Alendronate

Generic Name: Alendronate

Brand Names: Fosamax

Alendronate is a bisphosphonate used to treat and prevent osteoporosis by inhibiting bone resorption.

EndocrineOsteoporosisBone Health

Drug Class

Bisphosphonate (Osteoclast Inhibitor)

Pregnancy

Category C (animal studies showed adverse effects on fetal ossification; no adequate human studies — not recommended in pregnancy)

Available Forms

Tablet 5 mg, Tablet 10 mg, Tablet 35 mg, Tablet 40 mg, Tablet 70 mg, Oral solution 70 mg/75 mL, Effervescent tablet 70 mg

What It's Used For

Dosage Quick Reference

These are general dosage guidelines. Your doctor will determine the appropriate dose for your specific situation.

Condition	Starting Dose	Maintenance Dose
Postmenopausal osteoporosis — treatment	10 mg daily or 70 mg weekly	10 mg daily or 70 mg weekly
Postmenopausal osteoporosis — prevention	5 mg daily or 35 mg weekly	5 mg daily or 35 mg weekly
Glucocorticoid-induced osteoporosis	5 mg daily (10 mg daily for postmenopausal women not on estrogen)	5–10 mg daily
Paget's disease of bone	40 mg daily for 6 months	Re-treat if needed after ≥6-month observation period

Side Effects

Common Side Effects:

Abdominal pain
Dyspepsia (heartburn)
Acid regurgitation
Nausea
Constipation
Diarrhea
Flatulence
Musculoskeletal pain
Headache

Serious Side Effects:

Esophagitis and esophageal ulcers
Osteonecrosis of the jaw (ONJ)
Atypical femur fractures
Hypocalcemia
Severe skin reactions (Stevens-Johnson syndrome)
Ocular inflammation (uveitis, scleritis)

Drug Interactions

Calcium supplements, antacids (aluminum, magnesium), and iron: Significantly impair alendronate absorption even in small amounts. Alendronate must be taken at least 30 minutes before any food, drink (except plain water), or other medication.

NSAIDs (e.g., aspirin, ibuprofen, naproxen): Both NSAIDs and bisphosphonates are associated with GI ulceration. Concurrent use increases the risk of esophageal and gastric ulcers. Use with caution, especially in the elderly.

Proton pump inhibitors (PPIs, e.g., omeprazole, pantoprazole): Some studies suggest chronic PPI use may reduce bisphosphonate efficacy and independently increase fracture risk. Others show no interaction. Discuss with your provider if on long-term PPI therapy.

Aspirin: Low-dose aspirin is generally acceptable, but the incidence of upper GI adverse events is increased with concurrent use. Monitor for GI symptoms.

Additional Information

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.

Frequently Asked Questions

Alendronate has very poor oral bioavailability (less than 1%). Even small amounts of food, coffee, juice, or other medications in the stomach can reduce absorption to nearly zero. Taking it first thing in the morning with a full glass of plain water, at least 30 minutes before any food or other medications, ensures adequate absorption.

Alendronate can cause severe esophageal irritation, ulceration, and even erosion if it does not pass quickly to the stomach. Sitting or standing upright and not lying down for at least 30 minutes after taking the tablet (and until after your first food of the day) uses gravity to help the tablet clear the esophagus promptly.

Guidelines suggest reassessing after 3–5 years of therapy. Patients at lower fracture risk may take a "drug holiday" (temporary discontinuation) because alendronate binds to bone for years and maintains some effect after stopping. Patients at high fracture risk (prior vertebral fracture, T-score ≤ -2.5) may benefit from continuing beyond 5 years. Your doctor will reassess periodically.

Osteonecrosis of the jaw (ONJ) is a rare condition where jawbone tissue fails to heal after dental procedures. The risk with oral bisphosphonates like alendronate is very low (estimated 1 in 10,000 to 1 in 100,000 patient-years). The risk is much higher with IV bisphosphonates used for cancer. Good dental hygiene and routine dental care help minimize the risk.

Rarely, long-term bisphosphonate use (usually >5 years) has been associated with atypical subtrochanteric femur fractures. These fractures may be preceded by thigh or groin pain lasting weeks. Report any new thigh pain to your doctor immediately. The overall fracture prevention benefit of alendronate far outweighs this small risk for most patients.

Yes. The 70 mg weekly dose provides equivalent cumulative drug exposure and similar improvement in bone mineral density as the 10 mg daily dose. Most patients prefer the weekly regimen for convenience and potentially fewer GI side effects.

Questions to Ask Your Doctor

Consider discussing these topics at your next appointment:

✓How often should I have bone density (DEXA) scans to monitor my treatment?
✓Is it safe for me to take alendronate given my history of GI problems (reflux, ulcers)?
✓Should I take calcium and vitamin D supplements, and how should I time them with alendronate?
✓After 5 years of treatment, should I consider a bisphosphonate holiday?
✓Do I need to see a dentist before starting alendronate?

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Related Health Conditions

This medication is commonly used to treat or manage the following conditions:

Osteoporosis

Osteoporosis weakens bones due to age, hormonal changes, poor diet, medications, certain medical conditions, and lifestyle factors, increasing fracture risk even from minor incidents.

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Medical Disclaimer: This information is for educational purposes only and should not be considered medical advice. Always consult with your healthcare provider before starting, stopping, or changing any medication. Your doctor can provide personalized recommendations based on your specific health condition and medical history.