Bisphosphonate Compliance No Better Weekly Than Daily


NASHVILLE, TENN. — Women with postmenopausal osteoporosis are no more likely to adhere to bisphosphonate therapy with weekly dosing than with daily dosing, according to data presented in a poster at the annual meeting of the American Society for Bone and Mineral Research.

In a retrospective study of 12,538 women with postmenopausal osteoporosis, risk of adherence failure did not differ between patients receiving weekly versus daily bisphosphonate therapy, according to Derek Weycker, Ph.D., of Policy Analysis Inc. in Brookline, Mass., and his colleagues.

The researchers reviewed integrated medical and outpatient pharmacy claims for women aged 45 years and older with postmenopausal osteoporosis from 30 U.S. health plans. Claims from January 1998 to December 2003 were included in the review.

Women were determined to have postmenopausal osteoporosis based on one or more medical claims with a corresponding diagnosis code. The women also had no evidence of secondary causes of osteoporosis. Patients were considered to have initiated therapy if their first corresponding prescription was preceded by a 6-month period of continuous health benefits without evidence of antiosteoporosis drug use.

Adherence was assessed on a daily basis from the date of therapy initiation through the date of a switch to another antiosteoporosis drug or formulation, date they left the plan, or Dec. 31, 2003—whichever came first. An adherence ratio was calculated by dividing the cumulative number of bisphosphonate therapy days by the number of elapsed calendar days (from therapy initiation). To calculate these measures, the researchers identified all outpatient pharmacy claims for weekly and daily bisphosphonate therapy based on corresponding codes from the National Drug Code system, arrayed them temporally based on dispensing dates, and assessed days of therapy supplied for each script based on the quantity of pills dispensed.

Within 6 months of initiating therapy, 57% of the 9,117 women on weekly therapy and 62% of the 3,421 women on daily therapy were considered to have adherence failure—defined as an adherence ratio less than 80%.

At 1 year, 66% of those on weekly therapy and 71% of those on daily therapy had adherence failure. At 2.5 years, the rates were 80% for weekly therapy and 82% for daily therapy.

After adjusting for age, fracture history, drug received, selected comorbid conditions, and selected concomitant medications, the two groups did not differ in risk of adherence failure. Risk of adherence failure was higher among women aged 65 years and older but was lower in those with a history of fracture.

The researchers did not assess adherence for specific drugs.

The research was funded by Amgen Inc., which is currently investigating a fully monoclonal antibody for the treatment of osteoporosis.

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