Prophylaxis for infective endocarditis
Who needs it? How effective is it?
Natasha Press, MD, FRCPC Valentina Montessori, MD, FRCPC
OBJECTIVETo review guidelines for using antibiotic prophylaxis to prevent infective endocarditis, and to present recent changes and controversies regarding these guidelines.
QUALITY OF EVIDENCEData are from physiologic and in vitro studies, as well as studies of animal models, and from retrospective analyses of human endocarditis cases. Systematic reviews and guidelines are also examined. As no randomized clinical trials have examined prophylaxis for bacterial endocarditis, many recommendations presented are based on consensus guidelines.
MAIN MESSAGEAntibiotic prophylaxis to prevent bacterial endocarditis should be used in high- and moderate-risk patients with cardiac disease. It should be given before procedures in which bacteremias are likely with organisms that cause endocarditis, such as viridans streptococci. For most procedures, a single dose of amoxicillin (2 g by mouth 1 hour before the procedure) is sufficient to ensure adequate serum levels before and after the procedure.
CONCLUSION Infective endocarditis continues to have high rates of morbidity and mortality.
Antibiotic prophylaxis, therefore, is important to combat this preventable disease. For high- and moderate-risk patients with cardiac disease, the cost-benefit ratio favours prophylaxis.
OBJECTIFPasser en revue les lignes directrices concernant l’antibioprophylaxie pour prévenir l’endocardite infectieuse et présenter les modifications récentes aux directives ainsi que les controverses qui les entourent.
QUALITÉ DES DONNÉES Les données sont tirées d’études physiologiques et in vitro, d’études sur des animaux et d’analyses rétrospectives de cas d’endocardite chez l’humain. Les études systématiques et les directives font aussi l’objet d’une analyse. Étant donné l’absence d’essais cliniques aléatoires concernant la prophylaxie contre l’endocardite bactérienne, plusieurs des recommandations présentées se fondent sur des lignes directrices consensuelles.
PRINCIPAL MESSAGEL’antibioprophylaxie pour prévenir l’endocardite bactérienne devrait être utilisée chez les patients à risque modéré et élevé souffrant de cardiopathies. Elle devrait être administrée avant les interventions susceptibles de causer des bactériémies par des organismes à l’origine des endocardites, comme les streptocoques viridians. Dans la majorité des interventions, une seule dose d’amoxicilline (2 g par voie orale, une heure avant l’intervention) est suffisante pour assurer des taux sériques adéquats avant et après l’intervention.
CONCLUSION L’endocardite infectieuse continue de produire des taux élevés de morbidité et de mortalité. Il importe donc de recourir à l’antibioprophylaxie pour lutter contre cette maladie que l’on peut prévenir. Chez les patients à risque élevé et modéré souffrant de cardiopathies, le ratio coûts-avantages est favorable à la prophylaxie.
This article has been peer reviewed.
Cet article a fait l’objet d’un évaluation externe.
Can Fam Physician2000;2248-2255.
résumé abstract
espite advances in diagnosis and treat- ment, bacterial endocarditis continues to have a high mortality rate (approximately 37%).1The most frequent causes of death are congestive heart failure or neurologic and septic complications with embolic phenomena or rupture of mycotic aneurysms.1,2
In patients surviving endocarditis, such complica- tions as valvular dysfunction affect overall longevity.3,4 Prevention of bacterial endocarditis, therefore, is very important. In this era of increasing antibiotic resis- tance, prevention of endocarditis gains greater impor- tance because treatment for Gram-positive organisms is less effective than it once was.
Bacterial endocarditis is an infection of the endo- cardium characterized by formation of vegetation. A heart valve is usually involved but the infection can occasionally involve a septal defect or mural endo- cardium. Sterile vegetations sometimes form over areas of trauma to the endothelium, at the site of an intracardiac foreign body, or in areas of turbulence (as in valvular insufficiency). A sterile vegetation can then become infected when bacteremia is caused by an organism that adheres to platelets, fibrin, and fibronectin (eg, viridans streptococci). Bacteremia can occur secondary to localized infection, such as pneumonia, or to surgical or dental procedures dur- ing which using instruments on mucosal surfaces leads to transient bacteremias, usually lasting less than 15 minutes.5-21 Occasionally, more pathogenic organisms, such as Staphylococcus aureus, infect apparently normal valves.
