Trimethoprim/sulfamethoxazole has been suggested as a treatment option for chronic rhinosinusitis with purulence. This study aimed to assess the functional and endoscopic outcomes after a three-month course of low-dose trimethoprim/sulfamethoxazole.

A prospective study was performed, comprising patients referred to a tertiary care medical centre with a diagnosis of chronic rhinosinusitis with purulence. Trimethoprim/sulfamethoxazole was prescribed at 960 mg/day for three months. Sinonasal complaints and endoscopic findings were documented, and bacteriological data were compared.

Fifteen patients were included. Staphylococcus aureus was the most common bacterium cultured (86 per cent). Improvement in nasal function, as measured by the 22-item Sino-Nasal Outcome Test, was highly significant at three months (p < 0.0005). This improvement slightly decreased but remained significant at 6, 9 and 12 months. No side effects were noted. Endoscopic scores revealed similar and concordant improvements.

Long-term low-dose trimethoprim/sulfamethoxazole therapy seems to be a safe option for selected patients. Additional randomised multicentre studies remain necessary.