The effect of prophylactic trimethoprim on aerobic urinary tract infection during pelvic radiotherapy and the incidence of infections due to fastidious or anaerobic organisms.

A total of 210 patients receiving pelvic radiotherapy were prescribed trimethoprim 200 mg p.o. daily for the duration of radiotherapy. It was prescribed after two mid-stream urine specimens were obtained. Two patients refused to take trimethoprim. The incidence of urinary tract infection prior to starting radiotherapy and trimethoprim was 24% (50 patients). Of these 50 initial infections, eight (16%) were resistant to trimethoprim, necessitating a change to an antibiotic to which the organism was sensitive. Persistent infection occurred in 21 of these 50 patients; 14 (67%) of these infections were resistant to trimethoprim. Of the 160 patients with no initial infection, 25 subsequently developed a urinary tract infection, in spite of prophylactic trimethoprim. Seven of these 25 infections (28%) were resistant to trimethoprim. Prophylactic trimethoprim is not worthwhile for preventing urinary tract infection during pelvic radiotherapy. Eight patients (4%) developed a rash while on trimethoprim, necessitating stopping the drug. Fastidious or anaerobic organisms were isolated in only 15 patients prior to radiotherapy and in seven patients during radiotherapy. Twenty of these 22 patients were female. The organism most commonly isolated was Streptococcus sp. The bacteriuria occurring with these organisms may have resulted from contamination from the vagina.