No randomized or controlled human trials in patients with underlying structural hear t disease have explored the relationship between antibiotic prophylaxis and development of bacterial endo- carditis. The role of antibiotic prophylaxis in pro- tecting against infective endocarditis during bacteremia-inducing procedures has not been fully defined. In fact, many cases of bacterial endocardi- tis are not directly attributable to invasive proce- dures. Approximately 15% to 20% of cases of Streptococcus viridans endocarditis have a histor y of dental work, and up to 50% of patients with ente- rococcal endocarditis report recent gastrointestinal or genitourinar y procedures.22 For tunately, in developed countries, the overall rate of bacterial
endocarditis is low, estimated at 15 to 30 cases per million per year; 75% of these patients have pre- existing cardiac abnormalities.23
In general, the strategy of using prophylactic antibi- otics to prevent bacterial infection is most likely to be clinically effective and cost effective when a specific antibiotic is directed against a specific organism and when the disease occurs relatively frequently.24 In the case of bacterial endocarditis, efforts have been made to select antibiotic regimens aimed as narrowly as pos- sible at the most likely pathogens, and prophylaxis is considered reasonable in high- and moderate-risk patients. Thus, although risk of endocarditis in the gen- eral population is small, and no clinical trials are avail- able to prove efficacy, the high rates of endocarditis morbidity and mortality support antibiotic prophylaxis in patients with underlying cardiac lesions undergoing procedures known to be associated with bacteremia.
Recommendations for using antibiotic prophylaxis consider the host’s predisposition for developing bac- terial endocarditis, procedures that have a substantial risk of bacteremia, adverse effects of antibiotic pro- phylaxis, and a cost-benefit analysis. This article will address which patients require antibiotic prophylaxis and for which types of procedures. In addition, it will examine the effectiveness of antibiotic prophylaxis in preventing bacterial endocarditis. The 1997 guide- lines of the American Heart Association (AHA) will be discussed in light of recent studies.
Quality of evidence
A MEDLINE search was performed using the MeSH words endocarditis, bacterial, and the key word pro- phylaxis. No randomized controlled trials were avail- able. Data from smaller physiologic and in vitro studies were included, as were studies of animal models and retrospective analyses of human endo- carditis cases. Prospective clinical studies of the pro- phylactic ef ficacy of antibiotics are unavailable because an excessively large number of patients would be required to reach a significant conclusion.25 Because of the complexity of published data, repre- sentative findings from systematic reviews and guide- lines for treatment are summarized in this paper. Of particular importance are recommendations from the AHA, which has provided a statement on prevention of bacterial endocarditis based on available data as well as on expert opinion.26This statement was con- ceived to maintain a cost-effective prevention strategy while reducing factors that lead to overuse of antimi- crobial agents, excessive costs, and risk of adverse drug reactions.26
D
Dr Pressis an Infectious Diseases Fellow at the University of British Columbia in Vancouver.
Dr Montessoriis an Infectious Diseases Consultant at St Paul’s Hospital and the University of British Columbia.
Synthesis
Results of studies were reviewed with a focus on four areas: which patients? which procedures? which antibiotics? and how effective?
Which patients? Studies have shown that patients with certain types of structural cardiac disease are at higher risk of developing endocarditis.27 Fur ther, when endocarditis does develop in these patients, outcomes var y.26Prophylaxis, therefore, is recom- mended for patients with a higher risk of developing endocarditis and for whom higher morbidity is asso- ciated with the disease.
Patients at high risk include those with prosthetic heart valves, patients who have previously had endo- carditis, patients with complex cyanotic congenital heart disease, and patients with surgically construct- ed systemic-pulmonic shunts. Patients at moderate risk include patients with congenital or acquired valvular dysfunction, such as aortic stenosis or mitral regurgitation, and patients with hyper trophic car- diomyopathy. Patients with congestive heart failure associated with acquired valval dysfunction should receive prophylaxis, whereas patients with conges- tive heart failure but no valvular abnormalities do not require prophylaxis. The AHA guidelines stratify car- diac conditions into high- and moderate-risk cate- gories primarily on the basis of the risk that each poses for development of endocarditis (Table 1).
