Antibiotic prophylaxis against infective endocarditis: new guidelines, new controversy?

For over 50 years cardiologists have routinely recommended antibiotic prophylaxis (ABP) at the time of dental procedures in patients deemed to be at risk of infective endocarditis (IE). Reviews and editorials all acknowledged the lack of robust evidence for effectiveness of ABP and from time to time the literature has been reviewed and expert opinion synthesised into guidelines. In the UK, the 2004 Joint Royal College of Physicians/British Cardiac Society guideline has been widely followed.1 In 2006 new guidelines were published by the British Society for Antimicrobial Chemotherapy (BSAC).2 These guidelines were important because this committee’s recommendations are incorporated into the British National Formulary. The BSAC guidelines recommended withdrawal of ABP for the majority of patients limiting them to individuals perceived to be at the highest risk of IE (e.g. a prior history of IE, prosthetic cardiac valves and surgically constructed pulmonary or system shunts/conduits). These guidelines were welcomed by the majority of dentists and microbiologists as a step in the right direction. However, many cardiologists, who had seen first-hand the horrors of IE, did not wish to see the rejection of a therapy that was thought by most to be effective and harmless. The lack of agreement between the medical and dental professions resulted in the issue being referred to the National Institute for Health and Clinical Excellence (NICE) for an authoritative statement.3

NICE guidance

The NICE review tried to determine which cardiac conditions are associated with increased risk of IE; whether dental treatment is associated with acute risk of developing the condition and whether ABP was effective in prevention of cases and deaths. The NICE guideline concluded that patients with structural heart disease were at increased risk of IE but did not find convincing evidence that dental ABP was cost-effective. They calculated that if amoxicillin prophylaxis was effective then the cost of preventing a single case of IE would be circa £12 million. In the absence of high-quality evidence for clinical effectiveness they recommended that routine dental ABP should be abandoned.

The methodology employed by NICE was robust and transparent, in contrast to the evidence supporting ABP. The NICE guidelines development group usually review therapies supported by data from mega-trials and meta-analyses, however, the literature on ABP is more like the Dead Sea scrolls – fragmented, imperfect, subject to various interpretations and mainly missing. In this situation there is a strong reliance on expert opinion and many would agree that absence of evidence should not be regarded as evidence of absence. The poor quality of the supportive data and reliance on expert opinion probably explains the differences between the BSAC and American Heart Association/American College of Cardiology (AHA/ACC) guidelines and those of NICE. The NICE guideline development process is transparent and the comments from stakeholders are published. Review of these comments shows that the dental community is generally in favour of the new recommendations, which reinforce the link between good overall dental hygiene and prevention of IE rather than relying on ABP just at the time of dental work. Other stakeholders are concerned not only with the guideline itself but potential difficulties with implementation. In this respect the Department of Health stated that the guidelines were a “very significant shift in current clinical practice … we feel there is a serious risk of confusion and lack of compliance”.

Reaction

The reaction to these guidelines has been predictable. Many cardiologists see them as a step too far and question the credibility of a guideline that is based around the re-evaluation of weak historical evidence rather than high-quality clinical trials. To many cardiologists the case supporting ABP is simple: IE is a very serious disease with a high mortality and morbidity; decades of clinical experience have illustrated that certain patients are at increased risk; dental work is associated with bacteriaemia and antibiotics kill bacteria cheaply, effectively and with low toxicity. Most cardiologists acknowledge the lack of definitive evidence for effectiveness but believe that even if ABP prevents only a minority of IE, surely this is preferable. It is for these reasons we believe that most cardiologist are uneasy about the new guidelines. Of course we may never be able to measure the precise effectiveness of ABP and this uncertainty was acknowledged more than 25 years ago by Celia Oakley and Walter Somerville who hypothesised at least four reasons why ABP might fail:⁴

• Perhaps it was not given.
• Perhaps it was not given to the right people.
• Perhaps it does not work.
• Perhaps it is irrelevant.

Now that the guideline has been published various scenarios and difficulties may be envisaged. For example, if a cardiologist continues to recommend ABP for a patient but the dentist wants to follow the NICE guidelines. Each clinician has a separate duty of care to the patient and both may feel they are acting within the patient’s best interest. While the view expressed by the cardiologist is a valid consideration, legally it is not definitive and would only be taken as part of the overall ‘mix’ of information. The Dental Protection organisation has already advised their members that if a cardiologist continues to recommend ABP it is inadvisable, as it conflicts with guidelines issued by an authoritative body; this recommendation holds even if it has been confirmed in writing by the cardiologist.⁵

The art of medicine

A survey of cardiologists, prior to the publication of the NICE guidelines, showed that 94% felt that patients with moderate risk of IE should receive ABP and 96% believed that it was unsafe not to recommend ABP to such patients prior to dental treatment.⁶ With such overwhelming support for the status quo what is the legal position of the cardiologist who decides to act against the guideline? The Bolam defence stated that a doctor is not guilty of negligence if “he has acted in accordance with a practice accepted as proper by a responsible body of medical men skilled in that particular art”.⁷ Since NICE is a national body appointed by statute it is likely to be regarded as a responsible body. Although NICE guidelines are not enforceable in law the threat of legal action might lead cardiologists, while not agreeing with the guidelines, to comply with them since any potential legal action could be robustly defended. However, compliance with guidelines due to a fear of litigation could, in time, weaken the Bolam defence due to a lack of variation in practice. Over 2,000 years ago, Plato explored the difference between skills grounded in practical expertise and those based solely on following instructions or obeying rules. He argued that once the medical profession dedicates itself to the provision of healthcare through guidelines it is committed to continue observing them because, at that point, the expertise resides within the guidelines rather than the clinician. Once this occurs then any guideline deviation is unjustifiable on the basis of clinical judgement.

In clinical cardiology we are used to facing decisions where the clinical evidence base does not completely apply to the particular patient at hand. In this situation we give an opinion – a belief based not on positive knowledge but on what seems valid, true, or probable to one’s own mind. It is time for cardiologists to do that with ABP. If we believe, as a group, that NICE has gone too far in recommending the abolition of ABP then we should act together as a responsible body of doctors robustly defending the Bolam principle and our right to clinical judgement.

Conflict of interest

None declared.

References

1. Ramsdale DR, Turner-Stokes L. Prophylaxis and treatment of infective endocarditis in adults: a concise guide. Clin Med 2004;4:545–50.
2. Gould FK, Elliott TS, Foweraker J et al. Guidelines for the prevention of endocarditis: report of the Working Party of the British Society for Antimicrobial Chemotherapy. J Antimicrob Chemother2006;57:1035–42.
3. National Institute for Health and Clinical Excellence. Prophylaxis against infective endocarditis: NICE guidance. London: NICE, 2008. Available from: http://www.nice.org.uk/Guidance/CG64
4. Oakley C, Somerville W. Prevention of endocarditis. Br Heart J 1981;45:233–5.
5. Dental Protection. Antibiotic cover for dental procedures – frequently asked questions. Available from: http://www.dentalprotection.org/assets/documents/2008_DPL_FAQ_Antibiotic_Prophylaxis_0308.pdf
6. Ramsdale DR, Egred M, Palmer ND, Chalmers JAC. Antibiotic prophylaxis to prevent infective endocarditis should be given to patients. Heart 2007;eletter. Available from: http://heart.bmj.com/cgi/eletters/93/6/753-a#1477
7. Bolam v Friern Hospital Management Committee 1957. Available from: http://oxcheps.new.ox.ac.uk/casebook/Resources/BOLAMV_1%20DOC.pdf