Alendronate

• Osteoporosis
• Paget's Disease of Bone
• Glucocorticoid-Induced Osteoporosis

Alendronate is a bisphosphonate medication used primarily for the treatment and prevention of osteoporosis. This medication works by inhibiting bone resorption, helping to maintain bone density and reduce the risk of fractures in at-risk populations.

Mechanism of Action

Alendronate belongs to the nitrogen-containing bisphosphonate class and exerts its effects by binding to hydroxyapatite crystals in bone. When osteoclasts attempt to resorb bisphosphonate-containing bone, they internalize the drug, which inhibits farnesyl pyrophosphate synthase, an enzyme in the mevalonate pathway. This inhibition prevents the prenylation of small GTPases essential for osteoclast function, leading to disruption of the osteoclast cytoskeleton, decreased osteoclast activity, and eventually osteoclast apoptosis. The net result is decreased bone resorption, allowing bone formation to exceed resorption and increasing bone mineral density over time.

Available Formulations

Alendronate is available in several formulations to accommodate different dosing schedules. Tablets are available in 5 mg, 10 mg, 35 mg, 40 mg, and 70 mg strengths. An effervescent tablet (70 mg) and oral solution (70 mg/75 mL) are also available for patients who have difficulty swallowing tablets. The 70 mg formulations are designed for once-weekly dosing, improving patient adherence compared to daily regimens.

Medical Uses

Alendronate is indicated for the treatment and prevention of osteoporosis in postmenopausal women, treatment to increase bone mass in men with osteoporosis, treatment of glucocorticoid-induced osteoporosis in patients receiving corticosteroids equivalent to 7.5 mg or more of prednisone daily, and treatment of Paget's disease of bone. Clinical trials have demonstrated significant reductions in vertebral, hip, and other nonvertebral fractures with long-term use.

Dosing Guidelines

For osteoporosis treatment, the recommended dose is 10 mg once daily or 70 mg once weekly. For osteoporosis prevention, 5 mg daily or 35 mg weekly is recommended. For Paget's disease, 40 mg daily for six months is the typical regimen. Alendronate must be taken on an empty stomach, first thing in the morning, with a full glass of plain water (6-8 ounces). Patients must remain upright (sitting or standing) for at least 30 minutes after taking the medication and until after eating their first food of the day. Other beverages, food, and other medications significantly reduce absorption.

Important Safety Information

The most significant safety concerns involve upper gastrointestinal adverse events, including esophagitis, esophageal ulcers, and esophageal strictures. Patients should be instructed to stop the medication and seek medical attention if they develop difficulty swallowing, pain upon swallowing, retrosternal pain, or heartburn. Alendronate is contraindicated in patients with esophageal abnormalities that delay emptying, inability to stand or sit upright for 30 minutes, hypocalcemia, or hypersensitivity to the drug. Osteonecrosis of the jaw and atypical femur fractures have been reported with long-term use.

Drug Interactions

Calcium supplements, antacids, and other divalite cation-containing products significantly reduce alendronate absorption and should be taken at least 30 minutes after alendronate. NSAIDs may increase gastrointestinal irritation risk when combined with alendronate. Proton pump inhibitors may theoretically affect bisphosphonate efficacy, though clinical significance is uncertain. Aspirin products taken concurrently may increase upper gastrointestinal adverse events.

Special Populations

Alendronate is contraindicated during pregnancy due to potential fetal harm. Women of childbearing potential should be advised of the risk, and pregnancy should be avoided during treatment. The medication is not recommended during breastfeeding. Safety and efficacy have not been established in pediatric patients. No dose adjustment is required for elderly patients with normal renal function. Alendronate is not recommended for patients with creatinine clearance less than 35 mL/min. Patients should ensure adequate calcium and vitamin D intake during treatment.