Alendronate chemical structure
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Fosamax

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, under the name Fosavance). more...

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Pharmakokinetics

The systemic bioavailability after oral dosing is only 0.6 % as well in women and in men (fasting state). Intake together with meals and certain drinks (coffee, orange juice) further reduces the bioavailability. Soft tissues and bones are fastly reached by about 50%. After resorption in the bone alendronate has an estimated terminal halflife of 10 years; the remainder is excreted unchanged by the kidneys.

Pharmacology

Alendronate blocks osteoblast-mediated bone-resorption. It is chemically related to etidronate and the N-containing bisphosphonates such as pamidronate, which with it shares the same mode of action. Its inhibition of bone-resorption is dose-dependent and 100 to 1,000 times stronger than the equimolar effect of etidronate. Theoretically, alendronate may also inhibit bone-mineralization but this effect is 6,000 times weaker than the inhibition of bone-resorption. Under therapy normal bone tissue develops and alendronate is deposited in the bone-matrix in pharmacologically inactive form. For optimal action enough calcium and vitamin D are needed in the body. Hypocalcemia should therefore be corrected before starting therapy.

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

Contraindications and precautions

  • Acute inflammations of the gastrointestinal tract (esophagitis, gastritis, ulcerations)
  • Clinically manifest osteomalacia
  • Certain malformations and malfunctions of the esophagus (strictures, achalasia)
  • Unability to stand, walk, or sit for 30 minutes after oral administration
  • Renal impairment with a creatinine clearance below 30ml/min
  • Hypersensitivity to alendronate or another ingredient
  • Hypocalcemia
  • Pregnancy and breastfeeding
  • Patients below 18 yrs. of age, because no clinical data exists

Side-effects

  • GI tract: most prominent are harmless side effects such as mild nausea, dyspepsia, abdominal cramps, flatulence, diarrhea, or obstipation. A severe side effect is an ulceration of the esophagus caused by alendronate, which may require hospitalization and intensive treatment. Gastric and duodenal ulceration.
  • General: infrequent cases of skin rash, rarely manifesting as Stevens-Johnson syndrome and toxic epidermal necrolysis, eye problems (uveitis, scleritis) and generalized muscle, joint, and bone pain (rarely severe) have been seen. In laboratory tests decreased calcium and phosphate values may be obtained but reflect action of the drug and are harmless.
  • Osteonecrosis of the jaw, a recognised but rare side-effect of bisphosphonates

Read more at Wikipedia.org


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Studies clash on GI-event risk of bisphosphonates: Fosamax, Actonel - Gynecology
From OB/GYN News, 10/1/03 by Doug Brunk

SAN DIEGO -- Men and women older than 65 who started bisphosphonate therapy with alendronate had about a 1.5-fold greater risk for gastrointestinal events after 4 months, compared with those who started therapy with risedronate, results from a large retrospective study suggest.

In a related study, GI-related medical costs were nearly three times higher in patients who started therapy with alendronate (Fosamax) than in those who started with risedronate (Actonel), Joseph Doyle, a pharmacist, said in a poster session during the annual meeting of the American Association of Clinical Endocrinologists.

But Dr. Anastasia Daifotis told this newspaper that such studies are "extremely misleading" because they are not head-to-head randomized trials. "These are not real head-to-head comparisons," said Dr. Daifotis, who directs the Fosamax clinical trials for Merck, manufacturer of Fosamax.

Dr. Daifotis also said that the findings contradict results of the longest head-to-head randomized, placebo-controlled trial of alendronate and risedronate, which will be published soon.

For the first study, Mr. Doyle and his associates gathered data from a pharmaceutical claims database licensed by Protocare Sciences, a health care consulting service.

They conducted a retrospective analysis of 3,947 men and women aged 65 and older who were given a prescription for bisphosphonate therapy between November 2000 and August 2001.

Patients who received a prescription for risedronate (5 mg/day) or alendronate (5 mg/day, 10 mg/day, 35 mg/wk, or 70 mg/wk) were selected for analysis. Those who were prescribed a bisphosphonate during the prior 6 months were excluded.

ICD-9 diagnostic codes were used to assess the occurrence of GI events 6 months preceding the prescription and during the 4-month follow-up period, said Mr. Doyle, senior manager for health economics and outcomes research for Aventis Pharmaceuticals, manufacturer of Actonel.

Patients who took daily alendronate regimens were 57% more likely than those on risedronate to experience a GI event in the first 4 months after initiating therapy. Patients who took weekly alendronate regimens, meanwhile, were 66% more likely than those on risedronate to experience a GI event in the first 4 months.

In addition, patients who started therapy with risedronate were 23% more likely than patients on daily alendronate and 15% more likely than patients on weekly alendronate to have had a history of GI diagnoses before the initiation of treatment.

"This suggests a possible preference for prescribing risedronate among high-risk GI patients," Mr. Doyle said.

The findings run counter to results of the longest head-to-head randomized, placebo-controlled trial of alendronate and risedronate, which are slated to appear in Current Medical Research and Opinion, Dr. Daifotis said.

The 1-year, multicenter study of 549 patients found no difference in the prevalence of GI events: 27% in the placebo group, 28% in the risedronate group, and 28% in the alendronate group. "They're pretty comparable," she said.

In the second study presented at the meeting, Mr. Doyle and his associates used the same database to evaluate direct medical costs of GI-related events, including outpatient visits, hospitalization, and prescriptions for gastroprotective agents.

The average monthly per-patient cost for GI-related medical treatment was $2.52 for risedronate, $7.40 for alendronate daily, and $7.50 for alendronate weekly, he said.

"The alendronate patient costs were three times greater than [those of] the risedronate patients, irrespective of whether patients received daily or weekly alendronate," Mr. Doyle said. Inpatient care was the main reason for the difference, he added.

For her part, Dr. Daifotis dismissed the value of the study.

It "tells you nothing about how they made sure that the treatment groups had the same patient characteristics," she said. "If you end up with all of your alendronate patients being sicker then I would not be surprised if they were hospitalized more or that their [medical] costs were greater."

The studies were funded by the Alliance for Better Bone Health, a partnership between Procter & Gamble and Aventis.

Doug Brunk

San Diego Bureau

COPYRIGHT 2003 International Medical News Group
COPYRIGHT 2003 Gale Group

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