After 5 years of use, cefazolin can be considered similar to cephalothin as a therapeutic agent and in its potential for adverse reactions. When cefazolin and cephalothin are compared by appropriately designed clinical trials, neither cefazolin's slightly greater in-vitro susceptibility to staphylococcal beta-lactamase inactivation, nor its slightly greater microbiologic activity for some enterobacteraciae has been shown to result in any readily apparent therapeutic differences. The important differences between cefazolin and cephalothin--and this is also probably true with respect to cephapirin and cephradine--are not in therapeutic effectiveness, microbiologic activity, or toxicity but rather in pharmacokinetics and cost-effectiveness.