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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:
  1. https://www.drugs.com/pro/unasyn.html
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC187700/
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC163064/
  4. http://www.antimicrobe.org/b237tabrev.htm#tab2
  5. Clinical Practice Guidelines for the Diagnosis and Management of Intravascular Catheter-Related Infection: 2009 Update by the Infectious Diseases Society of America

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