The bisphosphonates are pyrophosphate analogues that become incorporated into bone matrix and suppress osteoclastic activity, thereby reducing bone turnover and increasing bone mass, which makes them valuable agents for the prevention and therapy of osteoporosis.
Liver safety of Bisphosphonates
Therapy with the bisphosphonates has been associated with a low rate of serum enzyme elevations during therapy and has been linked to rare instances of clinically apparent liver injury.
Mechanism of action of Bisphosphonates
Bisphosphonates are pyrophosphate analogues that have two phosphonate groups attached to a central carbon atom that replaces the oxygen present in pyrophosphate. The bisphosphonates bind calcium and are rapidly taken up in bone matrix where they suppress osteoclastic activity and change the balance between bone resorption and bone formation, thus increasing bone mass. The bisphosphonates have been shown to be effective in treating malignant hypercalcemia and in preventing and treating osteoporosis. Six bisphosphonates have been approved for use in the United States (pronunciation and year of approval given in parentheses) and they differ in formulation, recommended dose regimen, spectrum of activity and clinical indications.
• Alendronate (a len' droe nate) (1995) is available in tablets of 5 and 10 mg for daily use, 35, 40 and 70 mg (with and without vitamin D) for weekly use, and as a suspension for oral use in several generic forms and under the brand name Fosamax. Indications include prevention and treatment of osteoporosis and treatment of Paget disease of bone.
• Etidronate (e" ti droe' nate) (1977) is available in tablets of 200 and 400 mg for daily use in generic forms and under the trade name Didronel. Indications include Paget disease of bone and heterotopic ossification, but it has also been used off label for therapy of osteoporosis.
• Ibandronate (eye" ban droe' nate) (2003) is available in tablets of 2.5 mg for daily and 150 mg for monthly use and as an intravenous formulation under the trade name Boniva. Indications include prevention and treatment of osteoporosis.
• Pamidronate (pam" i droe' nate) (1991) is available as an intravenous formulation generically and under the trade name Aredia. Indications include hypercalcemia of malignancy, multiple myeloma and Paget disease of bone.
• Risedronate (ris" e droe' nate) (1998) is available in tablets of 5 mg for daily use, 30 and 35 mg for weekly use, and 75 and 150 mg for monthly use in generic forms and under the trade name Actonel. Indications include osteoporosis and Paget disease of bone.
• Zoledronic acid (zoe" le droe' nate) (2001) is available as several intravenous formulations generically and under the brand names Zometa and Reclast. Indications and dosage vary by preparation, but include prevention and treatment of osteoporosis, Paget disease of bone, hypercalcemia of malignancy and multiple myeloma.
Side effects of Bisphosphonates
The side effects of the bisphosphonates vary by route of administration, but are largely class specific. The oral formulations are generally well tolerated, but are recommended to be given on an empty stomach and with care that they enter the stomach (by drinking water and remaining upright) to avoid esophageal irritation and potential ulceration. Common side effects of oral formulations include headache, abdominal discomfort, dyspepsia, nausea and hypocalcemia. The intravenous formulations of the bisphosphonates can be associated with local infusion reactions and in an acute phase reaction in up to 30% of patients. This is characterized by a flu-like syndrome primarily with the initial infusion. Symptoms arise within 10 to 20 hours after the infusion and are accompanied by increases in C reactive protein, decreases in serum zinc and, in some instances, minor elevations in serum enzymes several days later. Severe side effects of the bisphosphanates are rare, but have included esophageal ulcer, gastrointestinal bleeding, atrial fibrillation and, with long-term treatment, osteonecrosis of the jaw and atypical femoral fractures.