Effect of metronidazole on chronic periodontal disease in subjects using a topically applied chlorhexidine gel

A double blind between subject comparison of the effect of metronidazole and placebo tablets was completed over 22 weeks in 45 subjects with chronic periodontal disease ranging in severity from moderate (PI = 2.0-3.9) to high (PI = 4.0-6.0). All subjects used a topically applied chlorhexidine gel for the first 10 weeks. Throughout the trial plaque, bleeding and calculus were assessed on the buccal, lingual, mesial and distal surfaces of teeth 16, 21, 24, 36, 41 and 44 and their supporting tissues. The pocket depths on the same 4 aspects of all teeth present were measured. The regime employed consisted of oral hygiene instruction (OHI) at the initial visit followed by scaling and further OHI at visits 1 and 2 weeks later. After the third visit 16 X 200 mg metronidazole or placebo tablets were issued with instructions to take 1 that evening and 3 per day at 5-h intervals for the next 5 days. 4 weeks later, scaling and OHI were carried out and the course of test or placebo tablets was repeated. The subjects returned for further scaling and OHI 4 weeks later and the chlorhexidine gel was withdrawn. Final assessments were made 12 weeks later. The results showed that metronidazole had no effect on plaque levels and gingival bleeding beyond the effect of OHI, scaling and chlorhexidine gel. On the other hand, significantly greater reductions in pocket depths were achieved with the use of metronidazole. A surprising and interesting finding was that these reductions were apparent only in the subjects with severe periodontal disease (PI = 4.0-6.0).