Hi and welcome to HCM,thank you for your query.urinary retention
is caused by obstruction of urinary tract
or insufficient function of bladder. it can be recognized by measuring urine output and by checking creatinine
and urea in blood. also,in this case you would have certain abdominal pain
lower in abdomen. Ondasetron rarely cause retention and i think this is just infection in your case. but if infection recur.you should do more detailed urologic work up.
Wish you good health. Regards