Effects of penicillin V on the faecal microbiota in patients with pharyngotonsillitis-an observational study.

Following treatment with penicillin V, we observed decreased susceptibility to ampicillin and third-generation cephalosporins, and prolonged colonization with non- Gram-negative species. These findings challenge the perception that penicillin V has limited ecological effect on the intestinal microbiota, and emphasizes the importance of avoiding even narrow-spectrum antimicrobials when possible.