Bisphosphonate

Alendronic acid

An oral bisphosphonate used to treat and prevent osteoporosis, including osteoporosis caused by glucocorticoids, and for Paget's disease.

Also called alendronate (US name).

Drug card

Class: Bisphosphonate
How it works: Binding bone mineral and blocking osteoclasts, so less bone is resorbed
Used for: Osteoporosis in women after menopause, and in men
Paget's disease of bone
Osteoporosis caused by glucocorticoids
Known for: Esophagitis, esophageal ulcers and erosions
Osteonecrosis of the jaw
Atypical femur fractures
Its name: -dronic acid, -dronate means a bisphosphonate

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Mechanism of action

How does alendronic acid work?

A second-generation bisphosphonate that settles in bone under osteoclasts and inhibits farnesyl pyrophosphate synthase. Under 1% of an oral dose is absorbed, and food, coffee or juice cut that further. Once buried in bone matrix it is inactive, yet its terminal half-life is over 10 years.

Like other bisphosphonates: Bisphosphonates are pyrophosphate analogs that bind tightly to hydroxyapatite and gather where osteoclasts are resorbing bone. Osteoclasts take them up as they work; alendronic and zoledronic acid then block farnesyl pyrophosphate synthase, so small GTPase signaling proteins go unprenylated and the cells stop resorbing or die. Bone turnover falls and bone density slowly rises.

Uses

What is alendronic acid used for?

Osteoporosis in women after menopause, and in men
Paget's disease of bone
Osteoporosis caused by glucocorticoids

Side effects

Side effects of alendronic acid

Esophagitis, esophageal ulcers and erosionsKnown forSerious
Osteonecrosis of the jawKnown forSerious
Atypical femur fracturesKnown forSerious
Indigestion, acid reflux and abdominal pain
Bone and muscle pain, sometimes severe
Joint pain and swelling
Swelling of the hands or legs (edema)
Low calcium (hypocalcemia)Serious
Stomach and duodenal ulcersSerious
Eye inflammation: uveitis, scleritisSerious
Flu-like aches and fever when starting
Severe skin reactions (SJS, TEN)Serious

Known for marks what an exam expects you to know it for.

Watch for

Cautions and what sets it apart

It is taken on waking with a full glass of plain water, then 30 minutes upright before any food, drink or other medicine.
Contraindicated with esophageal stricture or achalasia, inability to stay upright for 30 minutes, or low calcium.
Not recommended when creatinine clearance is below 35 mL/min.
Calcium, antacids and other multivalent cations block its absorption; aspirin and NSAIDs add to stomach irritation.

Good to know: Usually taken once a week. Because it stays in bone for years, the need to continue is reviewed after 3 to 5 years, and people at low fracture risk may stop or take a break.

Remember it

A way to remember it

BONES

B: Bone, joint and muscle pain, sometimes severe
O: Osteonecrosis of the jaw
N: Nephrotoxicity (kidney injury) with intravenous infusions
E: Esophagitis and ulcers from the tablets
S: Sit or stand upright for 30 minutes after a tablet taken with plain water

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Its name

-dronic acid, -dronate means bisphosphonate
INNs end in -dronic acid (alendronic acid); US names and salts end in -dronate (alendronate). Etidronic, ibandronic and risedronic acid share it.
Every drug name stem

Its class

Bisphosphonates

Other bisphosphonates with a card:

Zoledronic acid

Easily mixed up with selective estrogen receptor modulators.

All about bisphosphonates

Sources

Checked against

Written for biofideX in plain words, after checking these references:

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.

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Thyroid, steroids and bones

Alendronic acid is one of 9 drugs practiced together here: their classes, how they work, what they treat and what they're known for.

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