Alendronic Acid
Is It Right for You?
A complete guide to Alendronic Acid — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Alendronic Acid?
Alendronic acid (also known as alendronate) is a nitrogen-containing bisphosphonate — the most widely prescribed class of medication for the prevention and treatment of osteoporosis. It works by inhibiting osteoclast-mediated bone resorption, thereby slowing bone loss, increasing bone mineral density (BMD), and significantly reducing the risk of vertebral and non-vertebral fractures, including hip fractures.
Alendronic acid is available as oral tablets of 10 mg (for daily dosing) and 70 mg (for weekly dosing). The 70 mg once-weekly tablet is the most commonly prescribed formulation in the UK due to its equivalent efficacy and substantially improved tolerability and convenience compared to daily dosing. An effervescent 70 mg weekly tablet is also available for patients who have difficulty swallowing standard tablets.
Bisphosphonates have a remarkable affinity for hydroxyapatite in bone matrix, where they accumulate over time. This results in a prolonged pharmacological effect that persists for months to years after the medication is discontinued — a relevant consideration in both long-term treatment planning and the management of rare but serious side effects.
Alendronic acid is a prescription-only medication in the UK. A licensed clinician must assess your bone density, fracture risk, renal function, and medical history — including dental health — before prescribing.
What Conditions Is Alendronic Acid Used For?
Alendronic Acid is Used For:
treatment and prevention of osteoporosis in postmenopausal women; reduces risk of vertebral fractures by approximately 50% and hip fractures by approximately 40% over three years
prevention and treatment of bone loss in patients on long-term corticosteroid therapy (prednisolone ≥5 mg/day or equivalent)
treatment of osteoporosis in men at increased fracture risk
although other bisphosphonates are more commonly used, alendronic acid is occasionally used for this indication
Alendronic acid improves bone mineral density and significantly reduces fracture risk, but it does not fully reverse established osteoporosis or restore the microarchitectural integrity of bone that has been lost. Calcium and vitamin D supplementation, weight-bearing exercise, fall prevention strategies, and addressing modifiable risk factors remain essential components of osteoporosis management.
How Does Alendronic Acid Work?
Bone is a dynamic tissue in a constant state of remodelling, involving coordinated cycles of resorption by osteoclasts and formation by osteoblasts. In osteoporosis, this balance is disrupted — resorption outpaces formation, resulting in progressive loss of bone mass and microarchitectural deterioration.
Bisphosphonate incorporation into bone — after oral absorption, alendronic acid is rapidly deposited onto the surface of bone mineral (hydroxyapatite), particularly at sites of active remodelling. When osteoclasts resorb this bone, they internalise the bisphosphonate.
Osteoclast inhibition — within the osteoclast, alendronic acid inhibits farnesyl pyrophosphate synthase, a key enzyme in the mevalonate pathway. This disrupts the prenylation of signalling proteins essential for osteoclast cytoskeletal function and survival, leading to osteoclast apoptosis and a reduction in bone resorption.
Net skeletal effect — by suppressing osteoclast activity, alendronic acid shifts the remodelling balance in favour of bone formation, resulting in measurable increases in BMD at the lumbar spine, hip, and femoral neck over time. Fracture risk reduction is detectable within the first year of treatment and increases progressively over three to five years.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Take alendronic acid first thing in the morning, on an empty stomach, at least 30 minutes before eating, drinking (other than plain water), or taking any other medication. This is critical — food, drink, and other medications dramatically reduce absorption.
Swallow the tablet whole with a full glass of plain water (at least 200 mL). Do not use mineral water, juice, tea, or coffee.
Remain upright (sitting, standing, or walking) for at least 30 minutes after taking the tablet and until after eating your first meal of the day. Do not lie down. This is essential to reduce the risk of oesophageal irritation and ulceration.
Do not chew or suck the tablet — this increases the risk of oropharyngeal ulceration.
Calcium and vitamin D supplementation should be co-prescribed unless dietary intake is demonstrably adequate. Calcium supplements must not be taken within 30 minutes of alendronic acid as they inhibit absorption.
Treatment duration should typically be reviewed at three to five years. A drug holiday may be appropriate in lower-risk patients, given the prolonged skeletal retention of bisphosphonates.
Side Effects of Alendronic Acid
Most side effects are mild and resolve on their own. Serious side effects are rare but require immediate medical attention.
