Indications, interpretation and applications of antibiotic assays

Routine monitoring of serum levels is imperative when antibiotics are given to patients with impairment of renal function. Other desirable indications include: need for assessment of adequate aminoglycoside levels in the initial management of severe infection; chloramphenicol therapy; need for control of bioavailability of new drugs or of new derivatives of known compounds; specific clinical situations (unexplained therapeutic failure, assessment of the oral use of antibiotics as an adequate therapy in patient with severe infections; appraisal of the innocuity of topical antibiotics in burned patients or in patients with liver or renal insufficiency). The serum antibacterial test is highly recommended for assessing the adequency of antibiotic therapy in patients with bacterial endocarditis and in infected patients with impaired host resistance such as those with leukopenia. Control of initial treatment in any severe infection, osteomyelitis (particularly when combined antibiotics are used) and tuberculosis are other indications of this test. Any attempt to correlate the results yielded by antibiotic assays with in-vivo effectiveness must take into account the patient himself and the several unknown factors which, in each individual case, can affect the ultimate result of the antibiotic therapy, such as antibiotic delivery to tissues, drug binding to cellular debris, intracellular penetration of the antibiotic, etc.