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Cephalexin was compared with ampicillin in the treatment of urinary tract infections by a random double-blind technique. Both drugs were found to be equally effective. In 21 out of 31 patients treated with cephalexin and in 20 out of 31 treated with ampicillin the urine was sterile three weeks after starting therapy. The bacteriological findings at one and eight weeks were also similar in both groups. No serious adverse reactions were attributable to cephalexin, which seemed to be tolerated rather better than ampicillin.

A multicentre prospective study of 933 patients being treated with ampicillin showed a rash incidence of 7.3%. The rash was commonest in women and patients suffering from viral infections. Most rashes were maculopapular and were not associated with features of true penicillin allergy. We conclude that the development of a maculopapular rash during or after treatment with ampicillin is not in itself a contraindication to future treatment with the penicillins.

Purification of ampicillin (Penbritin) with respect to protein impurities has been found significantly to reduce the incidence of rashes in treated patients. This may be related to findings in animals that injections of the isolated protein impurity can induce the formation of circulating IgG antibodies and skin-sensitizing antibodies.