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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Vitamin D [EPC]
Alendronate is a potent bisphosphonate used to treat and prevent osteoporosis and Paget's disease. It works by altering the bone formation and breakdown cycle to increase bone mass and reduce fracture risk.
Name
Alendronate
Raw Name
ALENDRONATE SODIUM
Category
Vitamin D [EPC]
Salt Form
Sodium
Drug Count
6
Variant Count
39
Last Verified
February 17, 2026
RxCUI
904462, 904465, 904492, 904495, 904396, 904405, 904419, 904425, 904431, 1248077, 1248083, 904447, 904433
UNII
1C6V77QF41, 2UY4M2U3RA
About Alendronate
Alendronate is a potent bisphosphonate used to treat and prevent osteoporosis and Paget's disease. It works by altering the bone formation and breakdown cycle to increase bone mass and reduce fracture risk.
Detailed information about Alendronate
References used for this content
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Alendronate.
FDA approval for alendronate was first granted in 1995, marking a significant advancement in the management of metabolic bone diseases. Since its introduction, it has become a first-line therapy due to its proven efficacy in reducing the incidence of vertebral, hip, and wrist fractures. According to the National Osteoporosis Foundation (2024), alendronate remains a cornerstone of pharmacological intervention for individuals at high risk of fracture. It is important to note that while the prompt mentions Vitamin D [EPC], alendronate is pharmacologically classified as a bisphosphonate, though it is frequently co-administered or formulated with Vitamin D3 (Cholecalciferol) to ensure adequate calcium homeostasis during bone remodeling.
To understand how alendronate works, one must first understand the bone remodeling process. Bone is a living tissue that is constantly being broken down by cells called osteoclasts (resorption) and rebuilt by cells called osteoblasts (formation). In conditions like osteoporosis, the rate of resorption exceeds the rate of formation, leading to porous, fragile bones.
At the molecular level, alendronate works by binding strongly to hydroxyapatite (the mineral component of bone). When osteoclasts begin to resorb bone that contains alendronate, the drug is released and taken up by the osteoclast. Once inside the cell, alendronate inhibits an enzyme called farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This inhibition prevents the prenylation (attachment of lipid groups) of small GTP-binding proteins like Rho, Rac, and Rab, which are essential for the osteoclast's structural integrity and function. Without these proteins, the osteoclast's 'ruffled border' (the area that secretes acid to dissolve bone) disappears, and the cell eventually undergoes apoptosis (programmed cell death). By reducing the number and activity of osteoclasts, alendronate effectively slows the rate of bone loss, allowing osteoblasts to fill in the resorption cavities and increase overall bone mineral density (BMD).
Alendronate is FDA-approved for several specific indications:
Alendronate is available in several formulations to improve patient adherence:
> Important: Only your healthcare provider can determine if Alendronate is right for your specific condition. A thorough evaluation of your bone density (DEXA scan) and fracture risk (FRAX score) is typically required before starting therapy.
The dosage of alendronate depends strictly on the condition being treated and whether the goal is prevention or treatment.
Alendronate is not approved for use in pediatric patients. Clinical trials in children with osteogenesis imperfecta (brittle bone disease) did not demonstrate sufficient efficacy to warrant FDA approval, and concerns exist regarding the long-term impact of bisphosphonates on the growing skeleton.
No dosage adjustment is necessary for patients with mild-to-moderate renal impairment (Creatinine Clearance [CrCl] between 35 and 60 mL/min). However, alendronate is not recommended for patients with severe renal impairment (CrCl < 35 mL/min) due to a lack of clinical experience and the risk of drug accumulation.
Because alendronate is not metabolized by the liver and is excreted entirely by the kidneys, no dosage adjustments are required for patients with hepatic (liver) impairment.
In clinical trials, no overall differences in efficacy or safety were observed between patients over age 65 and younger patients. No age-based dose adjustment is required, though healthcare providers should always monitor renal function in older adults.
Proper administration is the most critical aspect of alendronate therapy. Failure to follow these steps can lead to severe esophageal irritation and prevent the drug from working.
