Treatment failures with broad-spectrum antibiotics.

Three main reasons for clinical failures of antibiotic therapy are reviewed and discussed: antibiotic resistance, pharmacokinetic properties of the drug used and host factors. Of these, antibiotic resistance is the easiest to study but probably not the most common cause of unsuccessful therapy. Inability of an antibiotic to achieve sufficient concentrations at the site of an infection is most likely also an uncommon reason for lack of response to treatment. In most cases, it seems justified to assume that host factors are the most important explanation when clinical failures of antibiotic therapy are encountered. However, firm data to prove these assumptions are lacking and it is imperative that analysis of failures be included in all clinical trials; in doing such analyses it is likely that considerably more valuable information will be generated than just by analysis of frequencies of favourable therapy outcome.