Does Phoslo (calcium acetate) increase calcium levels while decreasing phosphate levels?

Does Phoslo Increase Calcium Levels While Decreasing Phosphate?

Yes, Phoslo (calcium acetate) does increase serum calcium levels while simultaneously decreasing serum phosphate levels, though it causes less hypercalcemia than calcium carbonate at equivalent phosphate-binding doses. 1, 2

Mechanism and Dual Effect

• Calcium acetate contains 25% elemental calcium (167 mg per 667 mg tablet), which is systemically absorbed at approximately 30-40% depending on whether it is taken with or without food 1, 2
• Clinical trials in hemodialysis patients demonstrated that calcium acetate decreased serum phosphorus by 30% over 12 weeks (from 7.4 mg/dL to 5.2 mg/dL, p<0.01) while simultaneously increasing serum calcium by 9% (from 8.9 mg/dL to 9.7 mg/dL, p<0.01) 2
• In a placebo-controlled crossover study, 2 weeks of calcium acetate treatment decreased serum phosphorus by 19% while increasing serum calcium by 7% (both changes statistically significant at p<0.01) 2

Comparative Calcium Effects

• Calcium acetate causes significantly fewer hypercalcemic events compared to calcium carbonate, despite both being calcium-based phosphate binders 1
• Meta-analysis by K/DOQI demonstrated that calcium carbonate led to more hypercalcemic events compared to other phosphate binders, or when directly compared to calcium acetate alone 1
• The key advantage is that calcium acetate binds more than twice as much phosphorus per unit of calcium compared to calcium carbonate (106 mg vs 43 mg phosphorus bound, p<0.05), allowing better phosphorus control with lower calcium doses 3
• When factored for calcium absorption, calcium acetate bound 0.44 mEq phosphate per mEq absorbed calcium compared to only 0.16 mEq phosphate per mEq absorbed calcium with calcium carbonate 3

Clinical Implications for Calcium Balance

• Patients can achieve comparable phosphorus control with calcium acetate using half the amount of elemental calcium compared to calcium carbonate (349 mmol/day vs 699 mmol/day, p<0.001) 4
• Despite using less elemental calcium, the overall incidence of hypercalcemia remains similar between formulations, though patients on concurrent IV calcitriol are at higher risk for hypercalcemia with calcium acetate 4
• K/DOQI guidelines recommend that total elemental calcium intake from diet and phosphate binders should not exceed 2,000 mg/day due to risks of vascular calcification 1
• In real-world practice, 49.2% of patients on calcium acetate and 58.2% on calcium carbonate exceeded 1,500 mg/day elemental calcium intake, with many exceeding 2,000 mg/day 5

Critical Timing Considerations

• Calcium acetate must be taken with meals (10-15 minutes before or during) to maximize phosphate binding and minimize free calcium absorption 1, 2, 6
• When taken with meals, calcium absorption from calcium acetate averages 21%, but increases to 40% when taken while fasting 6
• Taking calcium acetate with meals binds 5.36 mmol of phosphorus, but this drops to only 1.81-2.00 mmol when taken 2 hours after meals or while fasting 6

Common Pitfalls to Avoid

• Do not combine calcium acetate with calcium carbonate as this increases total calcium load and calcium-phosphorus product, raising the risk of vascular and soft tissue calcification 7
• Avoid calcium citrate entirely in CKD patients, as citrate enhances calcium absorption more than other calcium salts 1, 8
• Monitor closely for hypercalcemia when calcium acetate is used with active vitamin D therapy (calcitriol, alfacalcidol), as vitamin D markedly enhances intestinal calcium absorption 1, 4
• If phosphorus control cannot be achieved while keeping elemental calcium intake under 1,500-2,000 mg/day, add a non-calcium phosphate binder (sevelamer or lanthanum carbonate) rather than increasing calcium acetate dose 1, 8