Snapshot A 10-year-old boy presents to his pediatrician for a sore throat. His symptoms began a few days ago and have progressively worsened. He said it's been difficult for him to swallow food and feels feverish. His symptoms are associated with headache and he denies coryza, rhinorrhea, or myalgias. Medical history is unremarkable and he is currently not on any medications. Physical examination demonstrates tonsillar erythema with exudates. A rapid antigen detection test returns positive for Streptococcus pyogenes, and he is started on amoxicillin. (Tonsillopharyngitis) Introduction Medications ampicillin amoxicillin Mechanism of action impairs bacterial cell wall synthesis by binding to penicillin-binding proteins inhibits transpeptidation in bacterial cell wall peptidoglycan synthesis Mechanism of resistance penicillinases Clinical use H. influenzae H. pylori E. coli enterococci Listeria monocytogenes Proteus mirabilis Salmonella Shigella group A strep Adverse effects hypersensitivity reactions rash pseudomembranous colitis