title: In vitro phosphate-binding ability of calcium-based agents is augmented by co-administration of activated charcoal.
abstract: BACKGROUND
  Calcium carbonate is widely used as a phosphate binder in patients on maintenance hemodialysis. An unwanted side effect of calcium carbonate is hypercalcemia and vascular calcification. Oral activated charcoal (AC) is a non-selective and highly effective adsorbent. We hypothesized that AC augments the phosphate binding capacity of calcium-based agents. We performed an in vitro study to test this hypothesis.
  
  
  METHODS
  Simulated gastric fluid and intestinal fluid were prepared with a phosphate concentration of 10 mmol/l. Different dosages of calcium chloride (0.083 g, 0.167 g, and 0.250 g), AC (0.15 g, 0.30 g, and 0.45 g) or a combination of both were added to either gastric or intestinal fluid for phosphate binding. After a reaction time of 2 hours, phosphate concentrations in the supernatant were measured, and absolute reduction and percent reduction of phosphate were calculated. The phosphate-binding abilities of calcium chloride, AC, and a combination of both were compared.
  
  
  RESULTS
  In simulated intestinal fluid there was no significant difference in the percent reduction of phosphate concentrations among the different calcium chloride concentration groups (28.90 ± 2.04 vs. 33.33 ± 3.90 vs. 31.86 ± 5.23) and there was still no significant difference in phosphate concentrations among the different AC groups (3.33 ± 0.08 vs. 3.26 ± 0.01 vs. 3.36 ± 0.11). In simulated gastric fluid phosphate concentrations at each of the time points (before the reaction, 1 hour after calcium chloride was added, and 2 hours after AC was added) were not significantly different. In simulated intestinal fluid the percent decrease in phosphate concentration in the calcium chloride + AC group was significantly higher than that in the calcium chloride group (48.23 ± 5.55 vs. 30.72 ± 6.11).
  
  
  CONCLUSIONS
  AC alone had no phosphate-binding ability in either gastric or intestinal fluid. The phosphate-binding ability of calcium chloride was improved by AC in intestinal fluid.
authors.affiliation: Renal Division, Department of Medicine, Peking University First Hospital, Beijing, China.
authors.forename: Meng
authors.initials: M
authors.lastname: Jia
authors.forename: Xu-Yang
authors.initials: XY
authors.lastname: Cheng
authors.forename: Li
authors.initials: L
authors.lastname: Zuo
mesh_terms: D000931:Antidotes / Q000008:administration & dosage*; D001826:Body Fluids; D002122:Calcium Chloride / Q000737:chemistry*; D002606:Charcoal / Q000008:administration & dosage*; D005750:Gastric Juice / Q000737:chemistry*; D006801:Humans; D006934:Hypercalcemia / Q000517:prevention & control; D066298:In Vitro Techniques; D007419:Intestinal Secretions / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D006435:Renal Dialysis / Q000009:adverse effects; D013997:Time Factors
chemical_list: D000931:Antidotes; D010710:Phosphates; D002606:Charcoal; D002122:Calcium Chloride