Urticaria due to calcium pidolate.

Calcium salts are often prescribed in the prevention and treatment of osteoporosis. Adverse reactions have been described, mostly concerning to the gastrointestinal tract, parathyroid glands and bone resorption. We report the case of a 52-year-old woman who started treatment with 500 mg per day of calcium-pidolate. 90 minutes after the intake of the second dose, she experienced an itchy maculopapular eruption. Skin Prick Tests were carried out with the implicated drug and calcium-carbonate and they both were negatives. An oral-challenge-test with 500 mg of calcium-pidolate was ruled out. 60 minutes later, the patient responded positively when she experienced a similar reaction with erythematous and itchy papulae on the trunk and the neck. Finally, an oral-challenge-test with 500 mg calcium-carbonate was performed with good tolerance. To the best of our knowledge, this is the first documented case of allergy to calcium-pidolate with tolerance to other calcium salt.