A study has claimed that at an equal elemental
calcium dose, CaCO3 was not less but equally as efficient in controlling predialysis
hyperphosphatemia as
calcium acetate, provided both
calcium salts were ingested 5 min before meals instead of during meals because the higher acidity of the fasting gastric juice would allow for better dissociation of CaCO3. However, this study did not directly demonstrate that the efficiency of CaCO3 in controlling
hyperphosphatemia was actually greater when it was administered before a meal than during a meal. To examine this point, we performed a 3 month randomized crossover trial in 12 reliable and stable patients maintained on chronic
hemodialysis. Their plasma concentrations of
calcium,
protein,
phosphate,
bicarbonate,
urea, and
creatinine were measured before the first dialysis of each week and the amount of intact
parathyroid hormone (PTH) at the beginning and at the end of each of the 3 months. Comparison of the plasma concentrations measured during the 2 modes of administration showed no significant differences in
creatinine,
urea,
bicarbonate, or intact PTH. The mean (+/-SD) plasma concentration of PO4 was not significantly lower (1.88+/-0.50 vs. 1.74+/-0.41 mM) whereas the corrected level of plasma Ca was significantly lower (2.30+/-0.17 vs. 2.38+/-0.16 mM; p < 0.04) when CaCO3 was given before meals than during meals. In conclusion, the administration of CaCO3 before a meal does not increase its efficiency in controlling
hyperphosphatemia because the level of plasma PO4 was actually slightly higher with this timing of administration whereas the comparison of the
creatinine and
urea levels suggested a stability of
phosphate intake and the comparison of the PTH and
bicarbonate levels suggested the stability of
osteolysis and of the transcellular membrane shift of
phosphate. Also, administration of CaCO3 before a meal is associated with significantly lower plasma corrected
calcium, suggesting less absorption of
calcium, which may be an advantage but only in hypercalcemic patients. There is no reason other than the prevention of its hypercalcemic effect to recommend the administration of CaCO3 just before meals rather than during meals.