Annex 1: Representative Specimen Collection Before Starting Therapy

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It is important to collect adequate and representatives’ specimens from all potentially infected sites prior to the initiation of the antibiotic therapy. Appropriate antibiotic therapy is based on definitive identification of pathogens, which usually requires culture. Once antibiotic therapy has been started, cultures often are rendered sterile, even though viable organisms may remain in the host. It is also important to avoid or minimize contamination by surface contaminants and commensals when collecting specimens.

Monitoring therapeutic response

In many patients, it could be difficult to monitor therapeutic response on clinical grounds alone. However, the subsidence of fever, the return of well-being, and the disappearance of both local and systemic signs of infection in the patient, all signify an appropriate response. Therefore, no further formal monitoring is necessary in most cases. 

An apparent failure to respond clinically may be due to either ineffectiveness of antibiotics (resistance or inappropriate route of administration) or to other reasons e.g. a localized infection that requires a surgical drainage, or a superinfection etc. Careful reassessment is necessary when considering changes of antibiotic therapy. 

In certain situations, measurement of antibiotic activity may be useful in predicting clinical response, e.g. determination of serum bactericidal activity (Schlichter test) in cases of infective endocarditis. 

Assays for drugs with narrow therapeutic: toxic ratio

For antibiotics such as the aminoglycosides and vancomycin, the measurement of their concentration in serum/plasma or other body fluids is often useful to avoid excessive level which are associated with toxicity yet ensure that adequate (therapeutic) levels are achieved. In addition, we often need to consider the renal and hepatic status of the patient while prescribing.