Endocrine Abstracts

Background: The treatment goal in primary hyperparathyroidism (PHPT) is the achievement of biochemical control and prevention of target organ complications. Parathyroidectomy is the current recommended intervention to cure the disease. However, Cinacalcet is an alternative medical treatment for subgroup of patients in whom surgery is deemed inappropriate, those with recurrent disease, and as bridging therapy for delayed operation particularly in recent COVID pandemic. Current recommended starting dose of Cinacalcet is 60 mg/day, with up titration to a maximum dose of 360 mg/day in divided doses. It is not yet known whether a lower dose of cinacalcet can be effective in controlling hypercalcemia, with the advantage of better tolerability and reduced cost.

Objective: To assess efficacy of Cinacalcet in unselected medically managed patients with PHTH, and to explore minimal effective dose of Cinacalcet required to control hypercalcemia in ordinary clinical practice.

Methods: We conducted a retrospective study including all patients with PHPT who had initiated treatment with cinacalcet at the Endocrinology department over a period of three years. We evaluated pre-treatment baseline biochemical data and subsequent variations at 3^rd, 6^th and 12^thmonth after cinacalcet treatment. As well we assessed effective Cinacalcet dose, treatment side effects, and rate of treatment discontinuation.

Results: Total 66 patients with PHTH (49 women and 17 men, aged 53-97 years) were included. Average baseline serum calcium was 2.95mmol/L (95%confidence interval [CI], 2.92 to 2.98), serum PTH of 17.58±6.514pg/ml, and serum phosphate of 0.83mmol/L (95%CI, 0.80 to 0.86). Following three months of Cinacalcet, serum calcium reduced to average of 2.60mmol/L (95%CI, 2.54 to 2.66) and serum phosphate was up to 0.95mmol/L (95%CI, 0.90 to 1.0). Subsequent measurements at 6- and 12-months’ points were consistent with trend towards eucalcaemia, normalising serum phosphate and stabilising serum PTH level. Sixty seven percent of studied population required Cincalcet dose of 60 mg/day to maintain biochemical eucalcaemia, and further 20% have achieved the desired effects at a dose of 30 mg/day. Among the 66 patients studied, only one discontinued cinacalcet due to intractable GI side effect and one missed follow-up.

Conclusion: Lower than recommended dose of Cinacalcet is effective and well tolerated to control hypercalcaemia of primary hyperparathyroidism. This observation is of clinical significance when the factors of long-term treatment compliance, and targeted elderly population with multiple comorbidities and polypharmacy, are considered. Furthermore, the observation makes Cinacalcet an attractive cost-effective treatment when compared to surgery, and the cost of managing acute and chronic complications of hypercalcaemia.