCIPLE trial, said: ‘While it is disappointing that neither azithromycin nor doxycycline speed-up recovery for those with Covid-19 in the community, these are both important findings which will reduce the use of ineffective antibiotics for this illness.

‘This finding shows the importance of doing rigorous clinical trials in real-world settings before treatments are rolled out on a wide scale. Widespread use of treatment should not be based on laboratory studies and opinion alone.

Professor Chris Butler, another co-lead on the trial. said: ‘These are two important findings, as both azithromycin and doxycycline have been used for treating Covid-19 in the community even in the absence of suspected bacterial pneumonia, so this practice should now be re-considered - particularly because overuse of antibiotics in the community can fuel the emergence of antimicrobial resistance.

‘PRINCIPLE is one of the first trials to report about doxycycline for Covid-19 worldwide, and as this drug is in common use for this condition, this should help guide prescribing decisions for Covid-19.’