Controversy exists over antibiotic prophylaxis for patients with mitral valve prolapse, which is found in 4% of the adult population. It is often related to vol- ume status, adrenergic state, or growth phase, and is not an abnormality of valve structure or function.
If the valves are normal, but, nevertheless, prolapse and cause systolic clicks, the risk of endocarditis is not increased above that of the normal population.27-29 Patients with normal valves who have echocardio- graphic evidence of minimal leaks do not appear to be at increased risk for endocarditis.27-29If the valves are insuf ficient, however, causing a murmur or echocardiograph-demonstrated mitral regurgitation, then antibiotic prophylaxis is recommended. Mitral insufficiency associated with prolapsing valves cre- ates the shear forces and turbulent flow that increase the likelihood of vegetation formation and bacterial adherence on the valve during bacteremia.26 Patients with prolapsing and leaking mitral valves (evidenced by audible clicks and mur- murs of mitral regurgitation or by echocardiograph- demonstrated mitral regurgitation) should receive prophylactic antibiotics.29-33This policy is supported
Table 1.Cardiac conditions associated with endocarditis
ENDOCARDITIS PROPHYLAXIS RECOMMENDED
High risk
• Prosthetic cardiac valves, including bioprosthetic and homograft valves
• Previous bacterial endocarditis
• Complex cyanotic congenital heart disease (eg, single ventricle states, transposition of the great arteries, Fallot’s tetralogy)
• Surgically constructed systemic pulmonic shunts or conduits
Moderate risk
• Most other congenital cardiac malformations (other than those mentioned above and below)
• Acquired valvar dysfunction (eg, rheumatic heart disease)
• Hypertrophic cardiomyopathy
• Mitral valve prolapse with valvar regurgitation or thickened leaflets
ENDOCARDITIS PROPHYLAXIS NOT RECOMMENDED
Negligible risk (no greater risk than general population)
• Isolated secundum atrial septal defect
• Surgical repair of atrial septal defect, ventricular septal defect, or patent ductus arteriosus (without residua beyond 6 mo)
• Previous coronary artery bypass graft surgery
• Mitral valve prolapse without valvar regurgitation
• Physiologic, functional, or innocent heart murmur
• Previous rheumatic fever without valvar dysfunction
• Previous Kawasaki disease without valvar dysfunction
• Cardiac pacemakers (intravascular and epicardial) and implanted defibrillators
Reprinted with permission from Dajani et al (Journal of the American Medical Association 1997;277:1794-801. Copyright 1997, American Medical Association).26
by formal cost-benefit analysis.34Table 2 summa- rizes current recommendations on prophylaxis for patients with mitral valve prolapse.
Patients with myxomatous degeneration of the mitral valve could also have mitral valve prolapse. In some patients, prolapse is evident only with changes in heart rate or volume status. Patients with myxoma- tous degeneration with regurgitation are candidates for antibiotic prophylaxis. Some patients with myxo- matous degeneration do not have a murmur at rest but develop it with exercise. Patients with exercise- induced mitral regurgitation were not shown, in one small series, to be at increased risk for endocarditis.35 However, other studies have shown that men older than 45 years are at increased risk for endocardi- tis.34,36Therefore, men older than 45 years with mitral valve prolapse but without a consistent murmur should be offered prophylaxis even in the absence of resting regurgitation.
Which procedures? It is important to realize that transient bacteremias are common. They occur not only during procedures, but also during ever yday activities, such as br ushing teeth and chewing.
Although these ever yday activities can cause fre- quent transient bacteremias, it would be impractical to attempt to prevent them. During health care proce- dures, frequency of bacteremias varies, and prophy- laxis is offered for procedures causing the greatest frequency of bacteremia.5,20 Antibiotic prophylaxis is recommended for procedures that are not only known to cause bacteremias, but, more importantly, are known to cause bacteremia with organisms com- monly associated with endocarditis (Table 3).
