Acute Allergic Reaction due to Milk Proteins Contaminating Lactose Added to Corticosteroid for Injection

We encountered two patients with severe cow’s milk allergy who reacted strongly to an injection of methylprednisolone sodium succinate (Sol-Medrol 40 mg® Pfizer, Japan). They came to our hospital because of an asthmatic attack or urticaria and were treated with Sol-Medrol 40 mg®. After the injection, the allergic reaction was immediate. Skin prick tests demonstrated that the β-lactoglobulin contaminating the lactose of the drug preparation caused the immediate allergic reaction