Sevelamer and Secondary Hyperparathyroidism in Chronic Kidney Disease

The Effect of Sevelamer Carbonate on Critical Variables in the Pathogenesis of Secondary Hyperparathyroidism

The hypothesis underlying this study is that phosphate interferes with PTH-mediated calcium reabsorption in the distal nephron and thereby necessitates supranormal [PTH]to maintain normocalcemia in chronic kidney disease. This study will examine the hypothesis with measures of phosphate homeostasis and calcium reabsorption. A double-blind trial of the intestinal phosphate binder sevelamer carbonate will be employed to examine whether reductions in phosphate influx alter distal nephron phosphate concentration and the [PTH] required for calcium reabsorption in the expected manner.

Study Overview

• Status: Completed
• Conditions: Hyperparathyroidism; Chronic Kidney Disease
• Intervention / Treatment: Drug: sevelamer carbonate; Drug: placebo

Detailed Description

The parathyroid hormone concentration ([PTH)] rises as glomerular filtration rate (GFR) falls. This almost universal phenomenon is called secondary hyperparathyroidism (SHPT). [PTH] rises with dietary phosphate in chronic kidney disease. [PTH] also rises with stable dietary phosphate as GFR falls. The mechanism underlying these phenomena is unknown.

We hypothesize that phosphate exerts its effect on [PTH] in the cortical distal nephron (CDN). Ordinarily, intestinal phosphate absorption does not fall in proportion to GFR as chronic kidney disease (CKD) progresses. Consequently, the concentration of phosphate increases in the cortical distal nephron (CDN), where PTH regulates tubular calcium reabsorption. We speculate that increased [P]cdn reduces the concentration of free calcium through complexation, and thereby necessitates high [PTH] for achievement of calcium reabsorption sufficient to maintain normocalcemia. We can show algebraically that [P]cdn is proportional to the ratio EP/Ccr, where EP is the urinary excretion rate of phosphate and Ccr is creatinine clearance, a surrogate for GFR. EP/Ccr can be calculated from measurements in aliquots of serum and urine as [P]u[cr]s/[cr]u. If our hypothesis is correct, we anticipate that [PTH] will be proportional to EP/Ccr in CKD, and that delta [PTH] will be proportional to delta EP/Ccr obtained with sequential determinations.

We will study 30 patients with CKD and a comparable number of controls. All subjects will have normocalcemia. Controls will be seen once for informed consent, and once in the fasting state between 8:00 a.m. and 10:00 a.m. for collection of urine and blood specimens.

Patients with CKD will be seen at five visits at intervals of four weeks. At the first visit, we will obtain informed consent and obtain a specimen for measurement of 25-hydroxyvitamin D (25OHD). At visits 2-5, we will obtain necessary specimens to measure concentrations of PTH, fibroblast growth factor 23 (FGF23), 25OHD, and 1,25-dihyroxyvitamin D (1,25(OH)2D). We will also measure ionized and ultrafilterable calcium, creatinine, and phosphorus in serum and calcium, phosphorus, and creatinine in urine. These measurements will enable us to follow the effects of interventions on hormone concentrations and parameters of calcium and phosphorus homeostasis.

At visit 2 we will prescribe vitamin D in accordance with [25OHD] obtained at visit 1. For [25OHD] < 32 ng/mL, doses will be 50,000 units/d of D2 for one week, followed by 2000 mg/d of D2 for 3 weeks. For [25OHD] > 32 ng/mL, the dose will be D3 2000 mg/d for four weeks. The purpose of this intervention is to minimize the likelihood that vitamin D insufficiency or deficiency contributes to SHPT.

At visit 3, we will instruct patients in a phosphate-restricted diet. At visit 4 we will quantify the metabolic effects of the diet, and will randomly assign patients to receive either placebo or sevelamer carbonate 800 mg tablets, 3 with each meal. At visit 5, we will quantify the effects of the two interventions on parameters of calcium and phosphate homeostasis and on hormone concentrations. We will view positive regressions of [PTH] on EP/Ccr and of ∆[PTH] on ∆EP/Ccr as evidence for our hypothesis.

• Study Type: Interventional
• Enrollment (Actual): 30
• Phase: Phase 3

Contacts and Locations

Study Locations

• United States
  • New York
    • Albany, New York, United States, 12208
      • Stratton Veterans Affairs Medical Center

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 120 years (Adult, Older Adult)
• Accepts Healthy Volunteers: Yes
• Genders Eligible for Study: All

Description

Inclusion Criteria:

• eGFR < 60 ml/min
• age at least 18 years

Exclusion Criteria:

• any primary parathyroid disease

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Quadruple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: sevelamer carbonate; 2400 mg (3 pills) with each meal	Drug: sevelamer carbonate; 2400 mg with each meal for 4 weeks; Other Names: Renvela (Genzyme)
Placebo Comparator: placebo control; 3 placebo tablets with each meal; tablets are identical to sevelamer carbonate 800 mg tablets.	Drug: placebo; 3 tablets with each meal

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Fractional Change in [PTH] in CKD After a 4-week Course of Sevelamer Carbonate	This outcome measure documented the effect of intestinal phosphate-binding on [PTH]. Fractional change was calculated as ([PTH]post - [PTH]pre)/[PTH]pre, where 'pre' and 'post' referred respectively to baseline [PTH] (before treatment) and [PTH] after four weeks of treatment. Reductions were cited as negative numbers, and increments were cited as positive numbers.	4 weeks

Collaborators and Investigators

• Sponsor: Kenneth R. Phelps, M.D.
• Collaborators: Genzyme, a Sanofi Company
• Investigators: Principal Investigator: Kenneth R. Phelps, M.D., Stratton VAMC, Albany, NY

Publications and helpful links

General Publications

• Phelps KR, Mason DL. Parathyroid Hormone, Fibroblast Growth Factor 23, and Parameters of Phosphate Reabsorption. Am J Nephrol. 2018;47(5):343-351. doi: 10.1159/000489270. Epub 2018 May 18.
• Phelps KR, Mason DL, Stote KS. Phosphate homeostasis, parathyroid hormone, and fibroblast growth factor 23 in stages 3 and 4 chronic kidney disease. Clin Nephrol. 2016 May;85(5):251-61. doi: 10.5414/CN108686.
• Phelps KR, Mason DL. Parameters of phosphorus homeostasis at normal and reduced GFR: theoretical considerations. Clin Nephrol. 2015 Mar;83(3):167-76. doi: 10.5414/cn108367.

Study record dates

Study Major Dates

• Study Start: April 1, 2010
• Primary Completion (Actual): August 1, 2012
• Study Completion (Actual): April 1, 2013

Study Registration Dates

• First Submitted: August 27, 2010
• First Submitted That Met QC Criteria: August 30, 2010
• First Posted (Estimate): August 31, 2010

Study Record Updates

• Last Update Posted (Estimate): November 1, 2016
• Last Update Submitted That Met QC Criteria: September 26, 2016
• Last Verified: September 1, 2016

More Information

Terms related to this study

• Keywords: chronic kidney disease; calcium; secondary hyperparathyroidism; phosphate
• Additional Relevant MeSH Terms: Urologic Diseases; Endocrine System Diseases; Renal Insufficiency; Parathyroid Diseases; Kidney Diseases; Renal Insufficiency, Chronic; Hyperparathyroidism; Hyperparathyroidism, Secondary; Molecular Mechanisms of Pharmacological Action; Chelating Agents; Sequestering Agents; Sevelamer
• Other Study ID Numbers: PhelpsK

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO