Prophylactic Chemotherapy

Chemoprophylaxissaket.s.daokar

The basis of effective , true chemoprophylaxis is the use of a drug in an healthy patient to prevent infection by one organism of a certain susceptibility to the administered drug. e.g. Benzylpenicillin against a group A streptococci. It should be used in circumstances in which efficacy is demonstrated and benefits outweigh the risk of prophylaxisCategories in which chemoprophylaxis is recommended:True prevention of a primary infection :- e.g. Rheumatic fever, recurrent urinary tract infections.Prevention of opportunistic infections :- e.g. Due to commensals getting into the wrong place (bacterial endocarditis after surgery and peritonitis after bowel surgery), immunocompromised patients can benefit from chemoprophylaxis.Suppression of existing infection before it causes overt disease :- e.g. tuberculosis , malaria , animal bites , trauma.Prevention of spread among contacts :- e.g. If there is a case of pertussis in the family a nonimmune young fragile child may benefit from erythromycin.

Problems commonly encountered on the use of chemoprophylaxis

Attempts to use prophylactic drugs for pneumonia in the unconscious or in the patients with heart failure , in the newborn after prolonged labour, and in patients with long term urinary catheters have not only failed but have sometimes encouraged infections with less susceptible organisms.Attempts routinely used to prevent bacterial infection secondary to viral infections e.g. in respiratory tract infections measles have not been sufficiently successful to outweigh the disadvantages of drug allergy and infection with drug resistant bacteria.So in these situations it is generally better to be alert for complications and then to treat them vigorously instead of trying to prevent them.

There are two types of chemoprophylaxis:-

Surgical Prophylaxis Nonsurgical ProphylaxisSurgical ProphylaxisSurgical site infections (SSIs) are a major site of nosocomical infections. The estimated annual cost of nosocomical infections in the US is $1.5 billion.General principles of antimicrobial surgical prophylaxis includes:The antibiotic should be effective against common surgical wound pathogen, unnecessarily broad coverage should be avoided as it may lead to resistance.The antibiotic has proved efficacy in the clinical trials.The antibiotic must achieve concentrations greater than the MIC of suspected pathogens, and these concentrations must be present at the time of the incision.The shortest possible course, ie ideally a single dose of the most effective and least toxic antibiotic should be used.The newer broad spectrum antibiotics should be reserved for the therapy of resistant infections.If all the other factors are equal, the least expensive antibiotic should be used.The National Research Council (NRC) wound classification criteria have served as the basis for recommending antimicrobial prophylaxis.

The Study of the efficacy of the Nosocomical Infection Control (SENIC) identified four risk factors for post operative wound infections:Operations on the abdomen.Operations lasting more than 2 hours.Contaminated or the dirty wound classification of the NRC.Surgeries for complications which had 3 medical diagnoses. Patients with at least 2 SENIC risk factors who undergo clean surgical procedures have an increased risk of developing surgical wound infection and must receive antimicrobial prophylaxis.The surgical procedures that necessitate the use of antimicrobial chemoprophylaxis are:Contaminated and clean contaminated operations.Selected operations in which post operative infection may be catastrophic like open heart surgery.Clean procedures that involve placement of prosthetic materials.Any procedures in an immuno-compromised host.

Certain points should be kept in mind before administering prophylactic antimicrobials.Local wound infection patterns should be considered before administering antimicrobials.The selection of vancomycin over cefazolin must be considered in hospitals with high rates of methicillin resistant staph aureus or staph epidermidis infections.In cesarean section antimicrobial is administered after umbilical cord clamping.If short acting drugs like cefoxitin are used then the drug should be re-administered after 3-4 hrs of procedure. Other wise the parenteral administration till the time of incision is sufficient.

Nonsurgical ProphylaxisNonsurgical prophylaxis includes the administration of antimicrobials to prevent colonization or asymptomatic infection as well as the administration of drugs following colonization by or inoculation of pathogens but before the development of disease.Nonsurgical prophylaxis is indicated in individuals who are at high risk for temporary exposure to selected virulent pathogens and in patients who are at increased risk for developing infection because of underlying disease (e.g. immunocompromised hosts).Prophylaxis is most effective when directed against organisms that are predictably susceptible to antimicrobial agents.