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Sunday, March 15, 2009

CHEMOPROPHYLAXIS (Prophylactic use of Antibiotics)

Large % age of antibiotics is used to prevent the infection rather than treating the established infection. This practice accounts for some of the most flagrant misuse of antibiotics. Generally if the single effective and non-toxic drug is used to prevent infection caused by a specific microorganism or to eradicate infection immediately or soon after, it has become established then chemoprophylaxis is frequently successful.

On the other hand, if the aim of prophylaxis is to prevent colonization or infection by any or all microorganisms present in the environment of the patient, then prophylaxis quite often fail. Prophylaxis may be used to protect healthy persons from acquisition of or invasion by specific microorganisms to which they are exposed.

Success has been established in the following cases.

Penicillin G is used to prevent infection caused by Group A streptococci.

Penicillin G is used to prevent syphilis, gonorrhea in persons after having a contact with infected individual.

The intermittent use of Co-trimoxazole is effective in preventing reoccurrence of urinary tract infection caused by E-coli.

Attempts are often made to prevent secondary bacterial infection in patients who are ill with other diseases. Certain centers have reported a decrease in the incidence of bacterial infections in neutropenic patients given trimethoprim-sulphamethoxazole, although increased number of fungal infections was noted in some cases. The normal microbial flora of the host represents an important defense in the prevention of colonization and infection with various pathogens. “Shotgun” Chemoprophylaxis disrupts this barrier and may be self defeating.

Chemoprophylaxis is recommended to prevent endocarditis in patients with vascular or other structural lesion of heart who are undergoing dental, surgical or other procedure that produces high risk of bacteremia. Any procedure that injures mucous membrane where there are a large number of bacteria will produce transient bacteremia. Streptococci from mouth, enterococci from GIT and genitourinary tract and staphylococci from skin have great propensity to cause endocarditis. Thus chemoprophylaxis is recommended for these microorganisms.

* The most extensive use of chemoprophylaxis is to prevent wound infection after various surgical procedures. For this purpose antibiotic should be administered with in two hours of making the initial surgical incision and may need to be re-administered to maintain consistent effective plasma level of the drug during the procedures. A single pre-operated dose is sufficient prophylaxis for most surgical procedures. Exception includes infected areas, surgery of longer duration and placement of prosthetic implant.

Several factors are important for rational and effective use of antibiotic in such case.

1. Antibiotic must be present at wound site at the time of closure. This demands that drug should be given immediately pre-operatively and if necessary intra operatively.

2. Antibiotic must be effective or active against most likely infected microorganisms. This has prompted the wide use of 1st generation Cephalosporins in this form of Chemoprophylaxis.

3. There is mounting evidence that the continued use of drug after surgical procedure is unwarranted and harmful. The use of antibiotics beyond 24 hours is not only unnecessary but also results in development of more resistant flora and there are more chances of super infection by antibiotic resistant strains.

The risk of toxicity and undue cost of therapy are additional disadvantages.

Chemoprophylaxis is only justified in dirty and contaminated surgical procedures e.g. resection of colon. Also it is indicated where the surgical procedure involves insertion of prosthetic implants.

“It is very important always to keep in mind that systemic use of antibiotics prophylactically does not reduce the need for absolute sterile and skilled surgical techniques.”

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