If a series of dental procedures is required, experts recommend waiting 9 to 14 days between each procedure. The delay allows repopulation of the mouth with normal flora and, therefore, reduces potential for organisms to gain resistance from fre- quent antibiotic use.37,38
Although colonoscopy has a rate of bacteremia ranging from 2% to 5%, organisms typically identified are unlikely to cause endocarditis.15,39Therefore antibiotic prophylaxis is not recommended for colonoscopy. This includes endoscopy with mucosal biopsy, polypectomy, or sphincterotomy.16,19,40
Which antibiotics? For dental, oral, respirator y tract, or esophageal procedures, S viridans (α-hemolytic streptococci) is the most common cause of endocarditis. The recommended prophy- laxis is amoxicillin (2 g administered 1 hour before
the anticipated procedure). This represents a change from previous recommendations, which included a dose after the procedure. Recent studies have shown that a second dose is unnecessar y because amoxicillin produces a prolonged (6 to 14 hours) increase in serum level above the minimal inhibitor y concentration of most oral streptococ- ci.41,42For patients unable to take oral medications, intravenous ampicillin (2 g within 30 minutes before the procedure) can be substituted. Patients allergic to penicillins can be given clindamycin (600 mg by mouth or intravenously). Previous recommenda- tions suggested use of er ythromycin, which was associated with poor gastrointestinal tolerance and with unreliable pharmacokinetics, which are depen- dent on which of various formulations is used.43 Other macrolides, such as clarithromycin (500 mg by mouth) or azithromycin (500 mg by mouth), or cephalosporins, such as cephalexin (2.0 g by mouth) or cefazolin (1.0 g intravenously), can also be used for penicillin-allergic patients.44Patients with imme- diate hypersensitivity reactions to penicillins should not receive cephalosporins.
For nonesophageal gastrointestinal procedures and for genitourinary procedures, Streptococcus fae- calis is most often responsible for causing endo- carditis. Recommended antibiotic prophylaxis for these procedures is described in Table 4. Although Gram-negative bacteremias occur following these procedures, they rarely cause endocarditis. For high-risk patients, intravenous antibiotics should be used. As well, physicians might want to offer pro- phylaxis to their high-risk patients undergoing pro- cedures for which antibiotic prophylaxis is not usually recommended.26
CLINICAL EXAMINATION ECHOCARDIOGRAM RESULT PROPHYLAXIS?
No murmur Normal No
No murmur Prolapsed valve, NO regurgitation
No
No murmur Prolapsed valve WITH regurgitation
Yes
Male > 45 years old, no murmur at rest
Prolapsed valve, NO regurgitation at rest
Yes
Regurgitant murmur
No echocardiogram necessary
Yes
Table 2.Endocarditis prophylaxis for patients with mitral valve prolapse
Table 3.Endocarditis prophylaxis with various procedures
DENTAL PROCEDURES: ENDOCARDITIS PROPHYLAXIS RECOMMENDED Dental extractions
Periodontal procedures including surgery, scaling and root planing, probing, and recall maintenance
Dental implant placement and replantation of avulsed teeth Endodontic (root canal) instrumentation or surgery only beyond the apex
Subgingival placement of antibiotic fibres or strips Initial placement of orthodontic bands but not brackets Intraligamentous local anesthetic injections
Prophylactic cleaning of teeth or implants where bleeding is anticipated
DENTAL PROCEDURES: ENDOCARDITIS PROPHYLAXIS NOT RECOMMENDED
Restorative dentistry (operative and prosthodontic) with or without retraction cord
Local anesthetic injections (nonintraligamentous)
Intracanal endodontic treatment; post placement and buildup Placement of rubber dams
Postoperative suture removal
Placement of removable prosthodontic or orthodontic appliances
Taking of oral impressions Fluoride treatments Taking of oral radiographs Orthodontic appliance adjustment Shedding of primary teeth
OTHER PROCEDURES: ENDOCARDITIS PROPHYLAXIS RECOMMENDED Respiratory tract
• Tonsillectomy or adenoidectomy
• Surgical operations that involve respiratory mucosa
• Bronchoscopy with a rigid bronchoscope
Gastrointestinal tract
• Sclerotherapy for esophageal varices
• Esophageal stricture dilation
• Endoscopic retrograde cholangiography with biliary obstruction
• Biliary tract surgery
• Surgical operations that involve intestinal mucosa Genitourinary tract
• Prostatic surgery
• Cystoscopy
• Urethral dilation
OTHER PROCEDURES: ENDOCARDITIS PROPHYLAXIS NOT RECOMMENDED Respiratory tract
• Endotracheal intubation
• Bronchoscopy with a flexible bronchoscope, with or without biopsy (prophylaxis optional for high-risk patients)
• Tympanostomy tube insertion Gastrointestinal tract
• Transesophageal echocardiography (prophylaxis optional for high-risk patients)
• Endoscopy with or without gastrointestinal biopsy (prophylaxis optional for high-risk patients) Genitourinary tract
