Things worth knowing about "Bisphosphonate"
Bisphosphonates are medications that inhibit bone loss and are primarily used in the treatment of osteoporosis and bone metastases.
What Are Bisphosphonates?
Bisphosphonates (sometimes spelled biphosphonates) are a class of drugs that slow or inhibit the breakdown of bone tissue. They are among the most commonly prescribed medications for bone diseases and are used worldwide in clinical medicine. The name refers to their chemical structure: bisphosphonates contain two phosphonate groups attached to a central carbon atom.
Mechanism of Action
Bone is constantly being built up and broken down in the body. Specialized cells called osteoclasts are responsible for bone resorption. Bisphosphonates bind selectively to bone mineral and inhibit the activity of osteoclasts. This slows bone loss, helps maintain or even improve bone density, and reduces the risk of fractures.
Depending on their chemical structure, bisphosphonates are divided into two main groups:
- Nitrogen-containing bisphosphonates (e.g., alendronate, risedronate, zoledronate): These inhibit a key enzyme in osteoclast metabolism and are particularly potent.
- Non-nitrogen-containing bisphosphonates (e.g., etidronate, clodronate): These are converted into toxic metabolites within the cell, leading to osteoclast cell death.
Indications
Bisphosphonates are used in a variety of conditions where excessive bone resorption plays a role:
- Osteoporosis: The most common indication. Bisphosphonates significantly reduce the risk of fractures in people with low bone density.
- Bone metastases: In cancers that spread to the bone (e.g., breast or prostate cancer), bisphosphonates can slow bone destruction and relieve pain.
- Paget disease of bone: A condition where bone metabolism is severely disrupted.
- Multiple myeloma: A bone marrow cancer in which bisphosphonates are used as supportive therapy.
- Hypercalcemia: Elevated calcium levels in the blood, often caused by malignancy.
Dosage and Administration
Bisphosphonates are available in different formulations:
- Oral tablets: For example, alendronate taken once weekly. Important: The tablet must be taken with a full glass of water on an empty stomach, and the patient should remain upright for at least 30 minutes afterward to reduce the risk of esophageal irritation.
- Intravenous infusions: For example, zoledronate administered once yearly. This is particularly useful for patients who cannot tolerate oral formulations.
Side Effects
Like all medications, bisphosphonates can cause side effects:
- Gastrointestinal complaints: With oral use, heartburn, stomach pain, or esophageal irritation are common.
- Flu-like symptoms: Especially after the first infusion, fever, muscle aches, and fatigue may occur (known as an acute-phase reaction).
- Osteonecrosis of the jaw: A rare but serious complication in which bone tissue in the jaw dies. The risk is higher with high-dose intravenous use in cancer patients.
- Atypical femur fractures: With very long-term use (more than 5 years), there is a rare increased risk of unusual fractures of the thigh bone.
- Kidney impairment: Intravenous bisphosphonates can stress the kidneys and must be dose-adjusted or avoided in patients with renal insufficiency.
Contraindications and Precautions
Bisphosphonates should not be used in patients with:
- Severe renal insufficiency
- Low blood calcium levels (hypocalcemia)
- Pregnancy or breastfeeding
- Known hypersensitivity to the active substance
Before starting bisphosphonate therapy, a dental examination is recommended to minimize the risk of osteonecrosis of the jaw. Invasive dental procedures should be avoided during therapy where possible.
References
- Russell R.G.G. et al. - Bisphosphonates: The first 40 years. Bone, 2011;49(1):2-19.
- Black D.M. and Rosen C.J. - Clinical Practice: Postmenopausal Osteoporosis. New England Journal of Medicine, 2016;374(3):254-262.
- European Medicines Agency (EMA): Product information on bisphosphonates. Available at: https://www.ema.europa.eu