PRINCIPLE: a community-based COVID-19 platform trial
Authors: John Macleod, John Norrie
Journal: The Lancet Respiratory Medicine (2021)

As COVID-19 evolved in early 2020, several crucial issues for public health became apparent, including the need to reduce pressure on secondary care through effective treatment in the community for those at highest risk of hospital admission. PRINCIPLE, which began in April, 2020, was designed to test multiple therapeutic candidates efficiently using a master protocol within a platform trial.1Park JJH Siden E Zoratti MJ et al.Systematic review of basket trials, umbrella trials, and platform trials: a landscape analysis of master protocols.Trials. 2019; 20: 572Crossref PubMed Scopus (208) Google Scholar, 2LaVange L Adam SJ Currier JS et al.Accelerating COVID-19 therapeutic interventions and vaccines (ACTIV): designing master protocols for evaluation of candidate COVID-19 therapeutics.Ann Intern Med. 2021; (published online June 29.)https://doi.org/10.7326/M21-1269Crossref PubMed Scopus (23) Google Scholar In The Lancet Respiratory Medicine, Christopher Butler and colleagues3Butler CC Yu L-M Dorward J et al.Doxycycline for community treatment of suspected COVID-19 in people at high risk of adverse outcomes in the UK (PRINCIPLE): a randomised, controlled, open-label, adaptive platform trial.Lancet Respir Med. 2021; (published online July 27.)https://doi.org/10.1016/S2213-2600(21)00310-6PubMed Google Scholar report the findings of one of the possible treatments for COVID-19; a relatively cheap and safe antibiotic doxycycline, for which community prescribing increased early in the pandemic.4Zhu N Aylin P Rawson T Gilchrist M Majeed A Holmes A Investigating the impact of COVID-19 on primary care antibiotic prescribing in north west London across two epidemic waves.Clin Microbiol Infect. 2021; 27: 762-768Summary Full Text Full Text PDF PubMed Scopus (54) Google Scholar This trial aimed to assess the efficacy of doxycycline to treat suspected COVID-19 in the community among people at high risk of adverse outcomes. As antibiotic prescribing promotes antimicrobial resistance, it was imperative to quickly establish if increased doxycycline exposure in the population was offset by realisable benefits. Designing and implementing randomised trials in pandemics is challenging, due to delays in initiation, and difficulties in finding locations with prevalent virus. A platform design offers the possibility of finding safe and effective interventions quickly. Given the inevitable uncertainties in the design (in population, intervention, control, and outcomes), flexibility is needed, which PRINCIPLE achieved admirably. With regards to population, recruitment to community-based COVID-19 studies is notoriously hard; in PRINCIPLE, an adaptive recruitment strategy generated 25% of participants from more than 200 general practices, with the remainder from online self-referral, to whom study medication was delivered by courier. An additional challenge in this trial was pandemic service disruption; from November, 2020, further adaptions included enrolling high-risk individuals with positive test results independent of contact with their general practitioner.5Beckman J Smith A PRINCIPLE—accelerated recruitment for clinical trials through rapid access to large, linked datasets and integrated patient engagement.https://www.hdruk.ac.uk/case-studies/accelerated-recruitment-for-clinical-trials-through-rapid-access-to-large-linked-datasets-and-integrated-patient-engagement/Date: April 1, 2021Date accessed: July 15, 2021Google Scholar In December, 2020, recruitment to the doxycycline group was stopped, having met the criteria for statistical futility. The intervention was not adapted, and there was high compliance with doxycycline (82·2% of participants self-reported taking doxycycline for at least 6 days). There is some controversy around control groups in platform trials,6Dodd LE Freidlin B Korn EL Platform trials—beware the noncomparable control group.N Engl J Med. 2021; 384: 1572-1573Crossref PubMed Scopus (49) Google Scholar as controls and participants in intervention groups might not have been contemporaneously randomised. Here, the control was usual care only; PRINCIPLE opened on April 2, 2020, but randomisation to the doxycycline group only began on July 24, 2020. However, the authors adjusted for any potential temporal drift directly using Bayesian regression modelling, and by doing a sensitivity analysis in only those who were contemporaneously randomly assigned (ie, all participants who were randomly assigned to usual care plus doxycycline or usual care only during the time period when the usual care plus doxycycline group was open to randomisation), and findings were robust. The primary outcome was changed—a major step—from COVID-19-related hospitalisations or deaths to time to self-reported recovery, as the early observed numbers of hospitalisations and deaths indicated that 1500 participants per group would be required for adequate power to show even a large difference. This change was made then for good reason, and before any interim analyses were done. Somewhat strangely, the underpowered original primary outcome was retained as a coprimary outcome, but by using a gate-keeping approach no power was wasted. The study also used response adaptive randomisation, and allocated more participants to treatments that seemed to be working as the trial progressed. This approach is controversial;7Begg CB Ethical concerns about adaptive randomization.Clin Trials. 