Doctors say it is time to rethink the use of trimethoprim as empirical treatment for UTIs, with results from an Australian study showing high rates of resistance to the first-line antibiotic.

The UNSW Sydney–led researchers have found that trimethoprim resistance rates range from 20% to 30% of Escherichia coli samples taken from hospitals, aged care facilities and the community.

In contrast, they said resistance to second-line nitrofurantoin was deemed low, while resistance to third-line cefalexin was moderate.

“Although the current Australian Therapeutic Guidelines continue to recommend trimethoprim because of the low risk of adverse outcomes from treatment failure, our data suggest a necessary evaluation of trimethoprim as the first-line therapy for empirical treatment of cystitis,” they wrote.