The pharmacokinetics of the oral cephalosporins--a review.

The pharmacokinetics of the older and more recent oral cephalosporins are reviewed. With the exception of cefadroxil the older agents (cephalexin, cephradine and cefaclor) have serum elimination half-lives of less than or equal to 1 h and hence have to be administered three to four times daily. The urinary recovery of these agents is high (greater than 80% of oral dose) with the exception of cefaclor (54%). Cefaclor is also chemically unstable. The newer agents can be divided into those that are prodrugs (cefpodoxime proxetil and cefuroxime axetil) and compounds that are absorbed as such (cefixime, cefprozil and ceftibuten). They all have half-lives greater than 1.25 h and can be given once or twice daily. The penetration of these agents into an inflammatory exudate was studied and found to be cefixime 132%, ceftibuten 113%, cefpodoxime 104%, cefuroxime 92% and cefprozil 79% of the serum concentration. The penetration of cefpodoxime and cefixime into the respiratory tract was also studied; the mean percentage bronchial mucosal penetration was 52% for the former and 38% for cefixime. The urinary recovery of these newer agents (with the exception of ceftibuten) tends to be less than that of the earlier agents. There was a relationship between the serum elimination half-life of these agents and the degree of tissue penetration, those agents with longer half-lives penetrating to a greater extent.