 PENICILLINS  CEPHALOSPORINS  MONOBACTAMS  CARBAPENEMS  ORIGINALLY OBTAINED FROM FUNGUS PENICILLIUM NOTATUM.  DISCOVERED IN 1928.  AL. FLEMMING WAS WORKING IN HIS LAB TRYING TO KILL A DEADLY BACTERIA WHEN HE NOTICED A BLUE MOULD GROWING ON THE DISH (NOTATUM), AROUND THAT BACTERIA WERE GETTING KILLED.  PENICILLIN FOUND IN THIS MOULD  NOW FROM P.CHRYSOGENUM BECAUSE AMOUNT GOT FROM NOTATUM NOT SUFFICIENT. The mould Penicillum notatum amidase A B A THIAZOLIDINE RING ( A ) ATTACHED TO β –LACTAM RING ( B) THAT CARRIES A SECONDARY AMINO GROUP  β LACTAM RING CARRIES A SECONDARY AMINO GROUP TO WHICH SIDE CHAINS ATTACHED THROUGH AN AMIDE LINKAGE.  PEN.G ( PROTOTYPE) – BENZYL SIDE CHAIN.  SIDE CHAINS SPLIT OFF BY AN AMIDASE TO PRODUCE –  6-AMINOPENCILLANIC ACID.  A narrow spectrum antibiotic  Mainly against gram positive bacteria  Streptococci  Pneumococci  B.Anthracis  Corynebacterium diphtheriae  Clostridia  Listeria  Treponema pallidum  Actinomyces israelii  Gram negative cocci - N.gonorroeae and meningitidis  Pen.G is acid labile. Give 30 min before or 2 hrs after meals.  Very rapid renal excretion  10% by glomerular filteration  Rest by tubular secretion (ts)  Ts can be blocked by probenecid  To get higher and longer lasting plasma conc.  Insoluble salts of pen.G.  Repository prep : release pen.G slowly.  Given deep i/m.  Procaine pen. 0.5 – 1mu,12-24 hrly as aq. suspension.  Plasma conc. Sustained for 1-2 days.  BENZATHINE PEN. –  Extremely slow release of pen.  0.6-2.4 mu every 2- 4 wks.  Effective for prophylactic purposes for upto 4 wks.