Clinical Vignette: PTH(1–34) Replacement Therapy in a Child With Hypoparathyroidism Caused by a Sporadic Calcium Receptor Mutation

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Synthetic human PTH 1-34 (hPTH 1-34) replacement therapy in hypoparathyroidism maintains eucalcemia and converts quiescent bone to high-turnover bone. However, the skeletal and metabolic effects of drug discontinuation have not been reported. Nine subjects with hypoparathyroidism received subcutaneous injections of hPTH 1-34 two to three times daily for 19.8 to 61.3 months and then transitioned back to calcium and calcitriol. Biochemistries and bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) were assessed at baseline, while on treatment, and at follow-up 3 to 12 months after drug discontinuation. Two subjects developed hypocalcemia when hPTH 1-34 was abruptly discontinued. Thus, to avoid hypocalcemia, subjects were slowly weaned from hPTH 1-34 over several weeks. When hPTH 1-34 was stopped, subjects were requiring two to three times pretreatment doses of calcitriol and calcium to maintain blood calcium levels. Doses were gradually reduced over many weeks until calcium levels were stable on doses similar to baseline. Bone-specific alkaline phosphatase (BSAP), N-telopeptide (NTX), and osteocalcin (OC) increased significantly with hPTH 1-34; at follow-up, BSAP and NTX had returned to baseline while OC was still slightly elevated. During treatment, BMD was unchanged at the hip and lateral spine but declined at the anterior-posterior (AP) spine, radius, and total body. During weaning, BMD increased, with the hip and lateral spine exceeding pre-hPTH 1-34 values and the whole body returning to baseline. AP spine was increased non-significantly compared to baseline at follow-up. hPTH 1-34 must be gradually weaned in hypoparathyroid patients with high doses of oral medications given to avoid hypocalcemia. The transient increased requirements accompanied by increased BMD after long-term hPTH 1-34 therapy suggest a reversal of the expanded remodeling space favoring bone formation as the skeleton returns to a low-turnover state, reminiscent of the hungry bone syndrome. Further study and close monitoring is required to ensure safe transition to conventional therapy and to elucidate the physiological mechanism of this phenomenon.

Section: Discussionmentioning

confidence: 83%

Transient Increased Calcium and Calcitriol Requirements After Discontinuation of Human Synthetic Parathyroid Hormone 1-34 (hPTH 1-34) Replacement Therapy in Hypoparathyroidism

Gafni

Guthrie

Kelly

et al. 2015

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“…(38)(39)(40)(41)(42)47,85) Winer and colleagues (39) reported no cases of high serum or urinary calcium levels in hypoparathyroid patients treated with teriparatide twice daily over a 3-year period. Data from PTH(1-84) trials showed transient episodes of mild hypercalcemia, accounting for only 4% of all measurements and a significant but minimal and isolated 3-month increase in urinary calcium excretion among 30 subjects receiving the hormone at the dose of 100 mg every other day for 24 months.…”

