Serious and occasionally severe or fatal hypersensitivity (anaphylactoid) reactions reported in patients on penicillin therapy, especially with history of β-lactam hypersensitivity, sensitivity to multiple allergens, or previous IgE-mediated reactions (e.g. anaphylaxis, angioedema, urticaria). Use with caution in asthmatic patients. Prolonged use may result in fungal or bacterial superinfection, including C. difficile-associated diarrhea and pseudomembranous colitis. Use with caution in severe hepatic and renal impairment, in neonates (slow drug elimination). Avoid extravasation of I.V. infusions. Penicillins reported to cause apprehension, illusions, hallucinations, depersonalization, agitation, insomnia, and encephalopathy.