Bone Abstracts

Adverse reactions to bisphosphonates are common and thus, most of them are predictable side effects to the drug. Allergic reactions or skin reactions of any type or severity associated with bisphosphonates have been scarcely described in the literature. Allergic and skin reactions to bisphosphonates have been estimated to occur in less than 1% of patients. The mechanism of these reactions is unknown, although it is presumed to be IgE mediated. All of the bisphosphonates share a similar chemical structure suggesting susceptibility to cross reactivity for immunologically mediated reactions. We report the case of a 5-year-old female patient with Rett syndrome who had a very low bone mass (Z score below -2SD) and experienced a non-traumatic femoral fracture. Spine X-rays showed a vertebral fracture (genant 1). Laboratory measurements were in the normal. It was decided to treat her with bisphosphonates and she received a first intravenous dose of Zoledronic acid (ZOL) with no side effects. However, immediately after the second dose of zoledronic acid infusion, she developed an anaphylactic reaction with major urticarial eruption. She had no previous history of allergic symptoms after tacking any medication. IgE mediation of the reaction was suggested. Prick and intradermal skin testing to pamidronate and zoledronic acid at different concentrations were performed and confirmed by a positive immediate skin test a IgE mediated allergy to zoledronic acid and lack of skin response to pamidronate. A positive skin test response to a non-irritant concentration of a specific bisphosphonate suggested the formation of IgE antibody to that bisphosphonate. She was then treated by IV pamidronate and never presented any skin reaction after then. To our knowledge, this is the first case of skin reaction reported with zoledronic acid.

Disclosure: The authors declared no competing interests.