The present study revealed that minimum inhibitory concentrations (MICs) of trimethoprim (TMP) alone against various strains of Staphylococci and Gram-negative rods (except for Pseudomonas) in vitro were significantly superior to those of sulfamethoxazole (SMX) alone. Few strains were found to be resistant to TMP, however. When SMX was combined with TMP in a ratio of 20 : 1, MICs were found to be 1 to 2 fold higher than that of TMP alone, but its antibacterial spectrum became broader. The implication of this phenomenon was discussed in relation to the therapeutic practice.
Clinical trials with this combination product revealed that 21 out of 26 patients with respiratory tract infection, and 4 out of 6 patients with urinary tract infection responded, efficacy rates of 80.8% and 66.7%, respectively. All responders belonged to infections of less than moderate severity. Although further clinical experience is in order, this product seems to be indicated for infections of moderate and mild severity. It was of particular interest to note that 6 of 8 non-responders to SMX alone were classified as responders after the therapy with SMX-TMP combination product. Six out of 35 cases complained of gastro-intestinal disturbance; all but I were mild and necessitated no interruption of the treatment. No haematological side effects have been observed.
