Isopropyl Alcohol (Isopropanol) ACTION  AND  USE.—  This is used in a 70 percent solution as a skin antiseptic; it is volatile and also has a desiccating (drying) effect on the skin. Hexachlorophene   (pHisoHex) ACTION AND USE.—  A  synthetic  prepara- tion,  hexachlorophene  is  a  bacteriostatic  cleansing agent  most  effective  against  gram  positive organisms.  Pus  or  serum  decrease  the  efficacy. Hexachlorophene is a neurotoxic agent and must not be used on premature infants, denuded skin, burns, or mucous membranes. It is used as an an- tiseptic  scrub  by  physicians,  dentists,  food handlers,  and  others.  Residual  amounts  can  be removed   by   alcohol. Silver Nitrate ACTION  AND  USE.—  The  soluble  salts  of silver  ionize  in  water  to  produce  solutions  that  are astringent  and  antiseptic  in  high  concentration. In  solid  form,  silver  nitrate  is  most  commonly used  to  cauterize  mucous  membranes  or  treat aphthous ulcers. The most common side effect is the skin turns black where the silver nitrate has come into contact with it. This black area is slow to  absorb  but  is  not  harmful.  In  liquid  form,  it is  used  to  prevent  gonorrhea  ophthalmia  in  the newborn (eye drops) or as a wet dressing on burns. Caution must be taken to keep the dressing wet; silver will precipitate from a drying dressing and can  be  absorbed  through  the  skin.  The  effect  is a condition known as agyria, where the skin turns a slate gray. There is no known reversal for this condition. Benzalkonium  Chloride  (Zephiran Chloride) ACTION AND USE.— A somewhat effective, non-injurious surface disinfectant, benzalkonium chloride  is  germicidal  for  a  number  of  gram- positive  and  gram-negative  organisms  including some  fungi.  It  is  inactivated  by  soap  or  alcohol, and is not effective against spores or viral patho- gens.  It  is  most  commonly  used  as  a  cleansing agent  in  animal  bites. Glutaraldehyde (Cidex) ACTION  AND  USE.—   Glutaraldehyde is  effective  against  vegetative  gram-positive, gram-negative,  and  acid-fast  bacteria,  bacterial spores, some fungi, and viruses. It is used in an aqueous solution for sterilization of fiber optics, plastics, rubber, and other materials that are not resistant to heat. Thimersol (Merthiolate) ACTION  AND  USE.—  An  organic  mercury compound, thimersol is non-irritating to the skin and mucus membranes when applied topically. It has   antiseptic,   germicidal,   and   fungicidal properties. Hydrogen Peroxide ACTION   AND   USE.—   Certain   oxidizing agents are destructive to pathogenic organisms but mild  enough  to  be  used  on  living  tissue.  Hydrogen peroxide is a germicide that is active by the release of oxygen. It deteriorates on standing to oxygen and water. It is most commonly used to clean sup- purating  wounds,  and  is  also  efficious  in  the treatment  of  Vincent’s  angina  (trench  mouth).  For external  use  only,  it  is  available  as  a  3  percent solution. ANTIINFECTIVES Antibiotics are chemical compounds produced as  the  result  of  metabolic  activity  of  micro- organisms  or  produced  synthetically.  They  inhibit the growth of susceptible microorganisms or kill them  through  the  destruction  of  necessary  en- zymes. Antibiotics that are sufficiently non-toxic to the host are used as chemotherapeutic agents in  the  treatment  of  infectious  diseases  of  man, animals,  and  plants.  They  can  be  administered orally,  topically,  or  parenterally. Antibacterial Agents The  five  basic  mechanisms  of  action  for  the antimicrobial agents are (1) inhibition of the syn- thesis of the bacterial cell wall, (2) affecting the cell  wall  permeability,  (3)  inhibition  of  protein synthesis  by  affecting  ribosomal  activity,  (4) affecting nucleic acid metabolism, and (5) the anti- metabolites  that  compete  with  necessary  enzymes. To  be  of  practical  value  in  the  treatment  of  in- fection,  an  antimicrobial  agent  must  exert  it  ef- fects  upon  the  invading  microorganism  without seriously  damaging  the  cells  of  the  host.  The following are groups of antimicrobial agents and their  general  mechanisms  of  action. 7-7