Vetdrugs 2.0Alendronate is an oral nitrogen-containing bisphosphonate that inhibits osteoclast-mediated bone resorption. In veterinary medicine it is used mainly for selected persistent hypercalcemia cases, particularly idiopathic hypercalcemia in cats. Its effect develops through reduced calcium release from bone rather than through immediate removal of calcium from the circulation.
Oral absorption is limited, but absorbed drug binds strongly to mineralized bone and can persist there after plasma concentrations fall. The evidence for adjunctive treatment of neoplastic bone disease is less established than the rationale for controlling excessive bone resorption.
Group
Nitrogen-containing bisphosphonate; inhibitor of bone resorption
Mechanism of Action
Alendronate binds to hydroxyapatite at bone surfaces, especially where active remodeling exposes mineral. Osteoclasts take up the bound drug during resorption, concentrating its action in the cells responsible for breaking down bone.
Within osteoclasts, this nitrogen-containing bisphosphonate inhibits farnesyl diphosphate synthase in the mevalonate pathway. Reduced production of isoprenoid intermediates disrupts prenylation of proteins needed for cytoskeletal organization, vesicle trafficking and osteoclast function. Osteoclast resorptive activity falls, and their survival can also be affected.
Reduced bone resorption decreases the flux of calcium from skeleton into blood, which can lower ionized calcium when excessive skeletal release contributes to hypercalcemia. This does not directly correct every cause of increased calcium, and the persistent bone-bound reservoir explains why its biologic effect can outlast measurable plasma drug.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Hypercalcemia | 0.5–1 mg/kg | PO | Every 24 h | Do not use in: Hypocalcemia, Significant esophageal disease; Give on an empty stomach, follow with water and delay feeding at least 30 minutes. Monitor calcium, phosphorus and renal function. |
| Histiocytic sarcoma complex | Reference only | PO | Investigational description: 70 mg/m² PO daily for fourteen days, then on alternate days for fourteen days, then weekly. The denominator is body surface area, NOT kg; monitor for esophageal injury. The present calculator does not support this unit or staged course. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Persistent ionized hypercalcemia | 5–20 mg/animal | PO | Every 168 h | Do not use in: Hypocalcemia, Significant esophageal disease; Titrate according to serial ionized calcium; 10 mg weekly is a studied starting amount. Give with water on an empty stomach; wait at least 30 minutes before feeding. |
| Persistent ionized hypercalcemia | 2 mg/kg | PO | Every 168 h | Do not use in: Hypocalcemia, Significant esophageal disease; Alternative weight-based weekly starting regimen after dietary management. Follow with at least 6 mL water if swallowing is safe; reassess ionized calcium and phosphorus. Improvement may take 3-4 weeks. |
| Odontoclastic resorptive lesions | 3 mg/kg | PO | Every 12 h | Historical and controversial use for feline odontoclastic resorptive lesions. Preserve this qualification; it is separate from weekly hypercalcemia treatment. |
Indications
- Persistent ionized hypercalcemia in cats, including selected idiopathic cases that remain hypercalcemic despite initial management.
- Selected hypercalcemia associated with malignancy, hyperparathyroidism or vitamin D excess when increased bone resorption contributes to the disorder.
- Adjunctive treatment of selected complications of pathologic bone resorption, including neoplastic bone disease; analgesic and antineoplastic benefits are less well established.
Contraindications
- Hypocalcemia or significant untreated mineral disturbances.
- Esophageal disease, impaired swallowing or inability to ensure passage of the oral dose.
- Renal impairment requires careful assessment because veterinary renal safety data are limited.
- Do not administer concurrently with food, calcium supplements or other products that impair absorption.
Interactions
- Calcium, antacids and other polyvalent-cation products reduce absorption; separate administration.
- Other drugs that irritate the upper gastrointestinal tract may increase local intolerance.
Adverse effects
- Esophageal irritation, erosion or ulceration if a tablet lodges in the esophagus.
- Reduced appetite or gastrointestinal upset.
- Hypocalcemia and hypophosphatemia; marked phosphate depletion can be clinically silent.
- Musculoskeletal pain and jaw osteonecrosis are potential bisphosphonate concerns; the veterinary frequency is not well established.
Toxicity
Excess antiresorptive exposure can cause mineral disturbances, while local contact can injure the esophagus. Monitor ionized calcium, phosphorus and renal function. Administer on an empty stomach with water to ensure swallowing and wait at least 30 minutes before feeding. After a recent oral overdose, do not induce vomiting because of esophageal injury risk. Oral binding with milk or an antacid has been described; this differs from routine administration, when these products reduce desired absorption.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Fosamax 70 mg Tablets Savio Industrial S.r.L. Contains alendronate sodium expressed as 70 mg alendronic acid. This is a human-strength tablet, not a feline unit dose. Store in a tightly closed container at room temperature. | Tablet | 70 mg / tablet | PO |
| Alendronate Sodium Tablets USP 10 mg (Northstar Rx) Aurobindo Pharma Limited Contains alendronate sodium expressed as 10 mg alendronic acid. Store in a tightly closed container at room temperature. | Tablet | 10 mg / tablet | PO |
| Alendronate Sodium Tablets USP 5 mg (Cipla) Cipla Ltd. Strength is expressed as alendronic acid. Store at 20-25 C in a tight, light-resistant container. | Tablet | 5 mg / tablet | PO |
Monitoring and Administration
The drug persists in bone, so biochemical monitoring remains important during prolonged treatment.
Monitor ionized calcium rather than relying only on total calcium, and reassess phosphorus and renal function. Excessive salivation, regurgitation, vomiting or reduced appetite can indicate esophageal or gastrointestinal injury.
Animal reproductive data are limited; adverse fetal and neonatal effects have occurred in rodent studies. The drug's persistence in bone warrants particular caution around breeding.
After absorption, alendronate is taken up by bone or excreted in urine without metabolism. Food and calcium-containing products can markedly reduce its already low oral absorption.
For the described feline hypercalcemia course, give at least 6 mL of water after the tablet to aid esophageal passage; the source also describes butter on the lips to encourage salivation. Response may take 3–4 weeks. Store tablets in well-closed containers at room temperature.