1

Alendronate sodium is an osteoporosis medicine commonly recommended as a once-a-week 70 mg dose.

Why not 35 mg twice a week? or 10 mg daily? I am guessing that a more steady intake like this would be just as effective but is not recommended simply because daily doses means a daily burden (e.g., avoiding food, avoiding lying down, within one hour of taking the medicine).

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Actually, according to the official drug label found here, 3 out of 5 indications allow several dosage regimens that include those you asked about:

2.1 Treatment of Osteoporosis in Postmenopausal Women
The recommended dosage is:

  • one 70 mg tablet once weekly
    or
  • one bottle of 70 mg oral solution once weekly
    or
  • one 10 mg tablet once daily

2.2 Prevention of Osteoporosis in Postmenopausal Women
The recommended dosage is:

  • one 35 mg tablet once weekly
    or
  • one 5 mg tablet once daily

2.3 Treatment to Increase Bone Mass in Men with Osteoporosis
The recommended dosage is:

  • one 70 mg tablet once weekly
    or
  • one bottle of 70 mg oral solution once weekly
    or
  • one 10 mg tablet once daily

Also, check out this paper. It compared the efficacy and safety of treatment with oral once-weekly alendronate 70 mg (N=519), twice-weekly alendronate 35 mg (N=369), and daily alendronate 10 mg in a one-year, double-blind, multicenter study of postmenopausal women (ages 42 to 95) with osteoporosis.
The findings indicate that "both of the new regimens fully satisfied the equivalence criteria relative to daily therapy", which means that the first dosage regimen was 10 mg/day, which has later been altered for higher dose over a longer interval for increasing compliance.

And the reason that it doesn't really matter which dosage regimen you will adopt is probably related to alendronate's ridiculously long half-life, due to its tendency to concentrate in the bones and seep out very very slowly. So it has been calculated that 10 mg/day is the daily dose you need to enjoy the desired effect, and since the drug accumulates in the bones, its serum concentrations over relatively short time intervals (e.g., days) do not matter, so you can choose whichever way you want to take the drug, provided that you adhere to the correct dose you should be taking every time you take your dose.

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