Overview
Alendronate is a bisphosphonate medication widely used to prevent and treat osteoporosis, particularly in postmenopausal women and older men. It works by slowing down bone loss, increasing bone density, and reducing the risk of bone fractures, including hip and spine fractures.

Mechanism of Action
It binds to hydroxyapatite crystals in bone and acts as a specific inhibitor of osteoclast-mediated bone resorption. Osteoclasts are cells that break down bone tissue. By inhibiting their activity, alendronate decreases the rate of bone turnover, allowing bone formation by osteoblasts to outpace resorption, leading to a net gain in bone mass.

Dosage and Administration
For the treatment of osteoporosis, the usual dose is 70 mg taken once weekly. It must be taken exactly as directed: first thing in the morning on an empty stomach, with a full glass of plain water, at least 30 minutes before any food, beverage, or other medication. Patients must remain fully upright (sitting or standing) for at least 30 minutes after taking it to prevent esophageal irritation.

Side Effects
Common side effects include gastrointestinal discomfort, such as abdominal pain, acid reflux, and nausea. A significant risk is esophageal irritation or ulceration if not taken correctly. Rare but serious side effects include osteonecrosis of the jaw (ONJ) and atypical femoral fractures with long-term use.

Contraindications
It is contraindicated in patients with abnormalities of the esophagus that delay esophageal emptying, such as stricture or achalasia, and in patients unable to stand or sit upright for at least 30 minutes. It is also contraindicated in patients with hypocalcemia.

Pregnancy and Lactation
It is not indicated for use in pregnant women. Bisphosphonates are incorporated into the bone matrix and gradually released over years. It is not known if it is excreted in human milk.