Determinants of non-compliance with bisphosphonates in women with postmenopausal osteoporosis.

OBJECTIVE

To identify determinants of non-compliance with bisphosphonates in women with postmenopausal osteoporosis. By considering the year of the introduction of weekly bisphosphonates important additional information is obtained.

METHODS

New female users of daily or weekly alendronate or risedronate between 1999 and 2004, aged >or= 45 years were identified from PHARMO RLS, including drug-dispensing and hospitalisation data of > 2 million residents of the Netherlands. One-year compliance with bisphosphonates was measured using the Medication Possession Ratio (MPR). To identify determinants of non-compliance, non-compliant women (MPR < 50%) were compared to compliant women (MPR >or= 80%). The effect of patient age, prescriber, initial dosing regimen, gastrointestinal adverse events, co-medication and fractures on non-compliance was investigated.

RESULTS

The study cohort included 8822 new users of bisphosphonates, of whom 5079 (58%) were compliant and 2720 (31%) were non-compliant after 1 year. Only 1023 women (11%) had a MPR between >or= 50% and < 80%. Daily dosing at start, increased number of co-medications and new use of intestinal agents in the year after starting bisphosphonates were independently associated with an increased odds of non-compliance. In contrast, higher age, first prescription from a specialist, osteoporosis related hospitalisation and use of NSAIDs in the year preceding bisphosphonate therapy decreased the odds of non-compliance.

CONCLUSION

This study revealed several determinants of non-compliance with bisphosphonates, the best controllable being the type of initial bisphosphonate, with daily dosing leading to more non-compliance than weekly dosing. However, compliance for both regimens is suboptimal, pointing to an unmet medical need.