- Oesophageal irritation, dysphagia, or heartburn — particularly if administration instructions are not followed correctly
- Abdominal pain or discomfort
- Nausea or constipation
- Headache
- Musculoskeletal pain (bone, joint, or muscle pain) — may be severe; usually reversible on discontinuation
- Mild and transient flu-like symptoms (more commonly with intravenous bisphosphonates but occasionally with oral forms)
- Oesophageal ulceration or perforation — severe chest pain, pain on swallowing, new or worsening heartburn; seek urgent medical review
- Osteonecrosis of the jaw (ONJ) — rare; exposed necrotic bone in the oral cavity, jaw pain, loose teeth, poor wound healing after dental procedures; risk is low with oral bisphosphonates but real, particularly in patients with poor dental health or on concurrent immunosuppressants
- Atypical femoral fracture — rare; stress fracture of the femoral shaft after minimal or no trauma; may present with thigh or groin prodromal pain; associated with prolonged bisphosphonate use (typically >5 years)
- Severe hypocalcaemia — particularly in patients with vitamin D deficiency or hypoparathyroidism; tetany, muscle cramps, perioral numbness
- Severe musculoskeletal pain — rarely incapacitating; usually resolves on discontinuation
- Uveitis or scleritis — rare ocular inflammation; seek ophthalmological review
Oesophageal adverse effects — including irritation, ulceration, and, rarely, stricture — are the most common reason patients discontinue alendronic acid. The overwhelming majority of these events are preventable by strict adherence to administration instructions: taking the tablet on an empty stomach with a full glass of water and remaining upright for 30 minutes.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting Alendronic Acid.
These significantly impair absorption of alendronic acid by chelating the bisphosphonate in the gastrointestinal lumen. They must not be taken within 30 minutes (ideally two hours) of alendronic acid.
Concurrent use increases the risk of upper gastrointestinal adverse events, including oesophageal, gastric, and duodenal ulceration. Use with caution; GI protective therapy should be considered.
Similar to NSAIDs — concurrent use increases upper GI risk. Monitor for symptoms of GI irritation.
Concurrent use may cause additive hypocalcaemia due to increased renal calcium excretion; monitor calcium levels.
Long-term glucocorticoid use is itself a major risk factor for osteoporosis and compounds the indication for bisphosphonate therapy; alendronic acid should be co-prescribed in patients commencing long-term corticosteroids.
These may reduce alendronic acid absorption; take at a different time of day.
Important Warnings
Alendronic acid is contraindicated in patients with oesophageal abnormalities that delay oesophageal emptying — including stricture, achalasia, or severe dysmotility — and in patients who are unable to sit or stand upright for at least 30 minutes. Patients with Barrett's oesophagus require specialist review before initiating therapy.
Alendronic acid is contraindicated in patients with severe renal impairment (eGFR <35 mL/min). Bisphosphonates are renally excreted and accumulate in renal failure, increasing the risk of hypocalcaemia and renal toxicity. Renal function should be assessed before initiating treatment and monitored periodically.
Patients should maintain good oral hygiene and attend regular dental check-ups before and during treatment. Invasive dental procedures (extractions, implants) carry a higher risk of ONJ in bisphosphonate-treated patients. The treating dentist should be informed of bisphosphonate use prior to any dental surgery. Risk is substantially lower with oral alendronic acid than with intravenous bisphosphonates used in oncology.
Patients on long-term alendronic acid (typically more than five years) should be made aware of the rare risk of atypical femoral fracture. New thigh or groin pain during treatment should be investigated promptly. A treatment review and possible drug holiday should be discussed at the five-year mark.
Pre-existing hypocalcaemia must be corrected before commencing alendronic acid. Adequate calcium and vitamin D intake must be ensured throughout treatment to prevent bisphosphonate-induced worsening of hypocalcaemia.
Alendronic acid is not indicated in premenopausal women outside specific clinical circumstances. It should be avoided in pregnancy and breastfeeding. Given its prolonged skeletal retention, women of childbearing potential should be counselled about this prior to commencing treatment.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Alendronic Acid FAQs
Alendronic acid is highly irritant to the oesophagus. Remaining upright ensures the tablet passes quickly into the stomach and is not in prolonged contact with the oesophageal lining, reducing the risk of ulceration and irritation.
Most guidelines recommend a review at three to five years of treatment. Patients at higher fracture risk may continue beyond five years, while those at lower risk may be offered a drug holiday — a period of planned discontinuation — because the skeletal retention of bisphosphonates provides ongoing protection for some time after stopping.
In most cases, yes. Adequate calcium and vitamin D are essential for alendronic acid to work effectively and to prevent hypocalcaemia. Your clinician will assess your dietary intake and prescribe supplements if needed.
For routine dental care (check-ups, fillings, hygienist), no specific precautions are needed. For invasive procedures such as tooth extractions or implants, inform your dentist that you are taking alendronic acid, as there is a small risk of osteonecrosis of the jaw associated with bisphosphonate use and dental surgery.
Yes — alendronic acid is licensed for the treatment of osteoporosis in men at increased fracture risk, and is an effective option regardless of gender.
If you are taking the weekly 70 mg tablet and miss a dose, take it the morning after you remember. Do not take two tablets on the same day. Then return to your usual once-weekly schedule.