Research Activities, September 2013
Adherence to osteoporosis medications decreases fracture risk
Prior studies have demonstrated that adherence to osteoporosis medications reduces the risk of fractures. A new study has examined this relationship to see whether this reduction is due to the specific pharmacologic effects of these drugs or instead to the healthy adherer effect, in which patients who adhere to their medications may differ in important ways from patients who do not take their medications as directed.
The study found that the association between medication adherence and fracture risk differed by medication exposure, suggesting little role for the healthy adherer effect.
Researchers selected persons who had osteoporosis and had experienced a fracture from a 5 percent sample of Medicare enrollees aged 65 years or older. The investigators then identified which of these patients had begun taking biphosphonates for osteoporosis, selective serotonin reuptake inhibitors (SSRIs) for depression (which can increase the risk of fractures), or angiotensin-converting enzyme (ACE) inhibitors or calcium-channel blockers for hypertension during the 9 months after their fracture.
Adherence was assessed 6 months after the start of a medication using the medication possession ratio (MPR). The MPR is the percentage of time a patient has access to medication as determined by refill and pill count. The researchers also examined patients’ fractures of the hip, spine, arm (from the shoulder to the elbow), and wrist. Good adherence to bisphos-phonates was significantly associated with a low rate of hip and major fractures. Patients with the highest fracture rates among those taking bisphosphonates had an MPR of less than 50 percent. Those patients most adherent to SSRIs had higher fracture rates than experienced by their less adherent counterparts, but the differences were not statistically significant.
According to the researchers, if there were any healthy adherer effect present, it did not impair the ability to detect the possibility of an association between SSRI use and high fracture risk. However, the rates of fracture were comparable for adherent and nonadherent patients taking ACE inhibitors and calcium channel blockers, with no important healthy adherer effect present in this group. The study was supported in part by AHRQ (HS18517).
See "Does medication adherence itself confer fracture protection? An investigation of the healthy adherer effect in observational data," by Jeffrey R. Curtis, M.D., M.S., M.P.H., Huifeng Yun, Ph.D., Jeff L. Lange, Ph.D., and others in the December 2012 Arthritis Care & Research 64(12), pp. 1855-1863.