Severe Symptomatic Hypocalcaemia Following High-Dose Oral Ibandronate in a Patient With Prior Thyroidectomy and Metastatic Bone Disease

Abstract

Ibandronate is used to treat bony metastatic disease and hypercalcaemia of malignancy. We report the first case of severe hypocalcaemia following oral ibandronate. A 65-year-old woman with widespread sclerotic bony metastases due to breast cancer was commenced on oral ibandronate (50 mg daily). The corrected calcium level decreased from 2.11 mmol / L to 1.38 mmol / L (2.1 - 2.6 mmol / L) accompanied by lower leg muscle cramps 3 weeks after initiation of ibandronate therapy. She had an inappropriately normal PTH level of 6.8 pmol / L (1 - 7 pmol/L) with normal 25-OH vitamin D level of 59 nmol / L and normal magnesium level of 0.88 mmol / L (0.7 - 1.05 mmol / L). There was a history of previous total thyroidectomy for multinodular goitre. Intermittent calcium infusion was required to maintain the corrected calcium level around 1.9 - 2 mmol / L over the next 3 weeks. The patient was discharged on calcium citrate 250 mg tds and calcitriol 0.5 mcg qid with calcium level of 1.96 mmol / L. We conclude that oral bisphosphonates are widely used but rarely associated with symptomatic severe hypocalcaemia. Possible mechanisms in this case include hypoparathyroidism and metastatic bone disease with widespread sclerosis. This case demonstrates that patients may develop symptomatic hypocalcaemia when treated with oral bisphosphonates. doi:10.4021/jem96w