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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.
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