alendronate
Bisphosphonate· Brands: Fosamax, Fosavance, Binosto, AdronatPO
Mechanism of action
Alendronate is a bisphosphonate that inhibits osteoclast-mediated bone resorption. It binds to hydroxyapatite in bone, and when osteoclasts resorb bone, the drug is released, causing osteoclast inactivation and apoptosis. This reduces bone turnover and increases bone mineral density.
Pharmacokinetics
Alendronate is poorly absorbed orally and must be taken on an empty stomach with plain water. It has a very long half-life due to binding to bone. It is not metabolised and is excreted unchanged in the urine. Absorption is significantly reduced by food, beverages, or other medications.
Indications & dosing
Postmenopausal osteoporosis
Take on an empty stomach with a full glass of water; remain upright for at least 30 minutes.
- adult · PO: 70 mg once weekly · Take on an empty stomach with a full glass of water; remain upright for at least 30 minutes.
Osteoporosis in men
Take on an empty stomach with a full glass of water; remain upright for at least 30 minutes.
- adult · PO: 70 mg once weekly · Take on an empty stomach with a full glass of water; remain upright for at least 30 minutes.
Glucocorticoid-induced osteoporosis
Take on an empty stomach with a full glass of water; remain upright for at least 30 minutes. For patients receiving glucocorticoids, consider calcium and vitamin D supplementation.
- adult · PO: 70 mg once weekly · Take on an empty stomach with a full glass of water; remain upright for at least 30 minutes. For patients receiving glucocorticoids, consider calcium and vitamin D supplementation.
Paget's disease of bone
Take on an empty stomach with a full glass of water; remain upright for at least 30 minutes. Re-treatment may be considered after 6 months if necessary.
- adult · PO: 40 mg once daily · Take on an empty stomach with a full glass of water; remain upright for at least 30 minutes. Re-treatment may be considered after 6 months if necessary.
Contraindications & precautions
- Hypocalcaemia · Correct serum calcium levels before initiating therapy.
- Oesophageal abnormalities (e.g., stricture, achalasia) · Risk of severe oesophageal injury, including ulceration or perforation.
- Inability to sit or stand upright for at least 30 minutes · Needed to reduce oesophageal irritation and reflux.
- Severely impaired renal function (creatinine clearance <35 mL/min) · Not recommended due to risk of drug accumulation.
- Hypersensitivity to alendronate or any component · Cross-sensitivity to other bisphosphonates may occur.
- Pregnancy and breastfeeding · Limited data; use alternative therapy if possible.
- Administer alendronate with a full glass of water on an empty stomach, at least 30 minutes before the first food, drink, or medication of the day.
- Advise the patient to remain upright (sitting or standing) for at least 30 minutes after taking alendronate to reduce oesophageal irritation.
- Ensure adequate calcium and vitamin D intake, as alendronate may cause hypocalcaemia.
- Use caution in patients with swallowing difficulties or pre-existing gastrointestinal disorders (e.g., dyspepsia, acid reflux), as oesophageal irritation may be exacerbated.
- Monitor renal function before and during treatment; alendronate should not be used in patients with creatinine clearance <35 mL/min.
- Consider a dental examination before starting therapy, especially in patients at risk of osteonecrosis of the jaw (e.g., those with poor oral hygiene, cancer with chemotherapy, or long-term corticosteroid use).
Adverse effects
- Gastrointestinal irritation (e.g., dyspepsia, abdominal pain)
- Oesophageal irritation or ulcerationserious
- Musculoskeletal pain (bone, joint, muscle)
- Headache
- Osteonecrosis of the jawserious
- Atypical femoral fracturesserious
- Hypocalcaemiaserious
- Atrial fibrillationserious
- Hypersensitivity reactions (e.g., urticaria, angioedema)serious
Renal & hepatic adjustment
- eGFR 0–35: Contraindicated in severe renal impairment (CrCl < 35 mL/min) due to risk of accumulation and lack of clinical data. (avoid)
- eGFR 35–60: No dose adjustment required, but monitor renal function regularly.
Monitoring, pregnancy & toxicity
- Bone mineral density (BMD) · Annually or as clinically indicated
- Serum calcium · Baseline and periodically
- Serum vitamin D · Baseline and periodically
- Renal function (serum creatinine, eGFR) · Before starting and periodically thereafter
- Pregnancy: Alendronate is contraindicated in pregnancy. Animal studies show fetal harm, and the drug has a long half-life; women of childbearing age should use effective contraception and discontinue alendronate at least 6 months before attempting conception.
- Toxicity: Gastrointestinal irritation, including esophagitis, esophageal ulceration, and gastritis · Stop alendronate; advise the patient to remain upright for at least 30 minutes after taking the dose, and to discontinue if symptoms of esophageal irritation (e.g., dysphagia, odynophagia) occur. Use a proton pump inhibitor if needed.
- Toxicity: Hypocalcemia · Administer intravenous calcium gluconate or calcium chloride as appropriate; monitor serum calcium and magnesium; correct vitamin D deficiency.
- Toxicity: Osteonecrosis of the jaw (ONJ) · Discontinue alendronate; refer to oral surgeon; maintain good oral hygiene and avoid invasive dental procedures if possible.
- Toxicity: Atypical femoral fracture · Discontinue alendronate; assess bone health; consider bone imaging; manage fracture orthopedically.
Clinical notes
Alendronate is used for prevention and treatment of osteoporosis in postmenopausal women and men, and for glucocorticoid-induced osteoporosis. It is also used in Paget's disease of bone. Doses are typically taken once weekly or daily. It must be taken with a full glass of plain water on waking, and the patient must remain upright for at least 30 minutes to reduce oesophageal irritation. Common side effects include gastrointestinal upset, oesophageal ulceration, and musculoskeletal pain. Ensure adequate calcium and vitamin D intake. Contraindicated in renal impairment with low creatinine clearance. Monitor for signs of atypical femoral fractures and osteonecrosis of the jaw.
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BNF; local formulary