Abaloparatide Administration Through the Simplicity Patch: A Therapeutic Option for Refractory Hypoparathyroidism Post-thyroidectomy

Introduction:
Hypoparathyroidism (HPT), characterized by hypocalcemia is typically managed with oral replacement of calcium and vitamin D. Some fail to achieve normocalcemia despite high doses. Such refractory HPT cases have benefited from recombinant PTH (rPTH). Abaloparatide, initially approved for the treatment of osteoporosis, has never been used for refractory HPT. Our case report discusses its administration in refractory HPT through the Simplicity patch.

Case Description:
39 y/o female with iatrogenic HPT failed to achieve normocalcemia despite high doses of vitamin D, calcium supplementation, and rPTH injection. Due to the patient’s recurrent hypocalcemia episodes requiring frequent hospitalizations, we elected to attempt controlling the refractory HPT with a subcutaneous administration of Abaloparatide. A review of the cases that used teriparatide administration through insulin delivery mechanisms was studied meticulously. We opted for Abaloparatide administration via the Simplicity patch. 1 mL of Abaloparatide (equivalent to 2000 mcg) was transferred to the Simplicity patch so that each click administered a 20 mcg dose of Abaloparatide. The patient was closely monitored for 5 days. On day 1, we administered 1 to 2 clicks, spaced 2 hours apart. The patient’s serum calcium levels were carefully monitored with serial calcium profile testing. Over the next 4 days, based on the patient’s response and calcium levels, we created a click-dosing schedule. Her calcium levels were then closely followed weekly for 4 weeks, and monthly thereafter. Two months after the initiation of the therapy, she was able to maintain her calcium levels at 9 mg/dl. Follow-up labs indicated better control of the calcium status and we were able to wean off the oral calcium and vitamin D supplementation by end of 4 months. Four months after initiation of Abaloparatide with the Simplicity patch, she was able to sustain normal calcium levels and reported no hypocalcemic events.

Discussion:
rPTH(1-84) has been approved for the treatment of chronic refractory HPT since 2015. Studies have compared the use of teriparatide for refractory HPT. Administration of teriparatide as divided doses were associated with better control of calcium levels when compared to once-a-day dosing. Higher calcium levels with fewer fluctuations and normal urinary calcium levels were noted in twice-a-day dosing. Several studies have also explored utilizing insulin pumps to administer continuous infusion of rPTH and noted that it was associated with less fluctuation in their serum calcium levels.

Abaloparatide is available as a subcutaneous injection, just like teriparatide. It has never been used for refractory HPT. They have a similar mechanism of action and pharmacokinetics The ease of using the Simplicity patch, allowed us to divide the doses into a customizable click-dosing schedule. Our patient demonstrated a good response to the click-dosing, without any side effects. With the increasing availability of different insulin delivery mechanisms and newer rPTH, there is a need for large-scale trials to further explore the role of Abaloparatide in the management of chronic HPT, using insulin delivery systems.