History of hypersensitivity to penicillins and/or other ingredients. In patients known to be hypersensitive to cephalosporins, potential cross allergenicity should be kept in mind. In diseases like severe pneumonia, empyema, sepsis, pericarditis, meningitis, peritonitis or arthritis requiring high penicillin serum levels, treatment should be started with the water-soluble alkali salt of benzylpenicillin. If neurological involvement cannot be ruled out in patients with congenital syphilis, penicillin dosage forms producing higher CSF concentrations should be used. Special caution should be exercised in patients with an allergic diathesis or with bronchial asthma.