The main side effect of cephalosporins is hypersensitivity (drug allergy). Penicillin-sensitive patients also have allergic reactions to the cephalosporins, depending on the cephalosporin generation. Allergic reactions may manifest as e.g. skin rash, pruritus (itching), urticaria, serum sickness-like reactions with skin rash, fever and arthralgia as well as anaphylaxis.
Other side effects include gastrointestinal disturbances (e.g., diarrhea, nausea and vomiting, abdominal discomfort, liver enzyme disturbances, transient hepatitis, and cholestatic jaundice), headache, and Stevens-Johnson syndrome.
Rare adverse reactions include eosinophilia and blood disorders (including thrombocytopenia, leukopenia, agranulocytosis, aplastic anemia, and hemolytic anemia); reversible interstitial nephritis; hyperactivity, nervousness, sleep disturbances, hallucinations, confusion, hypertension, and dizziness.
Symptoms of overdose include diarrhea, nausea, stomach upset, and vomiting.