If you are on a once-weekly schedule and miss a dose, take it the following morning after you remember. Do not take two tablets on the same day. Resume your regular schedule on your chosen day. If you are on a once-daily schedule, skip the missed dose and take the next dose at your regular time the following morning.
Signs of alendronate overdose may include hypocalcemia (low blood calcium), hypophosphatemia (low blood phosphorus), and upper gastrointestinal adverse events such as upset stomach, heartburn, esophagitis, or gastritis. In case of overdose, drink a full glass of milk and contact emergency services or a poison control center immediately. Do not induce vomiting, and do not lie down.
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or stop taking the medication without medical guidance, as bone density can begin to decline once the medication is discontinued.
Most patients tolerate alendronate well, but gastrointestinal issues are the most frequent complaints. Common side effects include:
> Warning: Stop taking Alendronate and call your doctor immediately if you experience any of these serious symptoms:
With prolonged use (typically beyond 3 to 5 years), the risk of atypical femur fractures and osteonecrosis of the jaw may increase. Because alendronate stays in the bone for many years, many healthcare providers now recommend a 'drug holiday' (a temporary period of discontinuation) for patients who have been on the drug for 5 years and are at low risk for fractures. This allows for normal bone remodeling to occur while the residual drug in the bone continues to provide protection.
No FDA black box warnings currently exist for alendronate. However, the FDA has issued several 'Safety Communications' regarding the risks of atypical subtrochanteric femur fractures and the potential for severe musculoskeletal pain. The labels for all bisphosphonates were updated in 2011 to include these warnings. Patients are advised to report any new hip or thigh pain to their physician immediately.
Report any unusual symptoms to your healthcare provider, especially those involving the digestive tract or unusual bone pain.
Alendronate is a powerful medication that requires strict adherence to safety protocols. The most critical safety concern involves the upper gastrointestinal (GI) tract. Because alendronate can cause severe irritation, it must be taken exactly as prescribed to avoid esophageal damage. Patients with a history of Barrett's esophagus or swallowing disorders must use extreme caution.
There are no FDA black box warnings for Alendronate. However, the medication carries significant 'Warnings and Precautions' that are treated with high clinical importance by prescribing physicians.
Alendronate generally does not affect the ability to drive or operate machinery. However, rare side effects like dizziness or blurred vision have been reported. Patients should observe their reaction to the medication before engaging in these activities.
While there is no direct chemical interaction between alcohol and alendronate, excessive alcohol consumption is a significant risk factor for osteoporosis and can increase the risk of stomach irritation. It is generally advised to limit alcohol intake while on this medication.
Unlike many medications, alendronate does not need to be tapered. However, its effects persist for years after stopping. The decision to discontinue (a 'drug holiday') should be made by a doctor based on a risk-benefit analysis of the patient's fracture risk.
> Important: Discuss all your medical conditions, especially any history of heartburn or kidney disease, with your healthcare provider before starting Alendronate.
There are no drugs that are strictly contraindicated for simultaneous use in the traditional sense, but calcium supplements, antacids, and oral medications containing multivalent cations (like magnesium or aluminum) must not be taken within 30 minutes of alendronate. If taken together, these substances will bind to alendronate in the stomach and prevent any of the drug from being absorbed, rendering the treatment useless.
Alendronate may interfere with bone-imaging agents. In bone scans, bisphosphonates can cause increased uptake at sites of high bone turnover, which is the intended effect but must be interpreted correctly by the radiologist. It may also cause mild, transient decreases in serum calcium and phosphate levels in blood tests.
Mechanism of Interactions: Most interactions with alendronate are pharmacokinetic (interference with absorption) rather than pharmacodynamic (interference with the drug's action). Because alendronate is not metabolized by the liver, it lacks the complex CYP450 interactions common with other medications.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, including over-the-counter pain relievers.
Alendronate must NEVER be used in the following circumstances:
These conditions require a careful risk-benefit analysis by a healthcare provider:
While rare, patients who have had a severe allergic reaction to other bisphosphonates (such as risedronate, ibandronate, or zoledronic acid) may also react to alendronate. This is known as cross-sensitivity within the bisphosphonate class.
> Important: Your healthcare provider will evaluate your complete medical history, including your ability to follow the strict administration instructions, before prescribing Alendronate.
