What is the best course of action for a patient with primary hyperparathyroidism on Sensipar (cinacalcet) 30 mg/day, Monday-Friday, and calcium supplements 500 mg twice a day, with a calcium level of 8.1 and elevated PTH level of 64?

Management of Primary Hyperparathyroidism with Low Calcium on Cinacalcet

Parathyroidectomy is the definitive treatment for this patient with primary hyperparathyroidism who has developed hypocalcemia (calcium 8.1) while on cinacalcet therapy. 1, 2

Current Situation Assessment

The patient presents with:

• Primary hyperparathyroidism (PHPT)
• Elevated PTH of 64 pg/mL
• Low serum calcium of 8.1 mg/dL
• Current treatment: Cinacalcet 30 mg Monday-Friday and calcium supplements 500 mg twice daily

Immediate Management

1. Discontinue cinacalcet therapy

   • Cinacalcet has successfully lowered calcium but has now caused hypocalcemia
   • The FDA label indicates cinacalcet should be withheld if calcium falls below 8.4 mg/dL 2
   • Cinacalcet is only indicated for PHPT when parathyroidectomy would be indicated but cannot be performed 2

2. Adjust calcium supplementation

   • Increase calcium supplementation from 500 mg twice daily to 1000 mg twice daily
   • Monitor serum calcium levels weekly until normalized 1

3. Check vitamin D status

   • Measure 25(OH) vitamin D levels to rule out vitamin D deficiency contributing to secondary hyperparathyroidism 1
   • Consider vitamin D supplementation if deficient

Definitive Management

Refer for parathyroidectomy as the definitive treatment for primary hyperparathyroidism 1

Rationale:

• Parathyroidectomy provides the best outcomes for morbidity, mortality, and quality of life 1
• Cinacalcet provides no measurable clinical benefits for patients with PHPT and may accelerate bone loss with prolonged use 3
• Cinacalcet reduces serum calcium but does not provide symptom relief and more commonly increases subjective symptoms 3

Monitoring Until Surgery

1. Serum calcium monitoring

   • Check serum calcium weekly until normalized
   • Target calcium in normal range (8.5-10.2 mg/dL)

2. PTH monitoring

   • Monitor PTH levels monthly until surgery
   • PTH levels typically remain elevated with cinacalcet therapy 4

3. Bone health assessment

   • Consider bone mineral density testing as prolonged cinacalcet use has been associated with continued bone loss 3

Important Considerations

• Cinacalcet normalizes serum calcium in 75-94% of patients with PHPT but only modestly reduces PTH levels 4, 5
• Long-term cinacalcet therapy has been associated with bone loss in some patients, possibly due to persistent elevated PTH levels 3
• Cinacalcet is not a substitute for definitive surgical treatment in patients who are surgical candidates 1, 3
• The current intermittent dosing schedule (Monday-Friday) may be contributing to fluctuating calcium levels

Caution

• Rapid discontinuation of cinacalcet may lead to rebound hypercalcemia
• Monitor for symptoms of hypocalcemia (paresthesias, muscle cramps, tetany, seizures)
• If severe hypocalcemia develops, consider IV calcium administration

The evidence strongly supports parathyroidectomy as the definitive treatment for this patient, as it provides superior outcomes compared to continued medical management with cinacalcet 1, 3.