The recall of injectable recombinant parathyroid hormone (PTH; Natpara) in the United States over safety concerns about the product is gravely affecting the lives of American patients with severe hypoparathyroidism who need replacement PTH therapy to adequately control symptoms.
Approximately 2,700 patients in the United States have been affected by the recall of Natpara, according to one of the manufacturers, Takeda. Those who were taking it have had to transition back to controlling their symptoms with just oral medications, including active vitamin D or calcitriol (Rocaltrol) plus calcium supplements, which has had a negative impact on the management of their disease in most cases, with some patients hospitalized because of severe hypocalcemia.
One patient related in an interview that even if the transition from injectable PTH back to calcium supplements and calcitriol goes smoothly, individuals can still feel pretty awful because the benefits of the Natpara are subtle – patients just feel better on it. And one report indicates at least 100 patients who had to stop Natpara because of the Food and Drug Administration recall have been hospitalized.
“It’s been a rough time for all patients previously on Natpara adjusting to oral medications after they have been on a replacement therapy,” endocrinologist Dolores Shoback, MD, University of California, San Francisco, said in an email.
Aliya Khan, MD, agrees: “This molecule ... is life changing ... [It] makes a huge difference in patients’ quality of life and in their ability to function normally.”
“The FDA in the United States made the recall decision, and we have to respect that,” added Dr. Khan, a professor of clinical medicine at McMaster University in Hamilton, Ontario.
“We need to address patients’ needs and [try to] reinstate it,” Dr. Khan added, who is the lead author of recent guidelines on the treatment of hypoparathyroidism and who has received research funding from Takeda and Ascendis Pharma, both of which make injectable PTH.
Dr. Kahn also has advice for U.S. endocrinologists who are having to deal with patients who were previously on Natpara and no longer have access to the drug.
She explains how they can transition patients back to other available therapies.
Oral treatments a 'Band-Aid'
Hypoparathyroidism is a rare endocrine disorder that affects approximately 60,000 people in the United States. The FDA approved Natpara as an orphan drug and as an adjunct to calcium and vitamin D to control hypocalcemia in patients with hypoparathyroidism in January 2015.
The FDA issued the recall for Natpara in September, out of concern that rubber particulate matter originating from the rubber septum of the drug’s cartridge might be contaminating the product.
But the European Medicines Agency, which approved the product under the brand name Natpar in 2017, has not reached the same decision as the FDA; patients in Europe who qualify for injectable PTH still have access to the drug.
As Dr. Khan explained in an interview, PTH is critical for the control of calcium and phosphate homeostasis.
When functioning normally, the parathyroid glands are able to regulate blood calcium levels very finely, sensing how much calcium is being resorbed through the kidney, how much is going in and out of bone, how active vitamin D levels are, and the amount the body is absorbing from the bowel and bone. “It’s all being very carefully fine-tuned continuously,” she said.
Patients with hypoparathyroidism suffer from very low levels of serum calcium, which can, in turn, lead to seizures and cardiac irregularities as well as bronchospasm and even respiratory failure. Magnesium levels can also be dysregulated by hypocalcemia.
“All these are serious results of very low calcium levels,” Dr. Khan emphasized.
These patients “are also not able to eliminate phosphate through the kidneys so their phosphate levels rise,” she added.
Standard treatment for hypoparathyroidism is active vitamin D or calcitriol plus oral calcium supplements.
However, for patients with severe hypoparathyroidism, for whom injectable PTH is indicated, standard treatment is like a “Band-Aid” because what they really need is replacement PTH to help them regulate calcium levels as finely as possible, Dr. Khan said.