Principles of antibiotic therapy

Therapeutic Drug Monitoring of Therapy for Infectious Diseases

Optimal use of antimicrobial agents is dependent on a multitude of factors. Empiric therapy should be based on the patient's underlying disease states, the most likely organisms suspected, and susceptibility patterns. Once susceptibilities are known, therapy should be streamlined. A number of factors must be evaluated during therapy. The site of infections must be considered when choosing antimicrobial agents. The minimum inhibitory concentration (MIC) should be evaluated; the antimicrobial agent's MIC should be at or below the breakpoint for the organism to be considered susceptible. Antimicrobial agent selec tion and dosing should take into consideration not only the MIC, but also the post-antibiotic effect, if appli cable. Serum concentrations of antimicrobial agents should be obtained and evaluated to ensure thera peutic levels and to avoid potential toxicities. The choice of an antimicrobial agent is complicated by the emergence of antibiotic resistance. Drug-resistant gram-positive and gram-negative infections are in creasing. We must attempt to control resistance by choosing appropriate antimicrobial agents and maxi mizing dosages. Pharmacists can play a critical role in the management of patients who receive antimi crobial agents.

Antibiotic treatment of sepsis

Early, appropriate antibiotic therapy is critical to the treatment of the septicemic patient. The degree of organ dysfunction, underlying medical conditions, and physiologic abnormalities are important prognostic factors but are not important in initial antibiotic selection. Initial empiric therapy should be directed against the resident flora of the organ, which is primarily involved in the infectious process. Blood cultures should be obtained in all patients for the initiation of antibiotic therapy, and methods should be employed for the early detection of septicemia. Other conditions that mimic sepsis, e.g., pseudosepsis, should be ruled out initially to avoid an incorrect diagnosis and unnecessary antibiotic therapy. Monotherapy and fully recommended doses of antimicrobial drugs delivered by the intravenous route as soon as the diagnosis is established remain the cornerstone of therapy in treating the septic patient. Monotherapy with an antibiotic of the appropriate spectrum is more than adequate to treat the great majority of septicemic patients. Double-drug therapy is recommended to treat febrile leukopenic compromised hosts, serious P. aeruginosa infections, and selected cases of intra-abdominal sepsis. At the present time, corticosteroids and mediator therapy have no place in the treatment of the septic patient.

Therapeutic Drug Monitoring of Therapy for Infectious Diseases

Optimal use of antimicrobial agents is dependent on a multitude of factors. Empiric therapy should be based on the patient's underlying disease states, the most likely organisms suspected, and susceptibility patterns. Once susceptibilities are known, therapy should be streamlined. A number of factors must be evaluated during therapy. The site of infections must be considered when choosing antimicrobial agents. The minimum inhibitory concentration (MIC) should be evaluated ; the antimicrobial agent's MIC should be at or below the breakpoint for the organism to be considered susceptible. Antimicrobial agent selection and dosing should take into consideration not only the MIC, but also the post-antibiotic effect, if applicable. Serum concentrations of antimicrobial agents should be obtained and evaluated to ensure therapeutic levels and to avoid potential toxicities. The choice of an antimicrobial agent is complicated by the emergence of antibiotic resistance. Drug-resistant gram-positive and gram-negative infections are increasing. We must attempt to control resistance by choosing appropriate antimicrobial agents and maximizing dosages. Pharmacists can play a critical role in the management of patients who receive antimicrobial agents.

Tests for bactericidal effects of antimicrobial agents: technical performance and clinical relevance

Bactericidal testing has been used for several decades as a guide for antimicrobial therapy of serious infections. Such testing is most frequently performed when bactericidal antimicrobial agent therapy is considered necessary (such as when treating infectious endocarditis or infection in an immunocompromised host). It has also been used to ensure that the infecting organism is killed by (not tolerant to) usually bactericidal compounds. However, few data are available to support the role of such tests in direct patient care. Several important variables affect the reproducibility of the test results; however, proposed reference methods are now available for performing the MBC test. With minor modifications, these can provide a standardized approach for laboratories that need to perform them. Currently, little evidence is available to support the routine use of such testing for the care of individual patients. However, testing of new (investigational) antimicrobial agents can be beneficial in determining their potential to provide bactericidal antimicrobial activity during clinical use. New methods to assess bactericidal activity are being developed, but as yet none have been rigorously tested in patient care settings; further, for most of these methods, little information is available as to which technical parameters affect their results. In clinical laboratories, all bactericidal tests must be performed with rigorously standardized techniques and adequate controls, bearing in mind the limitations of the currently available test procedures.

Overview of infectious diseases, Part 1

Microbiologic characteristics include virulence, inoculum size, and the interplay between normal flora and pathogenic organisms. These characteristics, as well as relevant host factors, are an important part of the infectious disease process. Parts 2 and 3 of this series will review the use of drug therapy and the general manifestations of infectious diseases.

Dibekacin assay in serum by automated fluorescence polarization immunoassay (Abbott Tdx): Comparison with high-performance liquid chromatography, substrate-labelled fluorescent immunoassay and radioimmunoassay

An immunoassay based on fluorescence polarization detection (FPIA) has been recently adapted for dibekacin. This has been compared with a reference method (high-performance liquid chromatography), and two other methods used in clinical laboratories for monitoring this aminoglycoside, namely substrate-labelled fluorescent immunoassay (SLFIA) and radioimmunoassay (RIA). FPIA was fast and more reliable than SLFIA or RIA, and offered therefore superior performance. However, its nominal cost per assay is high.

Antibiotic penetration in abdominal infection: a case of tobramycin failure responsive to moxalactam

A 50-year-old male developed an Enterobacter cloacae abdominal infection as the result of gangrene of a gastric remnant after gastrectomy. Aggressive antibiotic treatment with tobramycin and clindamycin was instituted, but despite documented in vitro bacterial sensitivity and high serum tobramycin levels, the patient's clinical condition worsened. Enterobacter cloacae continued to grow in the abdominal drainage cultures. As a last resort, moxalactam therapy was started. Within 36 hours, dramatic clinical improvement was seen and Enterobacter disappeared from the abdominal fluid cultures. Antibiotic assays showed that abdominal fluid contained approximately 50 percent of the simultaneous serum moxalactam concentration, while tobramycin was present in abdominal fluid at less than 15 percent of the serum concentration. In spite of bacterial sensitivity to both drugs, it is likely that moxalactam produced better results than did tobramycin, because of better tissue penetration characteristics.