The in-vitro activity of doxycycline and minocycline against anaerobic bacteria.

The likelihood of bacterial resistance now prevents the use of oxytetracycline in the empirical therapy of anaerobic infections. This study investigates the in-vitro activity of two semi-synthetic derivatives, doxycycline and minocycline, against a range of anaerobic bacteria. MICs for each antibiotic were determined by an agar incorporation technique. Doxycycline and minocycline were four to eight times more active against the majority of strains than oxytetracycline. With the exception of Bacteroides bivius, almost 90% of strains were inhibited by 4 mg/l of doxycycline or minocycline, but resistance to the same concentration of oxytetracycline was present in 60% of the B. fragilis group, 30% of Peptostreptococcus spp. and 24% of Clostridium perfringens. Doxycycline and minocycline represent an alternative therapy for anaerobic infections where bacterial sensitivities are known.