Cephalexin, a semisynthetic cephalosporin antibiotic, has wide clinical application in respiratory infections of children and adults. In pharyngitis and tonsillitis due to beta-haemolytic streptococci, it is comparable to penicillin, cyclocillin, and cephaloglycin, as measured by clinical response, bacteriological cure rate, and incidence of relapse and reinfection. In otitis media, it is effective at dosages of 50-100 mg/kg/day except in those infections caused by Haemophilus influenzae, in which there is failure in 50% of the cases. In other infections of the upper respiratory tract, it appears to be effective except, again, in those caused by H. influenzae. Dosages of 1-2 g/day have been used in adults and 20-100 mg/kg/day in children. Adverse effects, mostly gastrointestinal upsets, rash, and urticaria, have been relatively infrequent and have not required discontinuance of the drug.