CITATION: Pichichero ME. 1996. Ask the Expert. APUA Newsletter 14(1):7.


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Ask the Expert

Is penicillin still the antibiotic of choice for streptococcal pharyngitis?
Michael E Pichichero, MD
Departments of Microbiology and Immunology, Pediatrics and Medicine, University of Rochester Medical Center, Rochester, New York, USA


Patients who seek medical care for sore throat are usually concerned about the possibility of streptococcal tonsilllopharyngitis. However, fewer than 10% of adults and 30% of children actually have a streptococcal infection. Viruses and idiopathic causes account for the majority of sore throat complaints.

Reliance on clinical impression to diagnose streptococcal tonsillopharyngitis is problematic; an overestimation of 80 to 95% by experienced clinicians typically occurs for adult patients. Overtreatment promotes bacterial resistance, disturbs natural microbial ecology and may produce unnecessary side effects. Rapid streptococcal antigen testing as an aid to clinical diagnosis can be helpful when used appropriately. It is 80 to 90% sensitive in detecting group A beta-hemolytic streptococcus in throat swabs and 90 to 95% specific in eliminating streptococcal infection as a consideration in rapid test-negative patients. Detection of streptococci by rapid antigen tests or throat culture has consistently been shown to be a cost-effective strategy in the management of sore throat, independent of the issues surrounding antibiotic overuse.

Penicillin remains the gold standard of therapy for streptococcal tonsillopharyngitis. For those physicians who are unconvinced about the necessity for and value of rapid antigen streptococcal detection or throat cultures, selection of broader antimicrobials as empiric therapy cannot be advocated. Too often clinicians apply scientific research findings regarding the treatment of laboratory-confirmed streptococcal pharyngitis to all patients with sore throat. This application is a mistake as it results in substantial overuse of antibiotics.

Cephalosporins have now been demonstrated repeatedly to produce an enhanced bacteriologic and clinical cure for streptococcal tonsillopharyngitis, but their use can be assigned to special situations. Their empiric administration to all patients with sore throat would be a great concern, given the frequency with which antibiotics are prescribed for this condition.

A number of explanations have been suggested for bacteriologic failures after penicillin treatment of streptococcal pharyngitis: poor compliance, presence of copathogens producing a beta-lactamase (which inactivates penicillin in vivo) and the unintentional eradication of normally protective commensal bacteria that colonize the throat. Each of these issues will be briefly examined.

Compliance
Unfortunately, patients are often noncompliant with oral medications. Penicillin or amoxicillin are usually prescribed for three times daily administration for 10 days for streptococcal tonsillopharyngitis. This frequency of administration leads to reduced compliance. In a hospital-based pediatric clinic, 56% of children had stopped taking penicillin for streptococcal pharyngitis by the third day, 71% by the 6th day and 82% by the 9th day. Symptoms of acute streptococcal tonsillopharyngitis subside quite promptly with appropriate therapy such that patients feel completely well within two to three days of initiation of treatment. As a consequence of this improved feeling of well-being, motivation to continue oral therapy diminishes and compliance drops precipitously.

Copathogenicity
Penicillin therapy may fail in some patients because the antibiotic is rendered inactive as a consequence of co-colonization with copathogenic bacteria that elaborate beta-lactamases, such as Staphylococcus aureus, Hemophilus influenzae, H. parainfluenzae, Moraxella catarrhalis and a variety of anaerobes. Because prior penicillin treatment significantly increases the percentage of beta-lactamase-producing bacteria in the tonsillopharynx, penicillin may not be effective. In such cases, the copathogenic bacteria protect the pathogenic streptococci from the action of penicillin by degrading the penicillin and rendering it ineffective.

Microbial Ecology
A number of bacteria normally colonize the tonsillopharynx. These flora protect the throat and tonsils against infection by interfering with the ability of Streptococcus pyogenes to initiate and/or maintain colonization. These normal flora elaborate bacteriocins--natural antibiotic substances. Bacteriocins are produced by various species of alpha-hemolytic streptococci, and these protective bacteria are normally present in significant numbers in the tonsillopharynx. The natural microbial balance can be disturbed by the use of antibiotics. When patients receive penicillin or amoxicillin, levels that are bactericidal against normally protective alpha-hemolytic streptococci are readily achieved. This effect is achieved less with cephalosporins because of the relative resistance of alpha-hemolytic streptococci to eradication by this class of antibiotics.

Patients with laboratory-confirmed (rapid antigen detection or culture) streptococcal tonsillopharyngitis who are more likely to benefit from the use of cephalosporins or other broader-spectrum beta-lactamase-stable antibiotics are those

  • with a documented treatment failure with penicillin
  • with repeated streptococcal tonsillopharyngitis
  • recently treated with penicillin or amoxicillin for any prior indication
  • who are likely to be poorly compliant with antibiotic regimens requiring three times daily dosing for 10-day treatment courses

Otherwise, penicillin generally remains the antibiotic of choice for streptococcal pharyngitis.

 

ALLIANCE FOR THE PRUDENT USE OF ANTIBIOTICS © 1999

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