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A 65-year-old male with a pneumonia has a sputum culture that is positive for a staphylococcal strain that is β-lactamase-positive. Which is the best choice of penicillin therapy in this patient?

  1. Ampicillin

  2. Oxacillin

  3. Ticarcillin

  4. Penicillin G

  5. Carbenicillin


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The answer is b.
Oxacillin is classified as a penicillinase-resistant penicillin that is relatively acid-stable and, therefore, is useful for oral administration. Major adverse reactions include penicillin hypersensitivity and interstitial nephritis. With the exception of methicillin, which is 35% bound to serum proteins, all penicillinase-resistant penicillins are highly bound to plasma proteins. Oxacillin has a very narrow spectrum and is used primarily as an antistaphylococcal agent.