Susceptibility of obligate anaerobes to trimethoprim-sulfamethoxazole.

Susceptibilities of trimethoprim and sulfamethoxazole were tested alone and in combination (1:20) against 94 isolants of obligate anaerobes from clinical specimens. Ninety percent of the isolants were inhibited by less than 0.25 microgram - less than 4.75 micrograms trimethoprim-sulfamethoxazole/ml; 5.4 micrograms trimethoprim/ml and; 900 micrograms sulfamethoxazole/ml. We concluded that trimethoprim-sulfamethoxazole would be effective in the treatment of infectious processes containing species of obligate anaerobes, including those resistant to the penicillin and cephalothin groups of antibiotics.