A 5-year-year-old child presents with a 3-day history of fever, sore throat, and difficulty swallowing. On examination, temperature is 39.0°C, tonsils are enlarged and erythematous with exudates, and tender cervical lymphadenopathy is present. A rapid antigen detection test for Group A Streptococcus is positive. According to NICE NG84, what is the recommended first-line antibiotic treatment?