The active ingredient in Refzil O is cefprozil, an antibiotic. For a throat infection in an 11-year-old, the correct dosage must be calculated based on her specific body weight rather than her age alone. Typically, the pediatric dosage for throat infections is 15 mg per kilogram of body weight daily, administered for 10 days. Because precise dosing is crucial for her safety and to effectively cure the infection, please consult her paediatrician. They will weigh her to prescribe the exact dose and can also recommend a safe, age-appropriate pain reliever to help soothe her headache.