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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PHOSLO GELCAPS (PHOSLO GELCAPS).
| Breastfeeding | Calcium is excreted into breast milk, but calcium acetate supplementation is unlikely to significantly alter milk calcium content. The M/P ratio is not established. The drug is considered compatible with breastfeeding when maternal serum calcium is monitored and maintained within normal limits. Use caution if maternal hypercalcemia occurs, as it may suppress lactation or cause neonatal hypercalcemia. |
| 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. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypercalcemia (serum calcium >10.5 mg/dL).","Hypersensitivity to calcium acetate or any component of the formulation.","Concurrent systemic therapy with calcium salts or vitamin D analogs without careful monitoring."]
| 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."] |
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| 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. |