Prolonged hypercalcemia induced by teriparatide: a case report and literature review

Teriparatide is indicated for the treatment of osteoporosis with a high risk of fractures. While transient hypercalcemia is a commonly reported side effect, we report a case of prolonged hypercalcemia associated with teriparatide. The patient was a 76-year-old female who had postmenopausal and glucocorticoid-induced osteoporosis on the background of rheumatoid arthritis since 2005. After failing treatment with etidronate, alendronate, and denosumab in view of minimal improvement in bone density and multiple fragility fractures, she was started on teriparatide on 5 May 2023. Serial serum calcium levels were all normal before the initiation of teriparatide. However, she was noted to have prolonged asymptomatic hypercalcemia after 3 months of teriparatide therapy, with a peak calcium level of 11.78 mg/dl on 27 September 2023. Teriparatide was discontinued since 27 September 2023 and normalization of serum calcium was noted on 31 October 2023.The cumulative effect of teriparatide from relative "overdosing" may be a contributing factor for prolonged hypercalcemia in our case, given she had a body mass index of 14.42 kg/m² but received the standard dose of 20 mcg teriparatide subcutaneously daily. This case underscores the necessity for vigilance in monitoring patients at risk of hypercalcemia during teriparatide therapy. Furthermore, it prompts further investigation into personalized dosing strategies, i.e., in underweight patients.