PHOSLO GELCAPS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PHOSLO GELCAPS (PHOSLO GELCAPS).
Calcium acetate binds dietary phosphate in the gastrointestinal tract, forming insoluble calcium phosphate complexes that are excreted in feces, thereby reducing serum phosphate levels.
| Metabolism | Calcium acetate is not metabolized; it dissociates in the gastrointestinal tract, and absorbed calcium is excreted renally or incorporated into bone. |
| Excretion | Primarily fecal as unabsorbed calcium; renal excretion accounts for <1% of absorbed dose proportional to glomerular filtration rate. |
| Half-life | Not applicable; calcium is a physiologic ion with dynamic regulation; steady-state serum calcium is maintained by homeostatic mechanisms. In overdose, serum calcium half-life is approximately 3-4 hours. |
| Protein binding | Approximately 40-50% bound to albumin; binding is pH-dependent. |
| Volume of Distribution | Vd of ionized calcium: 0.25 L/kg (distributes primarily in extracellular fluid including plasma and interstitial space). |
| Bioavailability | Oral: Approximately 20-30% of elemental calcium is absorbed in the small intestine via active transport (calcitriol-dependent) and passive diffusion; absorption is dose-dependent and saturable. |
| Onset of Action | Oral: 1-2 hours for increase in serum calcium; phosphate binding occurs within the gastrointestinal tract with immediate onset. |
| Duration of Action | Phosphate binding persists while gelcap remains in the GI tract (approximately 4-6 hours). Serum calcium elevation may last 3-4 hours after absorption. |
| Molecular Weight | 158.17 |
Oral: One to two capsules (668-1336 mg calcium acetate) three times daily with meals, titrated to maintain serum phosphate between 3.5-5.5 mg/dL, maximum 4 capsules per meal.
| Dosage form | CAPSULE |
| Renal impairment | No dose adjustment required based on GFR alone. Use with caution in patients with advanced renal failure due to risk of hypercalcemia; monitor serum calcium and phosphate. |
| Liver impairment | No specific dose adjustment recommended; hepatic impairment does not significantly alter calcium acetate pharmacokinetics. |
| Pediatric use | Not FDA-approved for pediatric use. Limited data: initial 1 capsule (668 mg) three times daily with meals, titrated to target serum phosphate based on age-adjusted norms; monitor closely. |
| Geriatric use | Start at lower end of dosing range (one capsule three times daily with meals); monitor calcium and phosphate levels frequently due to increased risk of hypercalcemia and potential polypharmacy. |
| 1st trimester | Calcium acetate is used as a phosphate binder in chronic kidney disease. No adequate controlled studies in pregnant women. Animal studies not reported. Consider risks vs benefits. |
| 2nd trimester | Same as T1. Limited human data; no known teratogenicity reported. |
| 3rd trimester | Calcium acetate may cause hypercalcemia; monitor maternal calcium levels. Potential risk of neonatal hypocalcemia if maternal hypercalcemia occurs. |
Clinical note
Comprehensive clinical and safety monograph for PHOSLO GELCAPS (PHOSLO GELCAPS).
| Placental transfer | Calcium crosses the placenta via active transport. Degree of transfer from calcium acetate not quantified but expected similar to dietary calcium. |
| Breastfeeding | Calcium is normally present in breast milk. Exogenous calcium acetate likely increases milk calcium but no adverse effects reported in nursing infants. Use caution if maternal hypercalcemia develops. |
■ FDA Black Box Warning
None.
| Serious Effects |
HypercalcemiaHypophosphatemia
| Precautions | Hypercalcemia: Monitor serum calcium levels, especially with concurrent vitamin D or calcium supplements., Digitalis toxicity: Hypercalcemia may potentiate digitalis toxicity; use with caution in patients on cardiac glycosides., Aluminum absorption: Avoid concurrent use with aluminum-containing antacids unless necessary., Gastrointestinal effects: Constipation, nausea, vomiting, and abdominal pain may occur. |
| Food/Dietary | Avoid high-phosphate foods (e.g., dairy, nuts, cola) to enhance efficacy. Do not take with oxalate-rich foods (e.g., spinach, rhubarb) or phytate-containing foods (e.g., whole grains) as they may reduce calcium absorption. |
Loading safety data…
| Lactation Rating | L2 (Probably Compatible) |
| Teratogenic Risk | FDA Pregnancy Category C. No adequate and well-controlled studies in pregnant women. Calcium acetate is not teratogenic in animal studies at doses up to 1.5 times the human dose. Potential fetal effects are indirect via maternal hypocalcemia or hypercalcemia. First trimester: limited data, no known structural anomalies. Second/third trimester: risk of maternal electrolyte disturbances affecting fetal calcium homeostasis. Avoid hypercalcemia which may cause fetal hypocalcemia, tetany, or cardiac effects. |
| Fetal Monitoring | Monitor maternal serum calcium, phosphorus, and calcium-phosphorus product weekly during dose titration and monthly thereafter. Assess for signs of hypercalcemia (anorexia, nausea, vomiting, confusion). Fetal monitoring includes ultrasound for growth and amniotic fluid volume if maternal calcium levels are abnormal. Neonatal calcium levels should be checked at birth if maternal hypercalcemia occurred. |
| Fertility Effects | No known direct effects on fertility. Calcium acetate is used to control hyperphosphatemia in renal disease, which may indirectly affect fertility through improved metabolic control. However, high doses causing maternal hypercalcemia could potentially impair ovulation or implantation; no human data available. |
| Clinical Pearls | Administer with meals to bind dietary phosphate. Monitor serum calcium and phosphate levels regularly. Avoid use in patients with hypercalcemia or calcium-containing kidney stones. Dose titration based on serum phosphate targets. |
| Patient Advice | Take with each meal or immediately after eating to maximize phosphate binding. · Do not crush or chew the gelcaps; swallow whole with water. · Take other medications at least 1 hour before or 2 hours after PhosLo to avoid interactions. · Report symptoms of hypercalcemia: nausea, vomiting, constipation, confusion, or muscle weakness. · Maintain adequate fluid intake as directed by your healthcare provider. |