• Vaginal hysterectomy (prophylaxis optional for high-risk patients)
• Vaginal delivery (prophylaxis optional for high-risk patients)
• Cesarean section
• In uninfected tissue:
Urethral catheterization Uterine dilation and curettage Therapeutic abortion
Sterilization procedures
Insertion or removal of intrauterine device Other
• Cardiac catheterization, including balloon angioplasty
• Implanted cardiac pacemakers, implanted defibrillators, and coronary stents
• Incision or biopsy of surgically scrubbed skin
• Circumcision From Dajani et al.26
Special situations.Patients taking antibiotics to pre- vent recurrence of acute rheumatic fever should still receive the recommended antibiotic prophylaxis to prevent infective endocarditis. Prophylactic doses for rheumatic fever are too low to prevent infective endo- carditis. As well, a different class of antibiotic should be used, as patients could have developed organisms resistant to their current antibiotics. For example, patients taking oral penicillin for secondary preven- tion of rheumatic fever could have viridans streptococ- ci in their oral cavities that are relatively resistant to penicillin, amoxicillin, or ampicillin. Therefore, they should be given clindamycin, clarithromycin, or azithromycin for endocarditis prophylaxis.
If a procedure involves incision or drainage of infected tissue, it is advisable to administer antimicro- bial prophylaxis before the procedure. Prophylaxis should be directed at the known pathogen or the most likely pathogen. For example, if a joint is infect- ed with methicillin-resistant S aureus, vancomycin is the drug of choice. For dermatologic surgery on non- infected, surgically scrubbed skin, no prophylaxis is necessary.26
Although most studies are of adults, studies of children have shown that bacteremia occurs in a sub- stantial proportion after dental procedures. Children at risk, therefore, should receive antibiotic prophylax- is for infective endocarditis, with appropriate adjust- ment of doses.45
Pregnant women should be treated as necessary.
Between 1% and 5% of vaginal deliveries are associat- ed with bacteremia, usually with streptococci.46High- risk patients (Table 1) could be offered prophylaxis.
Amoxicillin, as previously described, would be the agent of choice. No prophylaxis is required for cesarean sections or routine therapeutic abortions.26
How effective?Most cases of bacterial endocarditis are not preceded by a procedure. In cases that are procedure-related, endocarditis occurs within a short incubation period of approximately 2 weeks after the procedure.47From 1979 to 1982, an AHA committee collected and recorded examples of apparent preven- tion failures. Among 52 such cases, 92% followed a dental procedure and 75% were caused by viridans streptococci. Most patients received oral penicillin for prophylaxis, and 60% of organisms for which antimi- crobial susceptibility was known were sensitive to the antibiotics used for prophylaxis. This study demon- strated that endocarditis prophylaxis failures are not rare and that failures occur even when the infecting organism is susceptible to the antibiotics used.48
A recent large-scale, population-based case-control study, done in 54 Philadelphia, Pa, area hospitals from 1988 to 1990, was unable to demonstrate any independent risk for endocarditis attributable to den- tal treatment. In this study, no particular type of den- tal work was significantly linked to infective endocarditis, not even tooth extraction. The authors, while acknowledging that dental procedures can cause endocarditis, argue that this happens too rarely to justify routine use of antibiotic prophylaxis.49
Based on these conclusions, some experts believe that prophylaxis should be downgraded to “not rec- ommended” for most dental procedures, but still maintained for potentially high-risk procedures, such as extractions and gingival surger y (including implant placement), and downgraded to “not recom- mended” for most underlying cardiac conditions
RISK ASSESSMENT AGENTS REGIMEN
High-risk patient Ampicillin plus gentamicin
Ampicillin 2.0 g IM or IV plus gentam- icin 1.5 mg/kg (not to exceed 120 mg) within 30 min of starting procedure;
6 h later, ampicillin 1 g IM or IV or amoxicillin 1 g orally High-risk patients
allergic to penicillin
Vancomycin plus gentamicin
Vancomycin 1.0 g IV over 1-2 h plus gen- tamicin 1.5 mg/kg (not to exceed 120 mg); complete injection or infusion within 30 min of starting procedure Moderate-risk
patients
Amoxicillin or ampicillin
Amoxicillin 2.0 g orally 1 h before procedure, or ampicillin 2.0 g IM or IV within 30 min of starting procedure Moderate-risk
patients allergic to penicillin
Vancomycin Vancomycin 1.0 g IV over 1-2 h; complete infusion within 30 min of starting procedure From Dajani et al.26
Table 4.Prophylactic regimens for
genitourinar y and gastrointestinal (excluding esophageal) procedures
except prosthetic valves and previous endocarditis.
