Blood and Lymphatic System Disorders: Rare (0.01% - 0.1%): Haemolytic anaemia and granulocytopenia (neutropenia), agranulocytosis, leucopenia and thrombocytopenia, have been reported in patients receiving prolonged high doses of benzylpenicillin sodium BP (eg. Subacute bacterial endocarditis).
Immune System Disorders: Very Common (>10%): Patients undergoing treatment for syphilis or neurosyphilis with Benzylpenicillin may develop a Jarisch-Herxheimer reaction. Common (1-10%): Hypersensitivity to penicillin in the form of rashes (all types), fever, and serum sickness may occur (1-10% treated patients). These may be treated with antihistamine drugs. Rare (0.01%-0.1%): More rarely, anaphylactic reactions have been reported (<0.05% treated patients).
Nervous System Disorders: Rare (0.01%-0.1%): Central nervous system toxicity, including convulsions, has been reported with massive doses over 60 g per day and in patients with severe renal impairment.
Renal and Urinary Disorders: Rare (0.01%-0.1%): Interstitial nephritis has been reported after intravenous Benzylpenicillin sodium BP at doses of more than 12 g per day.