Dicloxacillin:- Anti - staphylococcal penicillin :- B lactamase resistant penicillin. Their use is restricted to the treatment of infection cause by penicillinase producing staphylococci including MSSA. Other drug of this class:- Methicillin Oxacillin Methicillin because of its toxicity (interstitial Nephritis), Methicillin is not used. Ampicillin/Amoxicillin:-Extended- Spectrum penicillin. More effective against gram -ve bacilli. Ampicillin is a drug of choice for gram positive bacilli : listeria monocytogenes Ceftazidime:-3rd gen cephalosporin, has activity against P. aeruginosa Ciprofloxacin: of the fluoroquinolone it has best activity against P. Aeruginosa and is commonly used in cystic fibrosis patient.