This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
A 65-year-old male from bihar with a pneumonia has a sputum culture that is positive for a staphylococcal strain that is b-lactamase- positive. Which is the best choice of penicillin therapy in this patient? 
Select and explain. 
A. Ampicillin, B. Oxacillin, C. Ticarcillin, D. Penicillin G
B: Oxacillin
Answer: B: Oxacillin 
Explanation: 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.