A 35-year-old man with a history of penicillin allergy (rash 10 years ago) presents with community-acquired pneumonia. He has a fever of 38.5°C, productive cough, and infiltrates on chest X-ray. Penicillin G is the most effective agent for his organism (Streptococcus pneumoniae), but he reports an allergy. Skin prick testing is negative for penicillin IgE. What is the most appropriate next step in management?