Medical Sciences Bulletin Contents
Reprinted from the August 1995 issue of Medical Sciences Bulletin , published by Pharmaceutical Information Associates, Ltd.
See also...
Indication: Osteoporosis
Drug Tradename: FosamaxManufacturer: MerckOther drugs mentioned:
Osteoporosis occurs when bone resorption outpaces bone formation. Bone is constantly undergoing cycles of resorption and formation (remodeling) to maintain the concentration of calcium and phosphate in the extracellular fluid. When serum calcium concentration drops below a certain level, parathyroid hormone secretion increases, and this hormone stimulates bone resorption by osteoclasts to restore calcium levels to normal. Low calcium also slows renal calcium excretion and acts via vitamin D3 to increase intestinal calcium absorption. With aging, vitamin D3 levels drop, resulting in calcium malabsorption that, in turn, stimulates bone resorption. Estrogen deficiency exacerbates this problem by increasing the sensitivity of bone to resorbing agents.
The primary strategy for preventing osteoporosis has been estrogen therapy, although women who take estrogen usually do so for relief of postmenopausal symptoms (e.g., hot flashes); the effects on bone are generally regarded as a beneficial side effect rather than a primary reason for therapy. Estrogens reduce the risk of hip and wrist fractures by 40% to 70% and also reduce the risk of coronary heart disease by about 50%. (Cauley JA et al. Ann Intern Med. 1995; 122: 6-16. Rich-Edwards JW. N Engl J Med. 1995; 332: 1758-1765. Gerhard M, Ganz P. Circulation. 1995; 92: 5-8.) Nevertheless, three out of four postmenopausal women shun estrogen therapy, many of them because they fear an increase in the risk of breast cancer. (See Estrogens and the Risk of Breast Cancer) Another hormone used for osteoporosis is calcitonin (Sandoz; Rhone-Poulenc Rorer). This hormone neither increases the risk of breast cancer nor reduces the risk of heart disease. Calcitonin has one major drawback: it has to be given by injection every other day, which makes it expensive and inconvenient. Currently a nasal-spray formulation is awaiting FDA approval.
Also awaiting FDA approval are a number of new drugs -- hormonal and nonhormonal -- for increasing bone density in postmenopausal women. The most promising of the nonhormonal agents are the bisphosphonates. These compounds act by adsorbing to bone crystals, rendering bone resistant to enzymatic hydrolysis and also inhibiting the activity of any osteoclasts that manage to ingest bisphosphonate-containing bone. One bisphosphonate already on the market -- etidronate (Didronel/Procter and Gamble) -- has been used for years for Paget's disease. Although not approved for postmenopausal osteoporosis, etidronate has been shown to significantly reduce the frequency of new vertebral fractures in women with osteoporosis-related vertebral fractures. (Etidronate has to be given cyclically, because continuous therapy causes mineralization defects). Second- and third-generation bisphosphonates that do not impair mineralization are available abroad and are under investigation in this country.
Recently an FDA advisory committee recommended the approval of alendronate (Fosamax/Merck), an aminobisphosphonate that has proved to be well tolerated and highly effective for inhibiting osteoclastic bone resorption without interfering with bone formation. Merck is studying alendronate, licensed from Instituto Gentili of Italy, for both postmenopausal osteoporosis and Paget's disease. Some 11,000 women worldwide are participating in clinical trials, including a 2-year study comparing alendronate with conjugated estrogens. Alendronate is approved or awaiting approval in about 35 countries.
In one 3-year multicenter study involving 994 postmenopausal women, alendronate 10 mg per day significantly increased bone mass in hip and spine (by 7.2% and 8.2%, respectively) and reduced the risk of vertebral fractures by 48% compared with placebo. Patients in the placebo group showed a 0.7% loss of bone density in hip and spine, and a greater loss of height than treated patients. (Annual meeting of the Endocrine Society, Washington DC, June 14, 1995.)
Because less than 5% of women with osteoporosis have received diagnoses and are receiving therapy, one of Merck's primary goals will be to educate women and their physicians about the importance of bone-mineral testing, an expensive procedure that requires sophisticated equipment (dual-energy X-ray absorptiometers). Merck is helping finance programs by two diagnostic equipment companies -- Hologic Inc. of Waltham, MA, and Lunar Corp. of Madison, WI -- to increase the number of bone-densitometers on the market.
Merck is also working with Ostex International Inc. of Seattle, WA. Ostex has a new urine test that indicates whether a patient is losing more bone than normal. Merck (and other companies with an eye on the osteoporosis market) may use the urine test as a marketing tool; it gives physicians a quick way to track bone loss and the effects of therapy. Another marketing strategy involves cooperation between Merck and American Home Products, maker of Premarin conjugated estrogens. Rather than competing for the same patients, American Home Products has agreed to promote alendronate along with Premarin to gynecologists, emphasizing the complementary nature of the two drugs -- alendronate for osteoporosis and Premarin for postmenopausal symptoms. (Additional information requested and received from the manufacturer.)
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