A 4-year-year-old boy presents with a 3-day history of fever, sore throat, and difficulty swallowing. On examination, his temperature is 38.8°C, he has bilateral tender cervical lymphadenopathy, tonsillar exudates, and palatal petechiae. A rapid antigen detection test (RADT) for Group A Streptococcus is positive. He has no history of penicillin allergy. What is the most appropriate antibiotic treatment according to NICE/PHE guidelines?