Flucloxacillin (INN) or floxacillin (USAN) is a narrow-spectrum beta-lactam antibiotic of the penicillin class. It is used to treat infections caused by susceptible Gram-positive bacteria.Unlike other penicillins, flucloxacillin has activity against beta-lactamase-producing organisms such as Staphylococcus aureus as it is beta-lactamase stable.However, it is ineffective against methicillin-resistant Staphylococcus aureus (MRSA).It is very similar to dicloxacillin; they are considered interchangeable.t is used to treat infections caused by susceptible Gram-positive bacteria. Unlike other penicillins, flucloxacillin has activity against beta-lactamase-producing organisms such as Staphylococcus aureus as it is beta-lactamase stable.