Missed Fosamax Dose: Use the Right Calendar for Your Prescription

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See the public record for Alendronate

Which calendar does your bottle use?

Oral alendronate comes in more than one schedule, and the strength on the label decides which one applies. The 5 mg and 10 mg tablets are taken once a day, the 35 mg and 70 mg tablets once a week, the effervescent tablet once a week, the oral solution once a week, and the 40 mg tablet once a day [2].

The Fosamax label lists 70 mg once weekly or 10 mg once daily for treating osteoporosis in postmenopausal women and in men, 35 mg once weekly or 5 mg once daily for prevention in postmenopausal women, 5 mg once daily for glucocorticoid-induced osteoporosis (10 mg daily in postmenopausal women not receiving estrogen), and 40 mg once daily for six months for Paget's disease [1].

The brand name alone will not tell you the schedule. The label notes that Fosamax is no longer marketed in the 5 mg, 10 mg, 35 mg and 40 mg strengths, or as an oral solution, although generic versions of those may still be available [1].

The weekly rule, as the label writes it

The label says to take one dose on the morning after you remember, not to take two doses on the same day, and to return to one dose once a week on the day you originally chose [1].

The timing is the morning after remembering, which is not the same as the moment you remember. The return date is your chosen weekly day, not the day the catch-up dose was taken.

Two calendars worked through

Your chosen day is Monday. You miss it and remember on Wednesday. The morning after remembering is Thursday, so Thursday morning is when the label's instruction places the dose. Your next dose stays on Monday, the day you originally chose [1]. That leaves four days between the Thursday dose and that Monday dose.

Your chosen day is Monday and you remember the missed dose on Sunday. The morning after remembering is Monday, which is already your chosen day, so one dose that Monday is all the instruction calls for [1].

The catch-up dose follows the same morning rules

A dose taken after a missed week is taken the same way as any other dose. For a tablet, the label says to take it upon arising for the day, with a full glass of 6 to 8 ounces of plain water, at least one-half hour before the first food, beverage or medication of the day; not to lie down for at least 30 minutes and until after the first food; and not to take it at bedtime or before arising [1]. Oral solution is followed by at least 2 ounces of water [1].

The Fosamax label says to wait at least 30 minutes after a dose before taking any other oral medication, because calcium supplements, antacids and oral products containing multivalent cations interfere with alendronate absorption [1].

The drink matters. Taking alendronate with coffee or orange juice reduced bioavailability by about 60%, and absorption was negligible when it was taken with or up to 2 hours after a standardized breakfast [1].

If your prescription is once daily

The Fosamax label's own missed-dose instruction covers the once-weekly schedule [1]. For a daily tablet, MedlinePlus says to skip the missed tablet and take one dose the next morning as usual, without a double dose [2].

Does one missed week matter?

The nearest large comparison tested stopping, not skipping a single dose. In FLEX, 1,099 postmenopausal women who had taken alendronate for a mean of 5 years were randomly assigned to continue (n=662) or switch to placebo (n=437) for 5 more years. Five years off alendronate lowered total hip bone mineral density 2.4% and spine bone mineral density 3.7% compared with continuing, and mean levels remained at or above pretreatment values. Nonvertebral fractures were 19% with continuing versus 18.9% with placebo, and clinical vertebral fractures were 2.4% with continuing versus 5.3% with placebo; fracture was an exploratory outcome [3].

Alendronate also leaves bone slowly. The label estimates its terminal half-life in humans at more than 10 years, reflecting gradual release from the skeleton [1].

What refill data show about gaps

In 35,537 women aged 45 and older who filled a bisphosphonate prescription, 43% were refill compliant (medication possession ratio of 0.80 or higher) and 20% stayed persistent across 24 months. Refill-compliant and persistent patients had 20% to 45% relative reductions in total, vertebral, nonvertebral and hip fractures, and the relationship grew stronger at compliance of 75% and above [4]. Refill records show dispensed supply; they do not show whether a tablet was swallowed or taken correctly.

Weekly and daily doses gave the same bone-density result

A one-year double-blind multicenter trial assigned 519 women to 70 mg once weekly, 369 to 35 mg twice weekly and 370 to 10 mg daily. Mean lumbar spine bone mineral density rose 5.1%, 5.2% and 5.4% at 12 months, and both new regimens met the prespecified equivalence criteria against daily dosing [5]. The comparison measured bone density; it was not a test of how often people forget doses.

What the label says to watch for

The label instructs patients to discontinue Fosamax and seek medical attention if they develop dysphagia, odynophagia, retrosternal pain or new or worsening heartburn [1]. The risk of severe esophageal reactions appears greater in patients who lie down after taking it, who do not swallow it with the recommended 6 to 8 ounces of water, or who keep taking it after symptoms of esophageal irritation start [1].

When missed doses keep happening

The Endocrine Society recommends reassessing fracture risk after 3 to 5 years of bisphosphonate therapy, continuing treatment in women who remain at high risk and considering a bisphosphonate holiday in those at low-to-moderate risk, with bone mineral density monitored every 1 to 3 years in high-risk individuals with low bone density [6]. The label likewise says the optimal duration of use has not been determined and that low-risk patients should be considered for discontinuation after 3 to 5 years [1].