1041 — Anticonvulsant Medication Use and Risk of Fractures among Older VA Patients

Mezuk B (University of Michigan, Ann Arbor Serious Mental Illness Treatment Research and Evaluation Center), Morden NE (Dartmouth Institute for Health Policy and Clinical Practice; Dartmouth Medical School), Ganoczy D (Ann Arbor HSR&D; VHA Serious Mental Illness Treatment Research and Evaluation Center), Post EP (VHA Serious Mental Illness Treatment Research and Evaluation Center), Kilbourne AM (Serious Mental Illness Treatment Research and Evaluation Center, Ann Arbor HSR&D)

Objectives:
Many medications used to treat serious mental illness have been associated with alterations in bone metabolism and fracture risk. Older adults with bipolar disorder (BD) may be particularly susceptible to such adverse events because of their higher burden of comorbid medical conditions. The aims of this study were to investigate the association between anticonvulsant use and fracture and to evaluate the impact of diagnosed BD on this association.

Methods:
Prospective cohort study of all patients diagnosed with BD identified from the VA National Psychosis Registry in FY2002, and a random sample of veterans receiving care through the VA, all age 50 and older (N = 98,514). Cox proportional hazards modeling was used to evaluate the relative hazard (HR) between duration of anticonvulsant use in FY02 and FY03 and fracture risk over the follow-up period (FY04-06). Interaction terms and subgroup analyses were used to determine whether the association differed for patients with BD.

Results:
There were 3,469 incident fractures over the study period, 1,798 among patients with BD. Duration of anticonvulsant use was associated with fracture risk in a dose-response manner relative to never use (HR: < 6 months: 1.38, 6-12 months: 1.49, and 12+ months: 1.64, all p < 0.05). Among BD patients, risk of fracture associated with these medications was weaker, although still significant, relative to the rest of the cohort (HR for 12+ months for non-BD: 1.54 vs. 1.20 for BD, both p < 0.001). Antidepressants were also associated with fracture risk among BD patients, although the magnitude of both these associations was weaker than that for anticonvulsants.

Implications:
Anticonvulsant use is associated with fracture among older veterans, including those with BD. Use of other medications and dosage variation compared to other indications for anticonvulsant use may explain the weaker relationship observed among BD patients.

Impacts:
BD affects over 80,000 VA patients in a given year, and is associated with substantial functional impairment. Anticonvulsants are commonly prescribed as mood stabilizers and use of these medications is associated with risk of fracture. VA providers should screen and monitor older patients taking anticonvulsants for remediable coexistent risk factors for fracture. Decision aids and guidelines could prove valuable in this effort.