MSRA-1859

You are a foundation year 2 Doctor on your GP placement. Your first appointment is 6-year-old Jack. His mother has brought him to see you as he has had a cold over the past 6 days and now has developed a productive cough with green sputum. On examination you hear bilateral crackles at the base of his lungs and there is dullness to percussion at the left base. All basic observations are within normal limits. You diagnose a lower respiratory tract infection and decide to prescribe some antibiotics. Jack has no allergies.
What is the first line antibiotic you would prescribe for Jack?