C.A. is a 13-year-old female adolescent (weight 56 kg) who presents to the ED with a 1-day history of fever and severe lower right quadrant pain. On examination, she is tearful and reports a pain score of 9/10. She has rebound tenderness when palpating her abdomen. Her temperature is 39.5°C. She has no significant medical history but did begin her menses 3 days ago for the first time. Which is the best initial empiric antibiotic regimen to begin?
a. Cefazolin 1 g intravenously every 8 hours and metronidazole 500 mg intravenously every 8 hours.
b. Ampicillin 2 g intravenously every 8 hours and gentamicin 5 mg/kg/day intravenously every 24 hours.
c. Ceftriaxone 2 g intravenously every 24 hours and tobramycin 5 mg/kg/day every 24 hours.
d. Clindamycin 600 mg intravenously every 8 hours and gentamicin 5 mg/kg/day intravenously every 24 hours.