General principles01.Anti microbials cannot eliminate all micro organisms in the host and cannot prevent all types of infection. hence prophylaxis should be directed against a specific pathogen or used to prevent infection at a specific site
02.Shorter the duration of prophylaxis the larger the range of pathogens affected. For prevention of all infections in leucopoenias
- Broad spectrum anti microbials -> short term
- Long term use-> resistance
- Group “a” strep ->long term use
eg. penicillin for grp.”a” strep->effective not for gonococcus
04.Drugs for therapy may not be good for prophylaxis
eg.penicillin in meningococcal meningitis not effective for prophylaxis
05.Prophylactic drugs should only be used when efficacy has been documented cost, toxicity, superinfection development of resistance
- Antimicrobials must be efffective against majority of organisms causing post.op. infections
- Start therapy 1-2hours before and stop 12-48 hours after op.
- A single pre op.dose gives maximal benefit
- Antimicrobials activity must be present in surgical wound before closure
- Cefazolin ->drug of choice (first generation cephalosporin) 0.5gm -2gm i.v.
- Cefepime 4th generation cephalosporin more resistance to hydrolysis by beta lactamase
eg. enterobacter that may inactivate 3rd generation ceph.
- Very ill patients with infections of unknown origin eg septicaemia anti staph (nafcillin-cloxacillin0 with gm –ve bacilli (gentamicin tobramycin amikacin) immunocompromised
- Mixed infections peritonitis anaerobes– Metronidazole, Gram +ve bacteria- clindamycin coliforms –Aminoglycosides
- Prevent resistance eg : TB (isoniazid,ethambutol,rifampin)
- Enhance effect of single drug eg. sulphonamide with trimethoprim penicillin with aminoglysoide -> enterococcus faecalis