Bisphosphonates · Endocrine
Alendronate
alendronic acid · Fosamax®(brand names vary by market)
Sticks to bone, poisons the osteoclast, and demands a very specific half hour.
Mechanism
Binds hydroxyapatite and is taken up by osteoclasts, where it inhibits farnesyl pyrophosphate synthase and causes osteoclast apoptosis: less resorption, so formation wins.
Indications
- Osteoporosis in postmenopausal women and in men
- Glucocorticoid-induced osteoporosis
- Paget disease of bone
Formulations
Dosing concepts
Administration
Taken on waking, on an empty stomach, with a full glass of plain water, remaining upright and taking nothing else for at least 30 minutes. This is not fussiness: absorption is under 1 percent and the tablet causes oesophageal ulceration if it lingers.
Drug holiday
Because it persists in bone for years, therapy is usually reassessed after about five years, with a break considered in lower-risk patients.
Before starting
Correct vitamin D and calcium first; giving a potent antiresorptive to a vitamin D deficient patient can precipitate hypocalcemia.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- <1%, and effectively zero with food
- Half-life
- Terminal half-life in bone exceeds ten years
- Elimination
- renal: What is not taken up by bone is excreted unchanged; avoided at low creatinine clearance
- Protein binding
- ~78%
Adverse effects
- Oesophagitis and oesophageal ulcerationcommon & seriousAlmost entirely an administration-technique problem.
- Musculoskeletal paincommon
- HypocalcemiaseriousEspecially where vitamin D is deficient.
- Osteonecrosis of the jawseriousRare with oral osteoporosis doses; much more relevant at oncology doses.
- Atypical femoral fractureseriousRare; new thigh or groin pain on long-term therapy warrants imaging.
Contraindications & precautions
Contraindications
- Oesophageal stricture or achalasia
- Inability to sit or stand upright for 30 minutes
- Hypocalcemia
- Creatinine clearance below about 30 mL/min
Precautions
- Active upper gastrointestinal disease
- Planned dental extraction
- Vitamin D deficiency
Interactions
No curated interaction entries yet for this agent.
Monitoring
Calcium and vitamin D status before starting
Hypocalcemia is preventable and predictable
Renal function
It determines eligibility
New thigh or groin pain
The alarm for atypical femoral fracture
Dental review before starting where possible
Osteonecrosis risk is reduced by dealing with dental disease first
Counselling points
- First thing in the morning, on an empty stomach, with a full glass of plain water. Not coffee, not juice, not mineral water.
- Stay sitting or standing for at least 30 minutes afterwards, and do not eat or take other tablets during that time.
- Stop and contact us if you get heartburn, painful swallowing or chest pain on swallowing.
- Tell your dentist you take this before any extraction.
- Report any new pain in the thigh or groin.
Clinical pearls
- Almost every case of bisphosphonate oesophagitis traces back to the patient lying back down afterwards. Ten seconds of counselling prevents it.
- Its effect persists for years after stopping, which is what makes a drug holiday a coherent idea rather than an interruption of treatment.
References & review
- Alendronate product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.