Alendronate

Alendronate is an oral bisphosphonate used to reduce osteoclast-mediated bone resorption. Veterinary use includes selected persistent hypercalcemia cases, particularly cats.

Oral absorption is poor and further reduced by food and polyvalent cations. 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.

Group

Nitrogen-containing bisphosphonate; inhibitor of bone resorption

Mechanism of Action

Alendronate binds to mineralized bone and suppresses osteoclast function, reducing calcium release from bone. This can lower calcium in disorders involving increased bone resorption.

Dose Rates

Dogs

Cats

Indications

• Persistent ionized hypercalcemia in cats.
• Selected hypercalcemia associated with malignancy, hyperparathyroidism or vitamin D excess.
• Selected complications of pathologic bone resorption; veterinary evidence varies by condition.

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