Flucloxacillin is highly effective against Streptococcus pyogenes (group A strep) and related species

A common myth – “Flucloxacillin and penicillin in combination are required to treat cellulitis”

NOT TRUE: monotherapy is adequate.

The two most common causative organisms in cellulitis (in order) are Streptococcus pyogenes) and Staphylococcus aureus. The mean Minimal Inhibitory Concentrations (MIC) of flucloxacillin for methicillin-susceptible S. aureus (MSSA) is 0.4 μg/ml and 0.04 for S. pyogenes (i.e. S. pyogenes is more sensitive than S. aureus to flucoxacillin).

Serum levels of dicloxacillin or flucoxacillin after usual doses are more than adequate for treatment.

And so, flucloxacillin alone is more than adequate to cover both S. aureus  and S. pyogenes infection.

Note that the widespread emergence of community strains of MRSA that cause skin and soft tissue infection – especially boils or cellulitis in association with venous ulcers may render di/flucloxacillin ineffective.



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    1. Hi Gabrielle

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  2. […] Infections due to these species of streptococci are usually rapidly responsive to appropriate antibiotic therapy which can be of short duration with no minimum IV requirement as endocarditis is not a usual consideration.  Penicillin resistance has not been documented and flucloxacillin is just as active (see this discussion). […]


  3. […] FLUCLOXACILLIN IS HIGHLY EFFECTIVE AGAINST STREPTOCOCCUS PYOGENES (GROUP A STREP) AND RELATED SPECI… (Jan 2015) – we returned to this topic to unpack a few more misconceptions this year in July with: […]


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