600 mg Benzylpenicillin contains 1.68 mmol of sodium. Massive doses of Benzylpenicillin Sodium can cause hypokalaemia and sometimes hypernatraemia. Use of a potassium-sparing diuretic may be helpful. In patients undergoing high-dose treatment for more than 5 days, electrolyte balance, blood counts and renal functions should be monitored.
In the presence of impaired renal function, large doses of penicillin can cause cerebral irritation, convulsions and coma.
Skin sensitisation may occur in persons handling the antibiotic and care should be taken to avoid contact with the substance.
It should be recognised that any patient with a history of allergy, especially to drugs, is more likely to develop a hypersensitivity reaction to penicillin. Patients should be observed for 30 minutes after administration and if an allergic reaction occurs, the drug should be withdrawn and appropriate treatment given.
Delayed absorption from the intramuscular depot may occur in diabetics.
Prolonged use of Benzylpenicillin may occasionally result in an overgrowth of non-susceptible organisms or yeast and patients should be observed carefully for superinfections.
Pseudomembranous colitis should be considered in patients who develop severe and persistent diarrhoea during or after receiving Benzylpenicillin. In this situation, even if Clostridium difficile is only suspected, administration of Benzylpenicillin should be discontinued and appropriate treatment given.