**1. Historical perspectives**

In 1955, the American Heart Association (AHA) was the first medical society to establish the need for a prophylactic antibiotic regimen to prevent infective endocarditis (IE) in at-risk patients undergoing various surgical procedures, including tooth extractions and other dental manipulations that affect the gum.

In the pre-antibiotic era, reports based on clinical observations described cases of IE of streptococcal aetiology in which there was a history of professional dental manipulation. This suggested the possibility that "transient bacteraemia during dental procedures may lead to subacute endocarditis in subjects with abnormal heart valves" [1].

The 1955 AHA Committee on the Prevention of Rheumatic Fever and Bacterial Endocarditis concluded that patients undergoing dental procedures must be protected by high concentrations of antibiotic present in the blood at the time of the procedure. Penicillin administered parenterally was preferred, although oral penicillin V was introduced as second choice. In cases of sensitivity to penicillin, other antibiotics such erythromycin or tetracycline were recommended [2].

Since that time, the scientific community has universally accepted the need for antibiotic prophylaxis in patients susceptible to developing IE. Experimental models developed in the 1970s provided evidence of the efficacy of prophylaxis in animals and demonstrated the ability of antibiotics to prevent *Streptococcus sanguinis* endocarditis [3]. However, the different antibiotic regimens to prevent IE in dental patients were developed based on empirical criteria.

In 1982, the British Society for Antimicrobial Chemotherapy included amoxicillin in the prophylactic antibiotic regimen against IE [4]. Amoxicillin has a broad antibacterial spectrum and a more favourable pharmacokinetic profile than penicillin V for oral administration; this has made it the drug of choice in all current guidelines on the use of antibiotics to prevent IE.

The main inclusion criteria for the prophylactic regimens established by the first committees were the rheumatic heart disease and congenital malformations, but fundamental changes have been introduced since that time regarding "patients considered to be at risk of IE". The campaigns for the prevention of rheumatic fever, the increase in the prevalence of intravenous drug abuse and the growth in cardiovascular interventions have transformed the microbiological patterns of IE, with a relative decrease in the incidence of streptococcal endocarditis and a significant increase in endocarditis due to staphylococci and other less common organisms.

These changes make it difficult to draw reliable epidemiological conclusions on the efficacy of antibiotics for the prevention of IE. In general, the majority of studies indicate that, despite the universal implantation of antibiotic prophylaxis prior to the dental treatment, no global reduction in the prevalence of IE has been achieved [5].

This has been one of the main arguments put forward by the British health authorities to revoke the indications for antibiotic prophylaxis in patients undergoing dental, digestive tract or genitourinary interventions. A few years ago, the National Institute for Health and Clinical Excellence (NICE) in the United Kingdom published a proposal that surprised the scientific community by considering that "antibiotic prophylaxis for IE was not recommended for persons undergoing dental treatment". This recommendation was even applicable to "highrisk patients, independently of the type of dental procedure they were to undergo" [6].

This scepticism of the British health authorities to the prophylactic efficacy of antibiotics in IE is not shared by other scientific societies, which continue to include antibiotic cover for dental procedures in patients at risk of developing IE.

Epidemiological observations and statistical analyses made after the cessation of prophylaxis in the United Kingdom suggest the need for antibiotic cover in patients at maximum risk of IE of poor prognosis. In this setting, current guidelines maintain the need for prevention for patients considered to be at high risk of developing IE, such as individuals with prosthetic heart valves, the presence of certain congenital cardiopathies and patients who have had a previous episode of IE.
