A 3-year-old boy from rural Maharashtra presents with a 2-day history of fever, irritability, and neck stiffness. On examination, he is febrile (39.2°C), has a positive Kernig sign, and appears acutely ill. CSF analysis shows: WBC 180/μL (90% neutrophils), protein 120 mg/dL, glucose 25 mg/dL (serum glucose 90 mg/dL), and Gram stain reveals pleomorphic gram-negative coccobacilli. Blood and CSF cultures are pending. What is the most appropriate empirical antibiotic regimen for this child?