Endocrine Abstracts

JOINT2188

Introduction: Intravenous (IV) bisphosphonates can effectively lower calcium levels in primary hyperparathyroidism (PHPT). However, in recurrent severe hypercalcemia, it may be used more frequently than what is ideal. Atypical femur fractures and osteonecrosis of the jaw are reported to be rare side effects from prolonged bisphosphonate use in osteoporosis and the risk is higher with IV compared to oral preparations. Local hospital guidelines recommend IV pamidronate for PHPT patients with severe hypercalcemia. According to the British National Formulary, IV pamidronate can be given at 4-weekly intervals in osteolytic bone metastases, but no similar guidelines exist regarding the number and frequency of infusions for PHPT patients with hypercalcemia. The aim of this single-centre study was to establish the frequency of IV bisphosphonate therapy in these patients and consider subsequent plans for monitoring.

Methods: Patients who had ≥3 pamidronate infusions per year, over the last 3 years (n =19) were reviewed. Concurrent use of cinacalcet and clinical outcomes were analysed. Total infusions per patient was divided by their respective follow-up time (in months, from first IV treatment until surgery or till date) and multiplied by 12 to provide a comparative measure of the equivalent annualised frequency.

Results: All 19 patients were given IV pamidronate for severe hypercalcemia. The dose varied from 30-90mg per infusion. 63.2% (n =12) were on concurrent cinacalcet treatment; 7 patients were completely intolerant to cinacalcet. In 14/19 patients, IV pamidronate was used to manage hypercalcemia whilst waiting for surgery. The other 5 patients opted for a conservative approach for various reasons: lack of localisation and reluctance for open surgery (n =2), failed surgery (n =2) and frailty (n =1). These 5 patients were on cinacalcet but intolerant to higher doses. The mean follow-up time was 13 months (range 4-36 months). Pamidronate use ranged from 3-28 infusions during this time. The average equivalent annualised frequency of infusions was 7/year (range 2-12/year) in this cohort.

Discussion: A small but significant number of PHPT patients needed frequent IV bisphosphonate therapy. Reasons include longer waiting time for surgery (majority of patients), severity of hypercalcemia and intolerance to cinacalcet. The chronic use of pamidronate may increase the risk of atypical side effects in PHPT management too, which is well recognised from osteoporosis experience but less routinely perceived in endocrine clinical practice. This risk should therefore be emphasised (e.g. information leaflets, nurse-led clinics) as part of the counselling process when consenting PHPT patients for longer-term IV bisphosphonate therapy.