Mr Sampson is a 29 year old patient with Type 1 Diabetes. He has come to see you as he has developed nasal discharge and facial pain. The symptoms started three weeks ago and are not improving. He describes the facial pain as a ‘pressure’ over his forehead and cheeks. The nasal discharge is worst in the morning but present all day and is yellow/green in colour. He has no other systemic symptoms. Mr Sampson reports good diabetic control over the last few weeks (checking his blood sugar four times a day, fasting readings around 5 and post dinner readings around 9-11). Mr Sampson has no other significant medical history; he is a non-smoker and works full-time as a science teacher. He has no known allergies. On examination, tenderness is noted over the maxillary and frontal sinuses. Rhinoscopy identifies mucopurulent discharge and nasal inflammation.
What is the most appropriate treatment?