Teriparatide is a parathyroid mimetic used in the treatment of severe osteoporosis to increase bone mineral density. Hypercalcaemia is a documented potential adverse effect. We present a unique case in which symptomatic hypocalcaemia and hypomagnesaemia followed initiation of Teriparatide therapy.
PT, a 30-year-old Cambodian female presented to the emergency department with symptomatic hypocalcaemia following commencement of Teriparatide for severe osteoporosis deteriorating despite antiresorptive therapy. Other medical issues included autoimmune hepatitis (cirrhosis and portal hypertension), very low weight (BMI 13.8kg/m2), secondary amenorrhoea, anaemia and intermittent electrolyte and mineral disturbances (hypokalaemia and hyponatraemia). Serum electrolytes and minerals prior to commencing Teriparatide were essentially within normal limits.
Following nine days of initial Teriparatide therapy, PT developed tetany and presented to the emergency department. Her ionised Calcium was 0.99mmol/L, corrected Ca2+ 2.0mmol/L, Mg 0.5mmol/L, PO4 0.85mmol/L, and renal function was normal. Liver function tests were elevated but not significantly different to the patient’s usual levels. A repeat Vitamin D was borderline at 50nmol/L. PT was closely monitored and stabilised with intravenous magnesium, and discharged on calcitriol 0.25mcg daily, magnesium supplementation and ongoing Teriparatide therapy.
Teriparatide is an anabolic bone formation agent, comprising an active fragment of endogenous human PTH and is known to be associated with transient post-dose hypercalcaemia (>2.6). There is currently no literature that has demonstrated Teriparatide therapy being linked with hypocalcaemia or hypomagnesaemia. In fact there is emerging evidence of Teriparatide being used as a treatment for hypoparathyroid-associated hypocalcaemia. It is postulated that Teriparatide may have a converse effect in vulnerable individuals.
This case is the first of its kind in the literature and realises the potential for Teriparatide to cause hypocalcaemia. Given the severity of symptoms, early detection is essential to prevent significant complications.