Benefits for reduced use of antibiotic prophylaxis include fewer side effects, lower costs for third-party payers, and less selection for antibiotic resistance.50 Until other studies are published to validate this study, continuing to follow recommended guidelines for dental procedures is warranted because morbidity and mortality associated with developing endocardi- tis is so high.
Discussion
Unfortunately, the evidence for antibiotic prophylaxis is not strong. It would, however, be extremely diffi- cult to design a randomized controlled trial because of the low frequency of endocarditis as a complication following bacteremia-inducing procedures and because of the high morbidity and mortality associat- ed with the disease. Future research will likely con- sist of retrospective and prospective case-control studies. Areas that require fur ther exploration include mitral valve prolapse, dental procedures, and low-risk procedures in high-risk patients.
Conclusion
Antibiotic prophylaxis to prevent bacterial endocardi- tis should be used in high- and moderate-risk patients with cardiac disease. It should be given before proce- dures in which bacteremias are likely with organisms that cause endocarditis, such as viridans streptococci.
For most procedures, a single dose of antibiotics 1 hour before the procedure is sufficient to ensure adequate serum levels before and after the procedure.
Although one recent study was unable to demonstrate a link between dental work and endocarditis, AHA guidelines should be followed until further studies val- idate this result. For high- and moderate-risk patients, the cost-benefit ratio favours prophylaxis.
Correspondence to: Dr V. Montessori, 667—1081 Burrard St, Vancouver, BC V6Z 1Y6; telephone (604) 806-8644; fax (604) 806-8527; e-mail valm@hivnet.ubc.ca
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Key points
• Antibiotic prophylaxis is recommended to prevent bacterial endocarditis only in high- and moderate- risk patients with heart disease.
• This update is based on information from case-con- trol and descriptive studies, not randomized con- trolled trials, and on cost-benefit analysis of the severity of morbidity and mor tality when endo- carditis is established.
• For most procedures, a single dose of antibiotics (usually 2 g of amoxicillin) 1 hour before the proce- dure is adequate.
• Mitral prolapse without a murmur and echocardio- graphic evidence of regurgitation does not normal- ly require prophylaxis; men older than 45 with this condition could require prophylaxis.
Points de repère
• L’antibioprophylaxie est recommandée pour prévenir les endocardites bactériennes chez les patients à risque élevé et modéré souffrant de car- diopathies.
• Cette mise à jour se fonde sur l’information tirée d’études de cas-témoins et descriptives, mais pas sur des essais aléatoires contrôlés. Elle comporte aussi une analyse des coûts-avantages en fonction de la sévérité de la morbidité et de la mortalité une fois que l’endocardite est établie.
• Dans la plupart des inter ventions, il suffit d’une seule dose d’antibiotique (habituellement 2 g d’amoxicilline) une heure avant.
• Le prolapsus valvulaire mitral sans souffle ni évi- dence échocardiographique de régurgitation ne nécessite habituellement pas de prophylaxie; les hommes de plus de 45 ans pourraient en avoir besoin.
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