During the 2016 ATA meetings, I gave a dinner lecture, to endocrinologists, on the use of Natpara on behalf of Shire. Shire is the company that makes this hormone. Natpara is the only FDA approved “bioidentical” parathyroid homone 1-84 that has been approved as an adjunct to vitamin D and calcium for the treatment of patients that are hard to manage with standard therapy which is rocaltrol and calcium supplements. Hypoparathyroidsm happens most frequently as an adverse effect of thyroid or parathyroid surgery. Normally, the parathyroid gland which regulate calcium balance live as four little glands just behind the thyroid. Hypopararthyroid can also occur as a result of autoimmune disease, genetic disease or damage due to radiation or infiltration by excess copper or iron. Parathyroid hormone normally regulates calcium balance by recuperating calcium to the blood from bone and kidney, as well as stimulating the kidney in the conversion of regular vitamin D to its active form so that it can work on the intestines to absorb dietary calcium. Parathyroid hormone also helps the kidney get rid of excess phosphorus. If parathyroid hormone is absent, or deficient, calcium balance cannot be maintained and patients experience low calcium levels in the blood and symptoms related to this such as muscle spasm of hands and feet, tingling around the mouth, and if the calcium drop is rapid or severe then seizures, abnormal heart rhythyms, and spasms of the larynx that can affect ability to breath. As you can gather low calcium is a medical emergency! Our current or standard treatment for this is giving the active form of vitamin D, rocaltrol, which helps adsorb the calcium tablets from the intestines. Other methods of getting calcium from bone or kidney are no longer available without parathyroid hormone. Because the body can no longer get rid of phosphorus normally, the excess phosphorus and calcium can combine to form calcium deposits in various parts of the body including the kidney resulting in kidney damage or kidney stones. Deposits of calcium can also occur in the brain, skin and eyes.
It would be ideal if we had parathyroid hormone as replacement therapy for hypoparathyroidism, however Natpara was not approved as replacement, but as an adjunct to therapy of those that could not be well controlled with standard therapy, this is because rats treated with forteo or natpara at high doses (3-71x the highest doses in humans) developed osteosarcoma or bone tumors. While this may be unique to rats whose skeletons grow their entire lives, and we now have 16,000 patients treated for years with parathyroid hormones 1-34 and 1-84 and osteosarcoma has not been observed, we however cannot still eliminate the potential risk of osteosarcoma for humans with the data we have. So Natpara is not recommended for people with high bone turnovers such as those with Paget’s disease, kids who are growing bones or people who have received radiation to their body (externally or with implants).
I am now treating a few of my hypoparathyroid patients with Natpara. While they are doing well, we are always careful to monitor calcium regularly to avoid high calciums, particularly as we are titrating patients to the right dose, and avoid low calcium if they forget to take the medicine on time or go on a trip forgetting to take the medicine. So I always make sure regular vitamin D levels are normal in the 30-50 range, and my patients need to carry tums and the active form of rocaltrol or calcitriol, just in case.
I recommend that my physician colleagues and patients interested in this topic catch up on the latest publications on this by reading the Special Feature Articles and Position statements on Hypoparathyroidism, in the Journal of Clinical Endocrinology June 2016 issue pages 2273-2324.