Alendronate is classified as Pregnancy Category C. There are no adequate and well-controlled studies in pregnant women. Animal studies have shown that bisphosphonates are incorporated into the maternal bone matrix and gradually released over years. There is a theoretical risk that this could cause fetal harm (specifically skeletal abnormalities or low calcium) if a woman becomes pregnant even years after stopping the drug. Alendronate should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus.
It is not known whether alendronate is excreted in human milk. Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants, a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
Alendronate is not indicated for use in children. Safety and effectiveness have not been established in pediatric populations. In trials for osteogenesis imperfecta, no significant reduction in fracture risk was found, and there are concerns about the drug's long-term retention in a growing skeleton.
In clinical trials, over 40% of patients were 65 years of age or older. No overall differences in safety or effectiveness were observed between these patients and younger patients. However, older adults are more likely to have decreased renal function and may be taking other medications (polypharmacy) that increase the risk of GI irritation. Fall risk assessment is crucial in this population, as alendronate treats the bone density but does not prevent the falls that lead to fractures.
For patients with mild to moderate renal impairment (CrCl 35 to 60 mL/min), no dose adjustment is necessary. For those with severe renal impairment (CrCl < 35 mL/min), alendronate is not recommended. The drug is cleared by the kidneys, and impaired clearance could lead to excessively high levels of the drug in the bone over time.
No dosage adjustment is necessary for patients with hepatic impairment. Alendronate is not metabolized by the liver, so liver disease does not affect the drug's concentration or safety profile.
> Important: Special populations, particularly pregnant women and those with kidney disease, require individualized medical assessment and close monitoring by a specialist.
Alendronate is a nitrogen-containing bisphosphonate that acts as a potent inhibitor of osteoclast-mediated bone resorption. It has a high affinity for hydroxyapatite crystals in the bone matrix. Once internalized by osteoclasts via endocytosis during the resorption process, alendronate inhibits the enzyme farnesyl pyrophosphate (FPP) synthase. This enzyme is a key component of the mevalonate pathway, which is responsible for producing cholesterol and isoprenoid lipids. The inhibition of FPP synthase prevents the prenylation of small GTPase proteins (such as Rho and Rab), which are essential for the formation of the osteoclast's ruffled border and its ability to secrete acid. This leads to osteoclast inactivation and apoptosis, thereby reducing bone turnover.
Alendronate leads to a significant increase in Bone Mineral Density (BMD) and a decrease in biochemical markers of bone resorption (such as urinary N-telopeptide). The onset of effect on bone resorption markers is seen within one month, reaching a plateau within 3 to 6 months. The effects on BMD are progressive over several years of treatment.
| Parameter | Value |
|---|---|
| Bioavailability | 0.6% - 0.7% (Fasting) |
| Protein Binding | ~78% |
| Half-life | >10 years (Terminal half-life in bone) |
| Tmax | 1 - 2 hours |
| Metabolism | None |
| Excretion | Renal (100% of absorbed dose) |
Alendronate is classified as a Bisphosphonate. It is part of the second generation of bisphosphonates (aminobisphosphonates), which are significantly more potent than first-generation agents like etidronate. Related medications include Risedronate (Actonel), Ibandronate (Boniva), and Zoledronic Acid (Reclast).
Medications containing this ingredient
Common questions about Alendronate
Alendronate is primarily used to treat and prevent osteoporosis, a condition where bones become thin, weak, and easily broken. It is most commonly prescribed for postmenopausal women but is also used to increase bone mass in men with osteoporosis. Additionally, it is used to treat bone loss caused by long-term use of steroid medications (glucocorticoid-induced osteoporosis). Healthcare providers also prescribe it for Paget's disease of bone, a condition that causes bones to grow too large and weak. By slowing down the rate at which bone is broken down, alendronate helps to maintain or increase bone density and significantly reduces the risk of fractures.
