1. Penicillinase Resistant Penicillins ( PRP ) -1940, 90% S. aureus strains were sensitive to pen G -1960, 50% S. aureus were seusitive to pen G - -Beecham : synthesized thousands of semisynthetic Penicillins, Screened against P.P. S. aureus - Due to the bulky side chain in methicillin, it will not fit into the tube “ acive site ” -Methicillin is mainly excreted renally, Interstitial nephritis

2. Penicillinase Resistant Penicillins ( PRP ) Isoxazole PRP Oxacillin:- -Relatively orally active -Excreted both renally and hepatically -Oral absorption is incomplete due to high polarity - Cloxacillin is more lipophilic than oxacillin and has a better oral absorption - Dicloxacillin is the best in case of oral absorption - Dicloxacillin and flucloxacillin are used for mixed Staph & Strept infections

3. Penicillinase Resistant Penicillins ( PRP ) a- Tonsilitis, Dicloxacillin and better yet “ augmentin ® ” b- Impetigo “ Skin disease ” Dicloxacillin and better yet oral cefuroxime “ axetil ® ” and topical mupirocin “ Bactroban ® ” -The advantage of nafcillin is that it is excreted hepatically and is good candidate in case of renal insufficiency