Yes, Bactrim is commonly used to treat UTIs. The usual adult dosage of Bactrim DS is 1 tablet every 12 hours, or 2 Bactrim tablets every 12 hours. The length of treatment may vary from 3 days to 14 days. Bactrim may also be prescribed to children over 2 months old, and the dosage is based on the child’s weight. Symptom relief is often seen within 3 days of starting treatment.