The Effect of Sevelamer Carbonate on Serum Trimethylamine-n-Oxide (TMAO) Level in Patients With Chronic Kidney Disease (CKD) Stage 3b-4

Inclusion Criteria: * 1\. Men or women, aged from 18 to 75 years old; * 2\. Provide informed consent prior to enrolling in the study; * 3\. Estimated glomerular filtration rate (eGFR) between 15-45 ml/min/1.73 m2 (calculated by CKD-EPI equation) Exclusion Criteria: * 1\. Documented poorly controlled diabetes mellitus, poorly controlled hypertension, malignant tumour, or any clinically significant unstable medical condition; * 2\. Active dysphagia or swallowing disorder; or a predisposition to or current bowel obstruction, ileus, or severe gastrointestinal motility disorders including severe constipation; * 3\. Known hypersensitivity to sevelamer or any constituents of the study drug; * 4\. Unable to comply with the requirements of the study; * 5\. Hypophosphatemia (serum phosphorus level \<0.87mmol/L); * 6\. Women who have a positive pregnancy test at enrollment or women who are breast-feeding; * 7\. Have been enrolled in other interventional study; * 8\. Received sevelamer or other intestinal adsorbents, or broad-spectrum antibiotic within one month prior to the screening period.