Penicillin is a remarkably safe drug, with few adverse effects. Because it is excreted largely unchanged in the urine, it should be administered with caution to the very young and people with impaired renal function. Hypersensitivity reactions (allergies) occur in about 0.1 percent (anaphylaxis) to seven percent (skin reactions) of the population. Allergies to penicillin occur where the degradation products of the drug bind to proteins in the body and become antigenic. This triggers the immune system to produce antibodies, and on subsequent exposures an immune response occurs. When administering the drug an any time, including initially, adequate precautions should be in place to treat for hypersensitivity and anaphylaxis. A high index of suspicion should exist for people with a history of allergy, asthma, hay fever or urticarial (hives).