Section: Safety In Hypoparathyroidism Trialsmentioning

confidence: 99%

Safety of osteoanabolic therapy: A decade of experience

Capriani

Irani

Bilezikian

2012

131

IntroductionO steoporosis is a prevalent disease that affects more than 10 million Americans. The lifetime risk of an osteoporosisrelated fracture is 50% for Caucasian women and 25% for men. Hip fractures carry a 10% to 20% increase in mortality rate within the first year after fracture. (1) The burden of the hip and other fractures can result in chronic pain, disability and other indices of reduced quality of life.Amidst these sobering statistics is the welcome advent over the past two decades of effective pharmacological therapies that reduce fracture risk. The therapies approved for the management of osteoporosis include bisphosphonates, raloxifene (a selective estrogen-receptor modulator), calcitonin, denosumab, strontium ranelate, and parathyroid hormone and PTH(1-84)]. The fulllength PTH molecule and its foreshortened amino-terminal fragment (teriparatide) are currently the only osteoanabolic agents approved for use. PTH(1-84) is not available in the United States. In November, 2002, teriparatide was approved by the U.S. Food and Drug Administration (FDA) for the treatment of postmenopausal osteoporosis and, later, in men. The approval came with restrictions in duration of therapy (18-24 months) and was limited to individuals with advanced osteoporosis at high risk for fracture. Reasons for these limitations relate, at least in part, to the unexpected occurrence of osteosarcoma and other bone neoplasms in Fischer 344 rat toxicity studies. In fact, the pivotal phase 3 trial of teriparatide was suspended when these rat toxicity data became available. The effects on rats was doseand duration-dependent, with rats being treated for approximately 80% of their lifetime and at doses three to 58 times the currently approved human dose. (2) Similar toxicity was seen for PTH(1-84) (3) Given the clear-cut efficacy data when the results of the abbreviated clinical trial results for teriparatide were analyzed, the FDA and equivalent other agencies in Europe and elsewhere granted approval of teriparatide with the stipulations that it should be used for no longer than 2 years. In the United States, the drug carries a ''black box warning'' and contraindicates its use in patients with existing risk factors for osteosarcoma, including Paget's disease of bone, prior skeletal radiation, and children with open epiphyses.Teriparatide has now been used in the United States for 10 years. With a decade of experience, it is timely to review the efficacy and safety profile of this medication. PTH(1-84) will also be reviewed. This perspective will be limited to PTH formulations that are available for the treatment of osteoporosis; we will not be discussing other anabolic agents that are currently being studied but are not yet approved, such as the sclerostin antibody (http://clinicaltrials.gov/ct2/results?term ¼ sclerostin þ anti-þ antibody). PTH mechanisms of actionTeriparatide is an amino-terminal fragment of PTH that is biologically identical to the amino-terminal fragment of human PTH. This fragment contains all the classical bio...

“…However, currently available treatment of hypoparathyroidism by active vitamin D 3 or daily PTH injection frequently causes hypercalciuria and urolithiasis, and none of the available treatments to date can safely control symptoms of ADH patients without renal impairment. (25,49) Therefore, a new modality of therapy is required for ADH patients. Missense activating mutations of CaSR gene cause ADH, (5) and are the main causes of ADH, known as ADH type 1 (ADH1; OMIM# 601198).…”

Section: Discussionmentioning

confidence: 99%

“…(24) Daily injection of PTH has also been studied in ADH patients, and improved hypocalcemia, but did not improve hypercalciuria or nephrocalcinosis. (25) Thus, currently available treatments frequently cause serious complications such as nephrolithiasis and renal impairment, and a new therapeutic approach is needed to correct the hypersensitivity of mutated CaSR to serum Ca in ADH patients.…”

Section: Introductionmentioning

confidence: 99%

Calcilytic Ameliorates Abnormalities of Mutant Calcium-Sensing Receptor (CaSR) Knock-In Mice Mimicking Autosomal Dominant Hypocalcemia (ADH)

Dong

Endo

Ohnishi

et al. 2015

Activating mutations of calcium-sensing receptor (CaSR) cause autosomal dominant hypocalcemia (ADH). ADH patients develop hypocalcemia, hyperphosphatemia, and hypercalciuria, similar to the clinical features of hypoparathyroidism. The current treatment of ADH is similar to the other forms of hypoparathyroidism, using active vitamin D 3 or parathyroid hormone (PTH). However, these treatments aggravate hypercalciuria and renal calcification. Thus, new therapeutic strategies for ADH are needed. Calcilytics are allosteric antagonists of CaSR, and may be effective for the treatment of ADH caused by activating mutations of CaSR. In order to examine the effect of calcilytic JTT-305/MK-5442 on CaSR harboring activating mutations in the extracellular and transmembrane domains in vitro, we first transfected a mutated CaSR gene into HEK cells. JTT-305/MK-5442 suppressed the hypersensitivity to extracellular Ca 2þ of HEK cells transfected with the CaSR gene with activating mutations in the extracellular and transmembrane domains. We then selected two activating mutations locating in the extracellular (C129S) and transmembrane (A843E) domains, and generated two strains of CaSR knock-in mice to build an ADH mouse model. Both mutant mice mimicked almost all the clinical features of human ADH. JTT-305/MK-5442 treatment in vivo increased urinary cAMP excretion, improved serum and urinary calcium and phosphate levels by stimulating endogenous PTH secretion, and prevented renal calcification. In contrast, PTH(1-34) treatment normalized serum calcium and phosphate but could not reduce hypercalciuria or renal calcification. CaSR knock-in mice exhibited low bone turnover due to the deficiency of PTH, and JTT-305/MK-5442 as well as PTH(1-34) increased bone turnover and bone mineral density (BMD) in these mice. These results demonstrate that calcilytics can reverse almost all the phenotypes of ADH including hypercalciuria and renal calcification, and suggest that calcilytics can become a novel therapeutic agent for ADH.