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A selection of medical pills.

A study to examine whether care home patients experience health benefits, such as reduced infections, from taking a daily probiotic supplement.


It is known that older people living in care homes are prescribed far more antibiotics than the general population because of the higher number of infections they have, caused by weakened immunity, close-proximity living and co-existing health conditions.

The cost of chronic antibiotic use

High antibiotic use increases the risk of antibiotic resistance in care homes that can spread within care homes and to hospitals and the community. Infections in care home residents cost the NHS more than £54 million a year in hospitalisation alone, and infections are the commonest reason for residents to be hospitalised. Reduction in antibiotic use and antibiotic resistance could improve residents’ quality of life, save money, and help preserve the usefulness of existing antibiotics. There is an urgent need to reduce antibiotic resistance through infection prevention in care homes.

Potential benefits of probiotics

Probiotics are live bacteria that may confer health benefits by improving immune function and reducing carriage of potentially harmful bacteria. Probiotics are safe and cheap and are widely available as supplements. However, research involving their effectiveness in care home residents is currently lacking.

Other than vaccination and good hygiene, there are few proven ways to prevent infections in older care home residents - so they represent an important target in efforts to combat antibiotic resistance. Our study should answer the question whether or not daily probiotics prevent infections.

Professor Chris Butler, Chief investigator PRINCESS study, University of Oxford

PRINCESS will be the first rigorous randomised controlled trial of daily probiotic versus placebo probiotic over 12 months on antibiotic administration for infections.

Study design

The trial is designed to focus on antibiotic use for all care home residents - including those lacking mental capacity and who are most frail. Previous studies in care home populations, including a recent study carried out by the same research team (PAAD Study), showed that 72% of care home residents lacked mental capacity to consent for themselves. Evidence shows that those lacking capacity are likely to be more frail than those with capacity, and have an increased vulnerability to infection, and so are more likely to benefit from any reduction in infections and subsequent requirement for antibiotics.

Recruitment targets

We aim to recruit 330 residents from care homes in Wales and England to take part in an individually randomised trial of a probiotic preparation vs. placebo preparation, and follow them up for 12 months. The aim is to trial the probiotic preparation (containing Lactobacillus rhamnosus, LGG and Bifidobacterium animalis subsp. lactis, BB-12) to determine whether this product prevents infections over a 12 month period in older people living in care homes.

Measuring probiotic effectiveness

Trial participants will take a once daily dose of study product for 12 months, taken as a capsule or sprinkled on food. They will be asked to provide (optional) blood, saliva and stool samples at the start of the study, and three and 12 months later. Participants will also complete questionnaires either by themselves or with the help of someone else.

We will assess total days on antibiotics for infections, including respiratory, urinary tract, skin and gastro-intestinal infection, and other measures such as changes in immune response to influenza vaccination.

Involving the public and patients

Public and patient involvement has greatly benefitted the trial. Two members of the public have been recruited through Involving People (Wales) to advise the research team throughout the whole life-cycle of the trial. Additional lay members form part of the independent committee overseeing the trial.

Their invaluable involvement in the initial planning and design of PRINCESS, and ongoing involvement during the trial itself, will maximise the quality of the research and ensure that the study is feasible and relevant. Ultimately, it is hoped that involving members of the public will have a positive impact on ensuring the trial findings improve outcomes for older people living in care homes.

Research impact

Other than vaccination and hygiene methods, there are few interventions proven to prevent infection in care home residents. The trial will provide information on a safe and widely accessible intervention for the prevention of infection, antibiotic use and antibiotic resistance in care home residents.

The results will help care home residents, and those caring for them, to make evidence based decisions either to take or not take this probiotic product in order to maintain their optimal health and wellbeing.

Funder: National Institute for Health Research Efficacy and Mechanism Evaluation (NIHR-EME) Programme

Chief Investigator: Professor Chris Butler