2015; 12: 101Crossref PubMed Scopus (9) Google Scholar however, in this trial where doxycycline was shown to be ineffective (median time to first self-reported recovery 9·6 days [95% Bayesian Credible Interval (BCI) 8·3–11·0] in the usual care plus doxycycline group vs 10·1 days [8·7–11·7] in the usual care only group, hazard ratio 1·04 [95% BCI 0·93–1·17]), adaptive randomisation has marginal influence on randomisation allocation ratios. The UK Department of Health and Social Care general practice treatment advice changed in January, 2021, on the basis of these results, and doxycycline is now only recommended in patients with evidence for bacterial co-infection, which appears to be relatively uncommon in COVID-19.8Robinson J Azithromycin and doxycycline should not be used in the management of COVID-19, DHSC advises.https://pharmaceutical-journal.com/article/news/azithromycin-and-doxycycline-should-not-be-used-in-the-management-of-covid-19-dhsc-advisesDate: Feb 1, 2021Date accessed: July 15, 2021Google Scholar The effect of this change on general practitioner prescribing behaviour will be interesting to examine. A key question that remains is how secure is the conclusion that doxycycline is ineffective? As microbiological confirmation of SARS-CoV-2 infection was not obtained for many participants in PRINCIPLE, some individuals might have been misclassified as having COVID-19, which could reduce power. The assumed treatment effects were large; however, the 95% BCI on the revised primary outcome ruled out a benefit of more than 17% improvement. The dose of doxycycline might have been inadequate. Furthermore, treatment was started up to 14 days after symptom onset, which might have obscured evidence for effective early treatment. During PRINCIPLE, as a recommended COVID-19 treatment, doxycycline was widely prescribed in the general population, which might have led to dilution of any treatment effect. The scarcity of microbiological confirmation of infection and imperfect testing in those tested is the reality of most community treatment of infection. Any suggestion of a possible benefit from doxycycline in patients with positive tests should be seen in this context. In-vitro evidence suggesting possible effectiveness of doxycycline against SARS-CoV-2 also suggested that the treatment regime tested in PRINCIPLE was appropriate.9Gendrot M Andreani J Jardot P et al.In vitro antiviral activity of doxycycline against SARS-CoV-2.Molecules. 2020; 255064Crossref PubMed Scopus (55) Google Scholar Results of experimental treatment evaluations often show potential that is not realised in real-world settings. These findings from PRINCIPLE, which provide no evidence of benefit of doxycycline in the community management of COVID-19 patients at high risk of adverse outcomes, should likewise be seen in this context. This pragmatic trial10Ford I Norrie J Pragmatic trials.N Engl J Med. 2016; 375: 454-463Crossref PubMed Scopus (871) Google Scholar—with few exclusion criteria, inclusion of patients with suspected COVID-19 who did not necessarily have a positive PCR result, and no placebo or blinding—estimated real-world effectiveness, not idealised efficacy. PRINCIPLE included sensitivity and subgroup analyses in participants with positive PCR confirmation of infection and by duration of illness before randomisation, neither of which showed any meaningful effect. Whether doxycycline might work, and at what dose and duration, could still be investigated in early-phase efficacy studies in future waves of the SARS-CoV-2 pandemic. The findings reported by Butler and colleagues strongly suggest that doxycycline is not effective in reducing symptom duration or COVID-19-related hospitalisations or deaths in patients with COVID-19 who are at high risk of adverse outcomes. PRINCIPLE has shown it is possible to produce robust evidence from a randomised trial for interventions in community settings during a pandemic, by using a pragmatic platform effectiveness design that was flexibly and skilfully implemented. The PRINCIPLE design should be studied carefully, for future deployment when needed. JN declares he is Chair of the Medical Research Council and National Institute for Health Research (NIHR) Efficacy and Mechanisms Evaluation funding panel; NIHR funded the PRINCIPLE study. JN had no involvement in any aspect of the PRINCIPLE study. JM declares no competing interests. Doxycycline for community treatment of suspected COVID-19 in people at high risk of adverse outcomes in the UK (PRINCIPLE): a randomised, controlled, open-label, adaptive platform trialIn patients with suspected COVID-19 in the community in the UK, who were at high risk of adverse outcomes, treatment with doxycycline was not associated with clinically meaningful reductions in time to recovery or hospital admissions or deaths related to COVID-19, and should not be used as a routine treatment for COVID-19. Full-Text PDF