[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Bisphosphonates](https://durgical.com/en/pharmacology/classes/bisphosphonates/) › Alendronic acid (alendronate)

# Alendronic acid (alendronate)

## Bisphosphonates?

Bisphosphonates

## Pregnancy: avoid?

Not used in pregnancy; it stays in bone for years, so a possible effect on the fetal skeleton is a concern even after it is stopped.

An oral bisphosphonate that slows bone loss and lowers fracture risk in osteoporosis. It must be taken in a strict way to protect the oesophagus.

Updated Nov 1, 2026

Also called: Alendronate sodium

## Quick facts

**Group**
[Bisphosphonates](https://durgical.com/en/pharmacology/classes/bisphosphonates/)

**Target**
Farnesyl pyrophosphate synthase (FPPS), an enzyme of the mevalonate pathway in osteoclasts

**Used for**
Treatment and prevention · Osteoporosis in men

**Key effects**
Abdominal pain · Constipation · Musculoskeletal pain

**Monitor**
Serum calcium · Kidney function · New heartburn

**ATC**
M05BA04

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Clinical What the labels mean

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

✂**Farnesyl pyrophosphate synthase (FPPS), an enzyme of the mevalonate pathway in osteoclasts**Alendronic acid (alendronate)

ⓘ The figure shows alendronate itself in the active site of human farnesyl pyrophosphate synthase.

**Target in 3D:** Farnesyl pyrophosphate synthase (FPPS), an enzyme of the mevalonate pathway in osteoclasts. PDB structure 2F92 (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/2F92) · Drag to rotate · pinch to zoom

Alendronate is a nitrogen-containing bisphosphonate. It binds the hydroxyapatite of bone at sites of resorption and is taken up by osteoclasts, where it inhibits farnesyl pyrophosphate synthase. Osteoclasts lose activity and die, resorption falls and bone formation gradually exceeds it, so bone density rises and vertebral and hip fractures become less frequent. It does not stop osteoclasts from being recruited, and it stays in the skeleton for years.

- Alendronate binds the bone mineral where bone is being resorbed
- Osteoclasts take it up as they dissolve the bone
- It blocks farnesyl pyrophosphate synthase and the osteoclast stops working
- Resorption falls, bone density rises and fractures drop

## Indications

- Treatment and prevention of postmenopausal osteoporosis [Osteoporosis →](https://durgical.com/en/conditions/osteoporosis/)
- Reduction of vertebral fractures in osteoporosis [Osteoporotic vertebral compression fracture →](https://durgical.com/en/conditions/osteoporotic-vertebral-compression-fracture/)
- Osteoporosis in men and glucocorticoid-induced osteoporosis
- Paget disease of bone [Paget disease of bone →](https://durgical.com/en/conditions/paget-disease-of-bone/)

## Adverse effects

### Common

- Abdominal pain, nausea, dyspepsia
- Constipation, diarrhoea, bloating
- Musculoskeletal pain
- Headache
- Taste changes

### Serious (rare, important)

- Oesophagitis, oesophageal ulcer, stricture or bleeding
- Osteonecrosis of the jaw
- Atypical femoral shaft fracture (dull thigh or groin pain beforehand)
- Severe bone, joint or muscle pain
- Hypocalcaemia if it was not corrected beforehand

## Contraindications

- Oesophageal abnormalities that delay emptying, such as stricture or achalasia
- Inability to stand or sit upright for at least 30 minutes
- Hypocalcaemia
- Hypersensitivity to the product
- Not recommended with severe kidney impairment

## Key interactions

**Calcium supplements, antacids and other products with calcium, magnesium, iron or aluminium**
They bind alendronate in the gut and block its absorption; other oral medicines wait at least 30 minutes

**Aspirin and other NSAIDs**
More upper gastrointestinal irritation

**Coffee, juice, milk and mineral water**
Much less absorption; only plain water is used

## What is monitored

- Serum calcium and vitamin D before starting
- Kidney function
- Bone density and fracture risk over time (need to continue after several years)
- New heartburn, pain on swallowing or chest pain
- Dental health; thigh or groin pain

## Administration and safety

- Taken first thing in the morning, after getting up, on an empty stomach, with a full glass of plain water
- The tablet is swallowed whole; the person stays sitting or standing for at least 30 minutes and does not lie down
- Food, drinks and other medicines, vitamins or antacids wait at least 30 minutes
- Weekly forms are taken on the same day each week

## Pregnancy and breastfeeding

Not used in pregnancy; it stays in bone for years, so a possible effect on the fetal skeleton is a concern even after it is stopped.

## Nursing care

- Check that the person can stay upright before giving it; if not, it is not given
- Teach the full ritual: on waking, empty stomach, plain water, upright, nothing else for 30 minutes
- Ask about heartburn, pain on swallowing or chest pain and report them; the drug may need to stop
- Check calcium and vitamin D intake and dental health; ask about planned dental extractions
- Report new thigh, hip or groin pain

## Pharmacokinetics

**Absorption**
Very poorly absorbed by mouth; food, coffee, juice and minerals cut absorption almost to nothing

**Distribution**
Binds bone quickly; the rest is not taken up by tissues

**Metabolism**
Not metabolised

**Elimination**
The part not stored in bone leaves unchanged in the urine

**Half-life**
Its terminal half-life in the skeleton is estimated at more than 10 years

## Memory aid

Alendronate's morning rule = «WAKE UP STRAIGHT»: on Waking, Alone (no food), plain water, Keep upright, wait before Eating.

## Test yourself

Think of the answer, then tap the question to see it.

## Which instructions protect the oesophagus and absorption with alendronate?

First thing in the morning on an empty stomach, with plain water, staying upright at least 30 minutes and waiting before food, drink or other medicines.

## Why is alendronate not given with calcium or antacids at the same time?

Calcium and other polyvalent cations bind it in the gut and prevent its absorption, which is already very low.

## Can you name two conditions in which alendronate is contraindicated?

Any two of: oesophageal strictures or achalasia, inability to stay upright for 30 minutes, hypocalcaemia, hypersensitivity.

## Which rare adverse effect is linked to dental extractions during bisphosphonate treatment?

Osteonecrosis of the jaw: exposed bone that does not heal, usually after an extraction or local infection.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/alendronic-acid/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## What the labels mean

**Pregnancy: avoid**
Not used in pregnancy; it stays in bone for years, so a possible effect on the fetal skeleton is a concern even after it is stopped.

## Connections

## Related drugs 4

- [Risedronic acid (risedronate)](https://durgical.com/en/pharmacology/risedronic-acid/)
- [Zoledronic acid](https://durgical.com/en/pharmacology/zoledronic-acid/)
- [Denosumab](https://durgical.com/en/pharmacology/denosumab/)
- [Raloxifene](https://durgical.com/en/pharmacology/raloxifene/)

## Related conditions 3

- [Osteoporosis](https://durgical.com/en/conditions/osteoporosis/)
- [Osteoporotic vertebral compression fracture](https://durgical.com/en/conditions/osteoporotic-vertebral-compression-fracture/)
- [Paget disease of bone](https://durgical.com/en/conditions/paget-disease-of-bone/)

[← Back to the class: Bisphosphonates](https://durgical.com/en/pharmacology/classes/bisphosphonates/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Alendronate: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a601011.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [DailyMed - ALENDRONATE SODIUM tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=815a87c4-e489-4eb9-9a2e-fb7a16642f01) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=M05BA04) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/alendronic-acid/