Alendronate (Fosamax, Merck) is a bisphosphonate drug used for osteoporosis and several other bone diseases. It is marketed alone as well as in combination with vitamin D (2,800 U and 5600 U, under the name Fosamax+D).
Pharmacokinetics
As with all potent bisphosphonates, the systemic bioavailability after oral dosing is low, averaging only 0.6 - 0.7 % in women and in men under fasting conditions. Intake together with meals and beverages other than water further reduces the bioavailability. The absorbed drug rapidly partitions, with approximately 50% binding to the exposed bone surface; the remainder is excreted unchanged by the kidneys. Unlike most drugs, the strong negative charge on the two phosphate moieties limits oral bioavailability, and in turn, the exposure to tissues other than bone is very low. After absorption in the bone, alendronate has an estimated terminal half-life of 10 years.
Uses
- Prophylaxis and treatment of female osteoporosis
- Treatment of male osteoporosis
- Prevention and treatment of corticosteroid-associated osteoporosis together with supplements of calcium and vitamin D
- Paget's disease
Dosage
Prophylaxis of osteoporosis in women: 5-10mg daily or 35-70mg weekly.
Therapy of osteoporosis in women and men : 10mg daily or 70mg weekly.
Osteoporosis under corticosteroids: 5-10mg daily or 35-70 mg weekly in men and premenopausal women or those receiving concomitant HRT. In postmenopausal women not receiving HRT the recommended dose is 10mg daily or 70mg weekly.
Paget's Disease: 40mg daily for 6 months.
The drug is to be taken only upon rising for the day with three swallows of water, not to exceed 6-8 oz. Stand, walk or sit and remain fasting for 30-45 minutes afterwards, then eat breakfast. Lying down or reclining prior to eating breakfast may cause gastroesophageal reflux and esophageal irritation. At least 30 minutes should be waited before meals or other beverages than water are taken in.
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