Question

Explain the specific selection of antimicrobials?

Answer 1

Selection of specific antimicrobials depends upon various factors. They are as follows:

1 .Microbial causing infection.

(A) Accurate diagnosis of causative microbial may not be possible at the outset. Since the microbiological results may not be available before 24-72 hours , an empiric therapy has to be started.

(B) A broad-spectrum Antimicrobial is preferred in a situation where the sensitivity of the microbe to Antimicrobial agents is not known . However when the reports are available a narrow spectrum medicine should be started to avoid toxicity , and also to pinpoint the organism.

(C) A bacteriocidal agent is preferable over bacteriostatic one esp. in severe infections.

(D) Antimicrobial agent will depend on whether the infection is caused by BACTERIA , FUNGI , VIRUS or PARASITE.

(E) In Certain infections like tuberculosis ,a combination therapy is given to prevent resistance against the bacteria.

(F) In Certain severe diseases antimicrobials which have synergetic actions are given eg . Beta-lactams + Aminoglycosides is effective combination against suspected gram +ve and gram -ve infection.

2. Host factors :

(A) Age of patient.: Dosage in extermes of age according to the body weight and renal functions is important.

(B) Severity of morbidity: A broad-spectrum antimicrobial in injectable form is preferred for prompt management of severe infections.

(C) Renal and hepatic functions : certain Antimicrobials are renotoxic and /or hepatotoxic.

(D) Genetic variation .: Certain drugs like Dapsone should not be used in G-6-PD deficiency as it causes hemolysis.

(E) Pregnancy and lactation.: Some Antimicrobials cause fetal defects .

(F) History of allergy to drugs. :If an allergy to a certain drug is known it should not be given. Allergy testing with test dose should be done for Antimicrobials which are notorious for causing allergic reaction eg. Penicillins.

(G) History of recent use of Antimicrobial agent.: If any Antimicrobial has been used in past 3 months ,it should be avoided as there is a possibility of resistance being developed against that organism for which it was prescribed.

3.Other factors :

(A) Cost effective or not.

(B) Toxicity of the Antimicrobial : whether the patient can tolerate the Toxicity of medication.

(C) Selection of Oral or Injectable drug.: This depends on the severity of the disease and if patient is admitted in the hospital or not.