strep and penicillin resistance

Ingvar.Eliasson at alinks.se Ingvar.Eliasson at alinks.se
Wed Jan 4 17:50:12 EST 1995


> My son has had two strep infections in the last three weeks.  
> The doctor keeps prescribing amoxicillin for it claiming that 
> S. pyogenes isn't able to develop resistance to this 
> antibiotic. Does anyone know if this is true and if so why?

There are still no clinical strains of S.pyogenes (=Group A 
Streptococci - GAS) that are penicillin resistant. However, 
claiming that this bug is not capable of developing resistance 
towards penicillin is probably overoptimistic. 

Phenoxymethyl-penicillin is a good first-choice drug for the 
treatment of primary acute tonsillitis. Amoxicillin should be 
equally effective, but has an unnecessarily broad spectrum of 
activity, and can thus be expected to cause a higher degree of 
selection of betalactam-resistant strains in the throat and 
gastrointestinal tract. In fact, several independent studies has 
demonstrated a dramatic increase in the recovery of betalactamase 
producing strains after a single episode of betalactam treatment, 
an effect that persists over several months.

Due to several factors, including the possible selection of 
betalactamase producing commencals like S.aureus, Haemophilus and 
Moraxella species, and anaerobes in the respiratory tract flora, 
phenoxymethyl-penicillin and amoxicillin are probably less 
recommendable in the treatment of recurrent tonsillitis (though 
these drugs work well in a majority of cases). If you experience 
therapeutic failure or rapid relapse, several second-line drugs 
are available. Personally, I prefer clindamycin or cefadroxil (or 
any of the new generation of betalactamase-stable peroral 
cephalosporins). One might argue that erythromycin would be a 
logical choice, but experience has shown that it is important to 
keep the prescriptions of macrolides to a minimum in order to 
avoid rapid resistance development. In Sweden, the frequency of 
resistance towards macrolides among clinical isolates of 
S.pyogenes vary regionally between 2 and 11%. Clindamycin 
resistance is below 1%. The resistance towards doxycyklin 
(another overprescribed drug) among clinical isolates of 
S.pyogenes is similar to that of erythromycin.

Finally, don't forget the epidemiological aspects when dealing 
with recurrent streptococcal infection? Is there a carrier in the 
family? How about spread at the day-care center?

When did you last give your local clinical microbiologist a 
throat swab?

Best regards

Ingvar

*****************************************
* Dr. Ingvar Eliasson, M.D., Ph.D.      *
* Dept. Clinical Microbiology           *
* County Hospital                       *
* S-391 85  Kalmar, Sweden              *
*                                       *
* Phone:..... +46-480-448772            *
* Fax:....... +46-480-81738             *
* Internet:.. Ingvar.Eliasson at alinks.se *
*****************************************




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