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Alendronic Acid

Alendronic Acid

Fosamax Binosto Alendros Alendron Alenmax

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Updated: December 06, 2025

Overview

Alendronic Acid is a nitrogen-containing bisphosphonate that inhibits osteoclast-mediated bone resorption. It is widely used in the management of osteoporosis and other metabolic bone disorders. By reducing bone turnover, it helps maintain bone mineral density and decreases fracture risk. The drug has demonstrated significant efficacy in postmenopausal osteoporosis, glucocorticoid-induced osteoporosis, and Paget's disease of bone. Its therapeutic effects are sustained with long-term use, though optimal results require proper administration and adherence to dosing guidelines.

Drug Class

Bisphosphonate (nitrogen-containing) Therapeutic category: Antiresorptive agent ATC code: M05BA04

Mechanism of Action

Inhibits farnesyl pyrophosphate synthase in osteoclasts, disrupting the mevalonate pathway Prevents protein prenylation required for osteoclast function Induces osteoclast apoptosis Reduces bone resorption and turnover Increases bone mineral density by maintaining the bone matrix

Pharmacokinetics

Absorption: Poor oral bioavailability (0.6-0.8%), significantly reduced with food/drink Distribution: Approximately 50% binds to exposed bone mineral surfaces Metabolism: Not metabolized systemically Excretion: Primarily renal (unchanged drug) Half-life: Plasma: 0.5-1 hour; Bone: >10 years (reflects skeletal binding)

Pharmacodynamics

Reduces bone turnover markers (urinary N-telopeptide, serum CTX) Increases bone mineral density (BMD) at spine and hip Decreases vertebral and non-vertebral fracture risk Effects persist for months after discontinuation

Indications

• Treatment of postmenopausal osteoporosis (reduces fracture risk) • Prevention of postmenopausal osteoporosis in high-risk women • Treatment of glucocorticoid-induced osteoporosis in men and women • Treatment of Paget's disease of bone (off-label in some regions) • Treatment of osteoporosis in men

Contraindications

Absolute: • Abnormalities of the esophagus (stricture, achalasia) • Hypocalcemia • Severe renal impairment (CrCl <35 mL/min) • Inability to stand/sit upright for 30 minutes Relative: • Active upper GI disorders (dysphagia, esophagitis) • Mild-moderate renal impairment (CrCl 35-60 mL/min) • Concurrent NSAID use

Dosage & Administration

Postmenopausal osteoporosis (treatment): 10 mg daily or 70 mg weekly orally Postmenopausal osteoporosis (prevention): 5 mg daily or 35 mg weekly orally Glucocorticoid-induced osteoporosis: 5 mg daily (postmenopausal women not receiving estrogen: 10 mg daily) Paget's disease: 40 mg daily for 6 months (may repeat after 6-month drug holiday)

Special Populations

Pediatric: Safety and efficacy not established Geriatric: No dosage adjustment needed but increased risk of renal impairment Renal impairment: Avoid if CrCl <35 mL/min; use caution in moderate impairment Hepatic impairment: No dosage adjustment required

Adverse Effects

Common (>10%): • Gastrointestinal: Dyspepsia, abdominal pain, nausea • Musculoskeletal: Musculoskeletal pain Serious (<1%): • Osteonecrosis of the jaw • Atypical femoral fractures • Severe esophageal irritation/ulceration • Hypocalcemia • Uveitis/scleritis

Drug Interactions

• Calcium supplements/antacids: Reduce absorption (administer ≥30 minutes apart) • NSAIDs: May increase GI irritation • PPIs: May reduce efficacy (controversial) • IV bisphosphonates: Additive skeletal effects • Aminoglycosides: Increased hypocalcemia risk

Warnings & Precautions

• Black Box Warning: Esophageal irritation/ulceration (proper administration crucial) • Risk of osteonecrosis of the jaw (especially with dental procedures) • Atypical femoral fractures with long-term use • Ensure adequate calcium/vitamin D intake • Monitor for hypocalcemia (correct before initiation)

Pregnancy & Lactation

Pregnancy: Category C (contraindicated) May cause fetal harm based on animal data Avoid use in women of childbearing potential not using contraception Lactation: Unknown if excreted in breast milk Generally contraindicated due to potential skeletal effects on infant

Monitoring Parameters

• Dual-energy X-ray absorptiometry (DXA) scans every 1-2 years • Serum calcium and phosphorus levels • Renal function tests (baseline and periodically) • Bone turnover markers (optional) • Dental evaluation before treatment in high-risk patients

Patient Counseling

• Take with 6-8 oz plain water first thing in morning • Remain upright for ≥30 minutes after dosing • Do not eat/drink anything (except water) for ≥30 minutes • Report new thigh/groin pain or jaw symptoms • Ensure adequate calcium/vitamin D intake • Do not lie down after administration

Storage & Stability

Store at 20-25°C (68-77°F) Keep in original container with desiccant Protect from moisture Do not use if tablets are discolored

Clinical Pearls

• 'Drug holidays' may be considered after 3-5 years in low-risk patients • Combine with weight-bearing exercise for optimal bone health • Consider switching to IV bisphosphonate if GI intolerance occurs • Assess vitamin D status before initiating therapy • Dental exams recommended before treatment in cancer patients

References

• Liberman UA, et al. N Engl J Med. 1995;333(22):1437-43 (FIT study) • Black DM, et al. J Clin Endocrinol Metab. 2000;85(11):4118-24 • Bone HG, et al. J Bone Miner Res. 2004;19(8):1241-9 • American Association of Clinical Endocrinologists (AACE) Guidelines 2020 • FDA Prescribing Information for Fosamax (2023)