Flucloxacillin’s primary target is Gram-positive bacteria. It effectively treats infections caused by Staphylococcus aureus (including methicillin-sensitive S. aureus or MSSA), Streptococcus pyogenes (Group A Streptococcus), and Streptococcus pneumoniae. However, resistance is a growing concern.
Resistance to flucloxacillin, particularly among S. aureus strains, is largely due to the production of beta-lactamases. Methicillin-resistant S. aureus (MRSA) is inherently resistant.
| Staphylococcus aureus (MSSA) | High | Beta-lactamase-negative strains are susceptible. |
| Staphylococcus aureus (MRSA) | Resistant | Inherent resistance due to altered penicillin-binding proteins. |
| Streptococcus pyogenes | High | Generally susceptible, but susceptibility testing is recommended. |
| Streptococcus pneumoniae | Variable | Susceptibility varies geographically and over time. Testing is crucial. |
| Gram-negative bacteria | Low or None | Flucloxacillin is generally inactive against Gram-negative organisms. |
Regular susceptibility testing is paramount to guide appropriate antibiotic selection. Local antibiograms provide valuable data on prevailing resistance patterns within a specific region. Always consider the results when prescribing flucloxacillin.
