Objectives - A comparative clinical evaluation was designed to investigate the clinical relevance of the usefulnes of metronidazole and spiramycin for the treatment of acute dental infections.Materials and methods - We carried out a prospective, randomized, double blind, multicenter study in adult patients with acute dental infections (acute periapical abscesses, acute cellulitis, pericoronitis, acute necrotic pulp infection, alveolitis). The number of patients was determined in order to demonstrate equivalence between the two regimens. Patients were randomly assigned to clarithromycin (250 mg) b.i.d. or spiramycin (1.5 MIU) + metronidazole (250 mg) b.i.d. for five days.Results - A total of 352 patients were enrolled in the study: 341 (96.9%) were assessable in the intent-to-treat analysis and 321 (91.2%) were assessable per protocol, The clinical success rate at the final visit (10-15 days after end of therapy) was similar in both groups: 92% (clarithromycin) and 95% (metronidazole-spiramycin). Side effects were rare and mild (4.6%) in the clarithromycin group and 5.8% in the metronidazole-spiramycin group (P = not significant). (C) 1999 Elsevier; Paris.