Introduction
Calcium acetate is a phosphate-binding agent used primarily in the management of hyperphosphatemia in patients with end-stage renal disease. It is classified as a calcium salt that works by binding dietary phosphate in the gastrointestinal tract, forming insoluble calcium phosphate complexes that are excreted in feces rather than absorbed into the bloodstream.
Mechanism of Action
Calcium acetate dissociates in the gastrointestinal tract to release calcium ions (Ca²⁺) which bind with dietary phosphate to form insoluble calcium phosphate complexes (CaHPO₄). This binding process occurs primarily in the small intestine, preventing phosphate absorption into systemic circulation. The insoluble complexes are subsequently excreted in feces, thereby reducing serum phosphate levels.
Indications
- Management of hyperphosphatemia in patients with end-stage renal disease (ESRD)
- Reduction of serum phosphate levels in dialysis patients
- Off-label: May be used as a calcium supplement in specific clinical scenarios (though other formulations are typically preferred)
Dosage and Administration
Standard dosing:- Initial dose: 2-4 tablets (667 mg each) with each meal
- Titration: Adjust dosage gradually to achieve target serum phosphate levels (typically 3.5-5.5 mg/dL)
- Maximum dose: Generally not to exceed 12 tablets daily
- Take with meals to maximize phosphate binding
- Tablets should be chewed or swallowed whole with adequate fluid
- Dosage should be individualized based on serum calcium and phosphate levels
- Renal impairment: Primary indication is for ESRD patients; use with caution in non-dialysis renal impairment
- Hepatic impairment: No dosage adjustment required
- Pediatrics: Safety and efficacy not established
- Geriatrics: No specific dosage adjustment required
Pharmacokinetics
Absorption: Minimal systemic absorption of calcium (approximately 20-30% of administered dose) Distribution: Calcium distributes throughout body tissues; primarily bound to plasma proteins (40-45%) Metabolism: Not metabolized hepatically Elimination: Primarily excreted fecally as insoluble calcium phosphate complexes; absorbed calcium excreted renally Half-life: Not applicable due to local GI actionContraindications
- Hypercalcemia (serum calcium >10.5 mg/dL)
- Patients with calcium-based renal calculi
- Hypersensitivity to calcium acetate or any component of the formulation
- Patients with elevated calcium-phosphate product >55 mg²/dL²
Warnings and Precautions
- Hypercalcemia risk: Monitor serum calcium levels regularly
- Calcification risk: May promote soft tissue calcification if calcium-phosphate product exceeds 55 mg²/dL²
- GI effects: May cause constipation; use with caution in patients with GI motility disorders
- Aluminum toxicity: Avoid concomitant use with aluminum-containing compounds
- Cardiac effects: Use caution in patients receiving digitalis due to potential for arrhythmias
Drug Interactions
- Tetracyclines/fluoroquinolones: Calcium may chelate these antibiotics, reducing their absorption (separate administration by至少 2 hours)
- Levothyroxine: Reduced absorption (separate by至少 4 hours)
- Bisphosphonates: Reduced absorption (separate administration)
- Aluminum/magnesium-containing antacids: Avoid concomitant use
- Digitalis glycosides: Hypercalcemia may potentiate digitalis toxicity
Adverse Effects
Common (≥5%):- Hypercalcemia (mild to moderate)
- Constipation
- Nausea
- vomiting
- Severe hypercalcemia (>12 mg/dL)
- Ectopic calcification
- Calcium-phosphate precipitation
- Bowel obstruction (rare)
Monitoring Parameters
- Serum phosphate levels (monthly initially, then every 3 months when stable)
- Serum calcium levels (monthly)
- Calcium-phosphate product (maintain <55 mg²/dL²)
- Renal function (BUN, creatinine)
- Signs/symptoms of hypercalcemia (constipation, nausea, confusion)
- Nutritional status (albumin, prealbumin)
Patient Education
- Take medication with meals for maximum effectiveness
- Do not take with other medications without consulting healthcare provider
- Report signs of hypercalcemia: nausea, vomiting, constipation, excessive thirst, confusion
- Maintain consistent dietary habits while taking medication
- Regular blood tests are necessary to monitor therapy
- Chew tablets thoroughly or swallow whole with plenty of water
- Inform all healthcare providers about calcium acetate use
References
1. National Kidney Foundation. KDOQI Clinical Practice Guideline for Nutrition in CKD: 2020 Update. Am J Kidney Dis. 2020;76(3 Suppl 1):S1-S107. 2. Block GA, et al. Mineral metabolism, mortality, and morbidity in maintenance hemodialysis. J Am Soc Nephrol. 2004;15(8):2208-2218. 3. Qunibi WY. Comparative effects of iron and calcium carbonate on the efficacy and safety of sevelamer hydrochloride. Kidney Int. 2004;65(3):1069-1079. 4. Goodman WG, et al. Coronary-artery calcification in young adults with end-stage renal disease who are undergoing dialysis. N Engl J Med. 2000;342(20):1478-1483. 5. manufacturer's prescribing information for calcium acetate (PhosLo®) 6. Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline for the Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD). Kidney Int Suppl. 2009;(113):S1-S130.