A multi-centre open-label two-arm randomised superiority clinical trial of azithromycin versus usual care in ambulatory COVID-19: study protocol for the ATOMIC2 trial

Trials. 2020 Aug 17;21(1):718. doi: 10.1186/s13063-020-04593-8.


Background: Azithromycin is an orally active synthetic macrolide antibiotic with a wide range of anti-bacterial, anti-inflammatory and antiviral properties. It is a safe, inexpensive, generic licenced drug available worldwide and manufactured to scale and is a potential candidate therapy for pandemic coronavirus disease 2019 (COVID-19). Azithromycin was widely used to treat severe SARS-CoV and MERS-CoV, but to date, no randomised data are available in any coronavirus infections. Other ongoing trials are exploring short courses of azithromycin either in early disease, within the first 7 days of symptoms, when azithromycin's antiviral properties may be important, or late in disease when anti-bacterial properties may reduce the risk of secondary bacterial infection. However, the molecule's anti-inflammatory properties, including suppression of pulmonary macrophage-derived pro-inflammatory cytokines such as interleukins-1β, -6, -8, and -18 and cytokines G-CSF and GM-CSF may provide a distinct therapeutic benefit if given in as a prolonged course during the period of progression from moderate to severe disease.

Methods: ATOMIC2 is a phase II/III, multi-centre, prospective, open-label, two-arm randomised superiority clinical trial of azithromycin versus standard care for adults presenting to hospital with COVID-19 symptoms who are not admitted at initial presentation. We will enrol adults, ≥ 18 years of age assessed in acute hospitals in the UK with clinical diagnosis of COVID-19 infection where management on an ambulatory care pathway is deemed appropriate. Participants will be randomised in a 1:1 ratio to usual care or to azithromycin 500 mg orally daily for 14 days with telephone follow-up at days 14 and 28. The primary objective is to compare the proportion with either death or respiratory failure requiring invasive or non-invasive mechanical ventilation over 28 days from randomisation. Secondary objectives include mortality/respiratory failure in those with a PCR-confirmed diagnosis; all-cause mortality; progression to pneumonia; progression to severe pneumonia; peak severity of illness and mechanistic analysis of blood and nasal biomarkers.

Discussion: This trial will determine the clinical utility of azithromycin in patients with moderately severe, clinically diagnosed COVID-19 and could be rapidly applicable worldwide.

Trial registration: ClinicalTrials.gov NCT04381962 . Registered on 11 May 2020. EudraCT identifier 2020-001740-26 . Opened for accrual on 29 May 2020.

Keywords: Azithromycin; COVID-19; Coronavirus; Macrolide; Mortality; Randomised controlled trial; Respiratory failure; SAR-CoV-2; Trial.

Publication types

  • Clinical Trial Protocol
  • Clinical Trial, Phase II
  • Clinical Trial, Phase III
  • Comparative Study
  • Multicenter Study

MeSH terms

  • Anti-Bacterial Agents / therapeutic use*
  • Azithromycin / therapeutic use*
  • Betacoronavirus*
  • COVID-19
  • Coronavirus Infections / drug therapy*
  • Humans
  • Pandemics
  • Pneumonia, Viral / drug therapy*
  • Prospective Studies
  • Randomized Controlled Trials as Topic*
  • Research Design
  • SARS-CoV-2
  • Severity of Illness Index


  • Anti-Bacterial Agents
  • Azithromycin

Supplementary concepts

  • COVID-19 drug treatment

Associated data

  • ClinicalTrials.gov/NCT04381962