Some aspects of trimethoprim-sulphamethoxazole

Abstract

Results of routine sensitivity testing using discs on Oxoid DST Agar with added lysed horse blood were surveyed, and experiments simulating <i>in vivo</i> conditions in urine performed to assess bactericidal activity. A comparison of <i>in vitro</i> sensitivity studies of urinary pathogens in 1969-1970, before the advent of trimethoprim-sulphamethoxazole (T-S) therapy, with a similar period 2 yr later showed no increase in the number of resistant strains, with the possible exception of Proteus. Claims that all strains of a particular organism were initially sensitive to the combination are usually based on totally insufficient data. Organisms from wound swabs (apart from Pseudomonas), and from 'pus swabs show a similar high percentage of sensitive strains as is found in urinary organisms. Strains of staphylococci are almost universally sensitive and enterobacteriaceae isolated from sources other than urine or faeces have a similar proportion of sensitive strains as is in those from urine. More general use of T-S for soft tissue infections is justified. The development of strains resistant to T-S has been less than that often experienced with other antibacterials after a similar period of widespread clinical use. Soluble sulphonamides should not in general be used except in combination with trimethoprim, since the exhibition of sulphonamides alone readily leads to the emergence of resistant strains, and an increase in the number of such strains might lessen the effectiveness of the more important sulphonamide-trimethoprim combination. These experiments simulating <i>in vivo</i> conditions confirm that T-S is bactericidal, at any rate in urine.