ASK DIS: Combination Antibiotic : Unasyn + Cloxacillin

Cloxacillin

Exhibits good activity against Staphylococcus aureus
has activity against many streptococci but is less active than penicillin and is generally not used in clinical practice to treat streptococcal infections

Unasyn

Ampicillin has a broad spectrum of bactericidal activity against many gram-positive and gram-negative aerobic and anaerobic bacteria

Comparison : Staphylococcus Aureus Coverage

Unasyn covers for both S. aureus (beta-lactamase and non-beta-lactamase producing)
Staphylococcal beta-lactamase is readily inhibited by the currently available beta-lactamase inhibitors clavulanic acid, sulbactam, and tazobactam. Thus, combination of these inhibitors with beta-lactamase-labile penicillins restores activity against penicillin-resistant, methicillin-susceptible staphylococci
Staphylococci resistant to methicillin, oxacillin, or nafcillin must be considered resistant to Unasyn.
When additional strains were used in the model, oxacillin and ampicillin-sulbactam (1,000 plus 2,000 mg/kg/day) were equally effective against both oxacillin-susceptible and borderline oxacillin-resistant strains of S. aureus
for strains in which the mechanism of resistance to S aureus is beta-lactamase production, piperacillin/tazobactam retains activity. There is no need to add a semisynthetic penicillin such as oxacillin

Rationale: Indications

Most causes of cellulitis are caused by streptococci and S. aureus, so that beta-lactam antibiotics with activity against penicillinase-producing S. aureus are the typical antibiotics of choice for uncomplicated cellulitis in an immunocompetent host
Ampicillin-sulbactam was highly effective in the prevention of experimental endocarditis caused by a beta-lactamase-producing, oxacillin-resistant coagulase-negative staphylococcal strain

Recommendations:

based on current guidelines, there is no rationale nor indication for combination of Unasyn and Cloxacillin
based on antibiotic spectrum and MIC, Unasyn will be able to cover for any other underlying S.Aureus infectionn

References:

ASK DIS