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Muanda FT, Sheehy O et al. CMAJ 2017;189: 625–633

After taking into account for potential confounders, use of azithromycin (odds ratio [OR] 1.65, 95% confidence interval [CI] 1.34–2.02,), clarithromycin (OR 2.35, CI 1.90–2.91), metronidazole (OR 1.70, CI 1.27–2.26), among other antimicrobials, were associated with an increased risk of spontaneous abortion. The dental use of clarithromycin, which is active against beta-lactamase-producing bacteria, offers no advantage when compared with first line antibiotics used in dentistry (http://www.sdcep.org.uk/wp-content/uploads/2016/03/SDCEP-Drug-Prescribing-for-Dentistry-3rd-edition.pdf). However, azithromycin, a macrolide, may have a role for those patients with a sub-optimal response to conventional periodontal therapy, and in the treatment of cyclosporine-induced gingival overgrowth. Metronidazole is a suitable alternative for those dental patients who are allergic to penicillin. This was a nested case-control study (in this study for each abortion, ten controls were randomly selected and matched by gestational age and year of pregnancy) using data from the Quebec Pregnancy Cohort (1998–2009).