Gastritis, stomatitis, glossitis, black hairy tongue, indigestions, nausea, vomiting, diarrhea, enterocolitis, pseudomembranous colitis, candidiasis; skin rashes, urticaria; serious & occasional fatal hypersensitivity (anaphylactic) reactions, angioneurotic edema; cross-sensitivity w/ other β-lactams; transient hepatitis, cholestatic jaundice; anemia, thrombocytopenia, thrombocytopenic purpura, eosinophilia, leukopenia & agranulocytosis.