structure and chemical activity. The most impor- tant  mechanism  of  action  of  the  tetracycline  is blocking  the  formation  of  polypeptides  used  in protein  synthesis.  Because  of  their  broad  spectrum of  activity,  tetracycline  are  most  valuable  in  the treatment  of  mixed  infection,  such  as  chronic bronchitis  and  peritonitis;  however,  they  are  drugs of  choice  for  only  a  few  bacterial  infections. Tetracycline is also used as a topical preparation in  the  treatment  of  acne. The  tetracycline  are  relatively  non-toxic,  the most   common   side   effects   being   mild gastrointestinal  disturbances;  allergic  reactions and  anaphylaxis  are  rare.  Administration  to children  and  pregnant  women  is  not  indicated because it may produce discoloration of the teeth and   depress   bone   marrow   growth.   The   major hazard of tetracycline therapy is the overgrowth of  resistant  organisms,  especially  Monilia  and staphylococci. Tetracycline should not be administered with milk,  milk  products,  antacids  or  iron  prepara- tions;  they  combine  with  metal  ions  to  form nonabsorbable  compounds. Tetracycline  Hydrochloride  (Achromycin) ACTION  AND  USE.—  Tetracycline   hydro- chloride (TCN) is used in the treatment of infec- tions   caused   by   Rickettsiae   (Rocky   Mountain spotted  fever,  typhus  fever),  agent  of  lympho- granulomas venereum and granuloma inguinale, and the spirochetal agent of relapsing fever. It is also  indicated  for  certain  gram-negative  micro- organisms.  Tetracycline  hydrochloride  is  indicated for  severe  acne  as  an  adjunctive  therapy.  Food and  some  dairy  products  may  interfere  with  ab- sorption; antacids containing aluminum, calcium, or magnesium impair absorption of the antibiotic as  well.  Give  the  drug  1  hour  before  or  2  hours after  meals. USUAL DOSE.— 1 or 2 grams per day in two or four equal doses, depending on the severity of the  infection. Doxycycline  Hyclate  (Vibramycin) ACTION AND USE.—  Doxycycline  is  active against a wide range of gram-positive and gram- negative  microorganisms  and  has  a  low  affinity for binding with calcium. In addition to the con- ditions  listed  under  tetracycline,  doxycycline  is also indicated for the treatment of uncomplicated chlamydial  infections  and  uncomplicated  gono- coccal    infections. 7-11 USUAL DOSE.— For most uncomplicated in- fections,   200   mg   the   first   day   followed   by   a maintenance dose of 100 mg per day for 7 to 10 days. For venereal diseases, 200 mg per day for 7 days in equally divided doses; for syphilis, 300 mg per day in equally divided doses for 10 days. Intravenous infusion is indicated only when the oral  route  is  not  indicated. Minocycline  Hydrochloride  (Minocin) ACTION  AND  USE.—  Minocycline   hydro- chloride  is  indicated  for  the  same  conditions  as tetracycline   hydrochloride   and   doxycycline hyclate. USUAL DOSE.—  The dosage ranges are the same  as  for  doxycycline  hyclate. AMINOGLYCOSIDES The  aminoglycosides  are  a  group  of  drugs sharing  chemical,  antimicrobial,  pharmacologic, and   toxic   characteristics.   They   are   effective against  most  gram-positive  and  gram-negative organisms; the method of action is by inhibiting protein   synthesis.   Aminoglycosides   can   cause varying degrees of otototicity and nephrotoxicity, depending on the particular agent and the dose. Toxicity  is  more  prevalent  in  the  presence  of  renal impairment,  in  the  very  young  or  old,  dehydra- tion, or with the use of diuretics. Because of their high  toxicity,  they  are  not  recommended  when  the infective  organism  is  susceptible  to  less  toxic preparations. Streptomycin Sulfate ACTION AND USE.—  Streptomycin  sulfate is indicated for all forms of mycobacterium  tuber- culosis; it should be used only in conjunction with other   antituberculosis   drugs,   i.e.,   rifampin   or isoniazid. It is also indicated in the treatment of plague,   tularemia,    chancroid,   granuloma   in- guinale and some urinary tract infections where the infectious agent has shown to be susceptible to streptomycin and not susceptible to less toxic preparations. USUAL DOSE.—  The dosage ranges from 1 to  4  g  daily  depending  on  the  disease  condition and the condition and age of the patient. Strep- tomycin  is  for  intramuscular  use  only.