The most common side effects of alendronate are gastrointestinal in nature, including stomach pain, heartburn, and acid reflux. Some patients may also experience nausea, constipation, or diarrhea during the first few weeks of treatment. Musculoskeletal pain, which can manifest as aching in the joints or muscles, is also frequently reported. Most of these side effects are mild, but it is important to follow the administration instructions carefully to minimize stomach irritation. If you experience severe chest pain or difficulty swallowing, you should contact your doctor immediately, as these could be signs of esophageal irritation.
There is no known direct chemical interaction between alendronate and alcohol; however, caution is advised. Excessive alcohol consumption is a known risk factor for developing osteoporosis because it can interfere with the body's ability to absorb calcium and produce new bone. Furthermore, both alcohol and alendronate can irritate the lining of the stomach and esophagus, potentially increasing the risk of gastritis or ulcers. Most healthcare providers recommend limiting alcohol intake to support bone health and reduce the chance of gastrointestinal side effects. Always discuss your lifestyle habits with your doctor when starting a new medication.
Alendronate is generally not recommended during pregnancy unless the potential benefits clearly outweigh the risks. It is classified as Pregnancy Category C, meaning animal studies have shown potential harm, but there are no adequate human studies. A significant concern is that alendronate stays in the human skeleton for many years, and its release during pregnancy could theoretically affect the developing baby's bone growth or calcium levels. Women who are pregnant or planning to become pregnant should discuss alternative treatments with their physician. If you discover you are pregnant while taking alendronate, notify your healthcare provider immediately.
Alendronate begins working at the cellular level within days of the first dose, but its effects on bone density are not immediate. Changes in biochemical markers of bone turnover can usually be detected in blood or urine tests within 3 to 6 months. However, it typically takes at least 12 to 24 months of consistent use to see a measurable increase in bone mineral density on a DEXA scan. The primary goal of the medication is the long-term reduction of fracture risk, which has been proven in clinical trials lasting three years or more. Patience and strict adherence to the dosing schedule are key to the success of the treatment.
You can stop taking alendronate without experiencing immediate withdrawal symptoms, but you should never do so without consulting your doctor. Because the drug binds to your bone mineral, its protective effects will persist for a significant period even after you stop taking it. However, once the medication is discontinued, your bone density may eventually begin to decline again at the same rate as before you started treatment. Your doctor may suggest a 'drug holiday' after 3 to 5 years of use if your fracture risk is low. This decision is based on a complex assessment of your bone health and fracture history.
If you miss a dose of alendronate, the protocol depends on your specific dosing schedule. For those taking the once-weekly 70 mg dose, take the missed dose on the morning after you remember and then return to your regular weekly schedule on your original day. Never take two weekly doses on the same day. If you are taking the once-daily 10 mg dose, simply skip the missed dose and take your next dose at the usual time the following morning. Do not try to 'double up' to make up for a missed dose, as this significantly increases the risk of severe stomach and esophageal irritation.
Weight gain is not a recognized or common side effect of alendronate according to clinical trial data and FDA labeling. Most patients do not experience any significant changes in body weight while taking this medication. If you notice rapid weight gain or swelling (edema) in your legs or hands, it may be due to a different underlying condition or a different medication. It is always a good idea to monitor your weight and report any sudden or unexplained changes to your healthcare provider. Maintaining a healthy weight is actually beneficial for bone health, as being underweight is a risk factor for osteoporosis.
Alendronate can be taken with many other medications, but timing is critical to avoid interactions. You must wait at least 30 minutes after taking alendronate before taking any other oral medications, including vitamins, calcium, or antacids. This is because other drugs can bind to alendronate in the stomach and prevent it from being absorbed into your bloodstream. Special caution is needed if you take NSAIDs like ibuprofen or aspirin, as these can increase the risk of stomach ulcers when combined with alendronate. Always provide your doctor with a full list of your current medications to ensure there are no dangerous interactions.
Yes, alendronate sodium is widely available as a generic medication in both daily and weekly tablet forms. The generic versions are required by the FDA to have the same active ingredient, strength, dosage form, and route of administration as the brand-name drug, Fosamax. Generic alendronate is typically much more affordable than the brand-name version and is covered by most insurance plans. There is also a generic oral solution available for patients who have difficulty swallowing tablets. Switching to a generic version is a common and safe practice that should be discussed with your pharmacist or healthcare provider.