Interaction of microbiology and pharmacokinetics in the selection of appropriate antibiotic therapy

Factors that affect a drug's microbiological activity include drug concentration and duration at the binding site and cell wall penetration. Pharmacokinetics can be used as the basis for substituing one drug for another in some cases. By replacing cefoxitin with cefotetan, our hospital saved $120,000-140,000 a year. Several cephalosporins are compared using microbiological and pharmacokinetic data. For example, the microbiological activity of ceftriaxone lasts for at least 12 hours with Staphylococcus aureus and for almost 24 hours with Enterobacteriaceae. Clinical experience with beta lactams has demonstrated that maintaining serum concentrations above the target organism's minimum concentration required to inhibit 90 percent of the organisms for 50 percent or more of the dosing interval is associated with successful therapy.