A case of theophylline-induced hypercalcemia

We report a case of theophylline-induced hypercalcemia. The patient, a 51-year-old women, had been administered theophylline for about five years because of bronchial asthma. She was referred to us in March 2003 for the treatment of renal failure and hypercalcemia (15.2mg/dL), which had been increasing since 2001. Clinical and laboratory findings were not consistent with any endocrinopathy. We suspected drug-induced hypercalcemia. Three months after discontinuation of theophylline therapy, the hypercalcemia was completely cured. When admitted to our hospital, the patient was diagnosed as also having Hashimoto's disease. Hyperthyroidism might enhance the effect of theophylline on parathyroid hormone action. Therefore, theophylline induced hypercalcemia even though she was taking the therapeutic level. Moreover, her calcium excretion did not increase despite hypercalcemia. We concluded that her hypercalcemia was induced by theophylline and hyperthyroidism, and that hypocalciuria might have enhanced these conditions.