MSRA-1203

A 45-year-old woman presents to her General Practitioner with a 3-day history of increased urinary frequency, urgency, nocturia and mild, lower abdominal discomfort.
On examination, she looks well. She is afebrile, while her abdomen is soft and nontender. A urine dipstick is performed. Her estimated glomerular filtration rate was normal: > 90 ml/minute per 1.73 m2 three months ago.
Urinalysis reveals the following:
Investigation Result
Leukocytes +++
Nitrates +
Blood +
What is the most appropriate initial treatment option?