Role of citric acid in primary hyperparathyroidism with renal lithiasis

Long-Term Safety and Efficacy of Recombinant Human Parathyroid Hormone (1-84) in Adults With Chronic Hypoparathyroidism

Context

Chronic hypoparathyroidism is conventionally treated with oral calcium and active vitamin D to reach and maintain targeted serum calcium and phosphorus levels, but some patients remain inadequately controlled.

Objective

To assess long-term safety and efficacy of recombinant human parathyroid hormone (1-84) (rhPTH(1-84)) treatment.

Methods

This was an open-label extension study at 12 US centers. Adults (n = 49) with chronic hypoparathyroidism were included. The intervention was rhPTH(1-84) for 6 years. The main outcome measures were safety, biochemical measures, oral supplement doses, bone indices.

Results

Thirty-eight patients (77.6%) completed the study. Throughout 72 months, mean albumin-adjusted serum calcium was within 2.00 to 2.25 mmol/L (8.0-9.0 mg/dL). At baseline, 65% of patients with measurements (n = 24/37) were hypercalciuric; of these, 54% (n = 13/24) were normocalciuric at month 72. Mean serum phosphorus declined from 1.6 ± 0.19 mmol/L at baseline (n = 49) to 1.3 ± 0.20 mmol/L at month 72 (n = 36). Mean estimated glomerular filtration rate was stable. rhPTH(1-84)-related adverse events were reported in 51.0% of patients (n = 25/49); all but 1 event were mild/moderate in severity. Mean oral calcium supplementation reduced by 45% ± 113.6% and calcitriol by 74% ± 39.3%. Bone turnover markers declined by month 32 to a plateau above pretreatment values; only aminoterminal propeptide of type 1 collagen remained outside the reference range. Mean bone mineral density z score fell at one-third radius and was stable at other sites.

Conclusion

6 years of rhPTH(1-84) treatment was associated with sustained improvements in biochemical parameters, a reduction in the percentage of patients with hypercalciuria, stable renal function, and decreased supplement requirements. rhPTH(1-84) was well tolerated; no new safety signals were identified.

Hypocitraturia Is an Untoward Side Effect of Synthetic Human Parathyroid Hormone (hPTH) 1-34 Therapy in Hypoparathyroidism That May Increase Renal Morbidity

Subcutaneous human parathyroid hormone (hPTH) therapy can effectively manage hypocalcemia in hypoparathyroidism, with varying effects on hypercalciuria. However, little is known about its ability to decrease the renal comorbidities of hypoparathyroidism: nephrocalcinosis (NC), nephrolithiasis (NL), and renal insufficiency. Urinary citrate (Ucit) promotes the solubility of urinary calcium (UCa); hypocitraturia is a risk factor for NC/NL. Twenty-four-hour UCa, Ucit, and UCa/Ucit were determined in 31 hypoparathyroid subjects receiving hPTH 1-34 therapy for up to 5 years. Before hPTH 1-34, the geometric least squares mean UCa was 346 mg/day (normal <250) and Ucit was 500 mg/day (normal 250-1190); UCa/Ucit was 0.67 mg/mg. After 6 months of hPTH 1-34, UCa decreased (238, p < 0.001), but with a greater decrease in Ucit (268, p < 0.001), increasing UCa/Ucit, which became significant over time (p < 0.001). After stopping hPTH 1-34 and resuming conventional therapy (follow-up; FU), compared to the last measures on hPTH 1-34, Ucit rose to 626 (p < 0.001), reducing UCa/Ucit to 0.44, (p < 0.05); UCa also rose (273), but was still lower than baseline (p < 0.05). Daily hPTH 1-34 dose did not correlate with UCa, but was inversely related to Ucit, and directly related to UCa/Ucit (p < 0.01). Mean blood bicarbonate decreased significantly on hPTH 1-34 and remained lower than baseline at FU (p < 0.01). Mean eGFR increased on hPTH 1-34 (86 to 96 mL/min/1.73 m² , p < 0.001) and returned to baseline at FU. On renal imaging, 6 subjects did not have NC/NL, 8 had NC/NL prior to hPTH 1-34 that remained unchanged, and 16 developed new-onset (n = 10) or progressive (n = 6) NC/NL while on hPTH 1-34. Our data demonstrate that treatment with subcutaneous hPTH 1-34 may have an untoward effect of hypocitraturia and high UCa/Ucit ratio that may increase renal morbidity. With increasing use of PTH therapy in hypoparathyroidism, close monitoring and exploration for treatment of hypocitraturia seem warranted. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Risk factors associated to kidney stones in primary hyperparathyroidism

Nephrolithiasis is the most important clinical manifestation of primary hyperparathyroidism (PHPT), although nowadays this disorder is often asymptomatic. Clinical or biochemical differences between PHPT patients with and without nephrolithiasis have not been clearly identified in most of the previous studies. The aim of the study was to investigate clinical and biochemical parameters in kidney stone former (SF) and non-stone former (NSF) patients with PHPT in order to identify potential risk factors. Serum and plasma samples from 55 consecutive patients (43 females, 12 males) with PHPT were collected after overnight fasting; 24-h urine collection and a fresh sample of urine for sediment analysis were obtained from all patients. Clinical data were recorded in all. Out of 55 patients, 22 had kidney stones, which were symptomatic in 73%. SFs showed circulating PTH, total and ionized calcium, 1,25 dihydroxyvitamin D3, urinary calcium excretion and 24-h urine oxalate levels significantly higher than NSFs. Hypercalciuria was often concomitant with massive quantities of calcium oxalate crystals in urine sediment. Hypercalciuria and relatively high oxaluria were associated with stone formation with an odds ratio (OR) of 4.0 and 7.0, respectively, which rose to 33.5 when they coexisted. Hypomagnesuria and hypocitraturia were common in at least one third of all PHPT patients, but they were not associated to an increased OR. As expected, they were positively correlated with urine calcium excretion, suggesting that calcium, magnesium and citrate are commonly regulated at renal level. In conclusion, hypercalciuria, higher oxalate excretion and severe PHPT are associated with kidney stones in PHPT.