title: Resistance among fecal flora of patients taking sulfamethoxazole-trimethoprim or trimethoprim alone.
abstract: Because of the widespread occurrence of resistance to sulfonamides among Enterobacteriaceae, some researchers have suggested using trimethoprim (TMP) alone instead of the combination sulfamethoxazole-trimethoprim (SMX-TMP) in treating infections with TMP-susceptible organisms. To answer whether SMX-TMP suppresses the emergence of resistant organisms compared with TMP alone, quantitative fecal cultures were made for total and TMP-resistant organisms before, during, and after SMX-TMP (800/160 mg twice a day) or TMP (200 or 100 mg twice a day) was given to 48 patients for 4 weeks in a prospective, randomized study. All three regimens left anaerobes intact and reduced the total aerobic coliform fecal flora by approximately 4 logs throughout the 4-week treatment period. In 11 of 19 (58%) patients taking TMP 200 mg twice daily, TMP-resistant organisms emerged or increased during therapy (P less than 0.01, compared with none of the 12 controls), whereas in only 4 of 18 (22%) patients on SMX-TMP did TMP-resistant organisms increase. These TMP-resistant organisms increased by less than 1 log and were predominantly Pseudomonas and Acinetobacter species. In only one instance did an SMX-TMP-resistant Escherichia coli strain emerge after 4 weeks of SMX-TMP therapy. The slight increase in Pseudomonas and Acinetobacter species seen with TMP alone in this study raises a potential risk of giving TMP alone in settings where these organisms may cause serious infections, as in immunosuppressed patients.
mesh_terms: D000328:Adult; D001419:Bacteria / Q000187:drug effects*; D004352:Drug Resistance, Microbial; D004359:Drug Therapy, Combination; D004755:Enterobacteriaceae / Q000187:drug effects; D005243:Feces / Q000382:microbiology*; D005260:Female; D006801:Humans; D013420:Sulfamethoxazole / Q000008:administration & dosage* / Q000494:pharmacology; D014295:Trimethoprim / Q000008:administration & dosage* / Q000494:pharmacology; D014552:Urinary Tract Infections / Q000188:drug therapy
chemical_list: D014295:Trimethoprim; D013420:Sulfamethoxazole