Antibiotic Prohylaxis : Does it Work

Over the past year there has been a flood of information disputing the effectiveness of antibiotic prophylaxis. Ever since the American Heart revised it's prophylactic regimen in 2007, every dental association has been quick to critisize the concept of prophylaxis. Ironically the criticism has been as vehment as the endorsements a few years back.

How much have things really changed? What do the findings mean for us clinically? IS prophylaxis no longer needed? DCSN looks at the long history of antibiotic prophylaxis regimen and the implications of the current regimen for special care dentistry.

• History
  
• Rationale
  
• Changes made and the reasons for those changes
• Clinical Implications
  

History of the anitbiotic prophylaxis regimen

The history of antibiotic prophylaxis is one of substantial ignorance and profound abuse.Although the rationale for infective endocarditis prophylaxis has been understood since the 1950's the application of this theory into practice has undergone many changes. The AHA has made recommendations for the prevention of IE for more than 50 years. 

from Wilson W et.al Prevention of infective endocarditis: Guidelines from the American Heart Association: A guideline from the American Heart Association Rheumatic Fever, Endocarditis and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group

J Am Dent Assoc 2007 138: 739-760

Between 1955 and 1997 the AHA guidelines were modified 8 times, each modification making allowance for previously unexplained phenomenon such as penicillin resistance, or the shift to safer drugs such as erythromycin and later clindamycin from more dangerous drugs such as chloramphenicol for penicillin allergic patients.The 1997 document stratified cardiac conditions into high-, moderate- and low-risk (negligible risk) categories with prophylaxis not recommended for the low-risk group. An even more detailed list of dental, respiratory, GI and GU tract procedures for which prophylaxis was and was not recommended was provided. The 1997 document was notable for its acknowledgment that most cases of IE are not attributable to an invasive procedure but rather are the result of randomly occurring bacteremias from routine daily activities and for acknowledging possible IE prophylaxis failures.

However despite this knowledge,it would take another 10 years before the AHA would put this knowledge into practice. The 2007 guidelines and their acceptance by the ADA in 2008, place a great emphasis on the role of transient bacteremia due to daily activities and greatly reduce the number of conditions where prophylaxis is required. This however DOES NOT mean that prophylaxis is not necessary or that the concept is redundant.

Rationale of antibiotic prophylaxis in dentistry

The development of IE is the net result of the complex interaction between the bloodstream pathogen with matrix molecules and platelets at sites of endocardial cell damage. In addition, many of the clinical manifestations of IE emanate from the host’s immune response to the infecting microorganism. The following sequence of events is thought to result in IE: formation of nonbacterial thrombotic endocarditis (NBTE) on the surface of a cardiac valve or elsewhere that endothelial damage occurs, bacteremia, adherence of the bacteria in the bloodstream to NBTE and proliferation of bacteria within a vegetation.

Formation of NBTE. Turbulent blood flow produced by certain types of congenital or acquired heart disease, such as flow from a high-to a low-pressure chamber or across a narrowed orifice, traumatizes the endothelium. This creates a predisposition for deposition of platelets and fibrin on the surface of the endothelium, which results in NBTE. Invasion of the bloodstream with a microbial species that has the pathogenic potential to colonize this site can then result in IE.

The conventional arguement has therefore been that any dental procedure would result in a transient bacteremia that would then trigger the formation of a vegetative thrombus in an individual who had a succeptible endothelium. Thus all invasive dental procedures carried out in succeptible individuals would require a prophylactic antibiotic regimen to avoid transient bacteremia.

The case against Prohylaxis

The primary case against prophylaxis has been one of effectiveness. It has been pointed out that no antibiotic can guarentee complete freedom from bacteremia and furthermore the chances of bacteremia from daily activities is far greater than many dental procedures

from Pallasch et al 2005 

The findings shown above greatly questioned the traditional view of the AHA, in 1997 the AHA for the first time admitted that the chances of bacteremia from daily oral hygiene procedures was as high as that of certain dental procedures. Keeping this in mind the AHA in 2007 revised their prophylactic regimen for dental procedures.

This however does not mean that prophylaxis is not required. It only reduced the individuals who required prophylaxis and eliminated a few procedures for which prophylaxis was required.

The reasons for change and changes made

The reasons for change and changes made

Based on the growing evidence of the ineffectiveness or lack of necessity of prophylaxis the american heart association in 2007 listed the only conditions which warrant the use of antibiotic prophylaxis it must be remembered howeveer that the findings in no way state the absence of the risk of endocarditis or alter the medication or doses in anyway. 

The findings also list the dental procedures for which the medication is required.

Specific situations and conditions

Patients already receiving antibiotics. If a patient is already receiving chronic antibiotic therapy with an antibiotic that is also recommended for IE prophylaxis for a dental procedure, it is prudent to select an antibiotic from a different class rather than to increase the dosage of the current antibiotic. For example, antibiotic regimens used to prevent the recurrence of acute rheumatic fever are administered in dosages lower than those recommended for the prevention of IE. Patients who take an oral penicillin for secondary prevention of rheumatic fever or for other purposes are likely to have viridans group streptococci in their oral cavity that are relatively resistant to penicillin or amoxicillin. In such cases, the provider should select either clindamycin, azithromycin or clarithromycin for IE prophylaxis for a dental procedure, but only for patients shown in Box 3. Because of possible cross-resistance of viridans group streptococci with cephalosporins, this class of antibiotics should be avoided. If possible, it would be preferable to delay a dental procedure until at least 10 days after completion of the antibiotic therapy. This may allow time for the usual oral flora to be re-established.

Patients receiving parenteral antibiotic therapy for IE may require dental procedures during antimicrobial therapy, particularly if subsequent cardiac valve replacement surgery is anticipated. In these cases, the parenteral antibiotic therapy for IE should be continued and the timing of the dosage adjusted to be administered 30 to 60 minutes before the dental procedure. This parenteral antimicrobial therapy is administered in such high doses that the high concentration would overcome any possible low-level resistance developed among mouth flora (unlike the concentrationthat would occur after oral administration).

Patients who receive anticoagulants. Intramuscular injections for IE prophylaxis should be avoided in patients who are receiving anticoagulant therapy (Class I, LOE A). In these circumstances, orally administered regimens should be given whenever possible. Intravenously administered antibiotics should be used for patients who are unable to tolerate or absorb oral medications.

Patients who undergo cardiac surgery. A careful dental evaluation is recommended so that required dental treatment may be completed whenever possible before cardiac valve surgery or replacement or repair of CHD. Such measures may decrease the incidence of late PVE caused by viridans group streptococci.

Taken from Wilson et al Prevention of infective endocarditis: Guidelines from the American Heart Association. JADA 2008 s 3-32 Full text available free