2011 National Meeting

3113 — Medication Adherence as a Measure of Comparative Effectiveness in Older Patients with New-Onset Epilepsy

Zeber JE (Central Texas Veterans Health System) , Copeland LA (Central Texas Veterans Health System), Pugh MJ (VERDICT South Texas Veterans Health System)

Objectives:
Medication adherence among veterans with epilepsy remains a significant challenge, even for patients prescribed newer antiepileptic agents (AEDs), leading to increased risks of poor seizure control, re-hospitalization, and higher treatment costs. Despite substantial research identifying numerous risk factors pertaining to AED non-adherence, the role of specific medications has been neglected, as have studies focusing on older individuals. Within the context of the comparative effectiveness of epilepsy treatment, this study analyzed adherence to nine different AEDs in a national clinical sample of elderly patients with new-onset epilepsy.

Methods:
VA patients over age 66 were eligible if meeting criteria per a validated algorithm for new-onset epilepsy and AED monotherapy for at least three months. Adherence was defined by multiple measures: the medication possession ratio (MPR < 0.80 and < 0.60), a 90-day medication gap, and persistent 1-year monotherapy. Multivariable logistic regression modeled each dichotomous adherence outcome as a function of clinical and demographic measures, including overall disease and medication burden, history of dementia, current psychiatric comorbidity, and pharmacy copayment status.

Results:
The sample (N = 6,373) was primarily male (98 percent), white (78 percent), and exempt from copayments; 40 percent exhibited a prior psychiatric or dementia diagnosis. Experiencing similar rates found in younger patients, nearly half of these older veterans were poorly adherent, with rates ranging from 42-63 percent across AEDs. In multivariable models, patients on phenobarbital, valproate and gabapentin were significantly less likely to be adherent across the four outcomes (all odds ratios [OR] between 1.52 – 1.93), while lamotrigine and levetiracetam were consistently associated with better adherence (e.g., ORs of 0.69, 0.65 per the MPR outcome).

Implications:
While adherence difficulty in this elderly cohort is potentially attributable to several factors, the use of specific AEDs substantially increased this risk. Concerns of adverse events, such as cognitive difficulty or weight gain, may prove detrimental to maintaining appropriate adherence early in the treatment course.

Impacts:
Recognizing that medications cannot be effective unless taken appropriately, translating clinical utility into optimal outcomes requires incorporating the patient perspective into treatment decisions. Given comparable efficacy across AEDs, providers should consider that certain medications impart differential side effect profiles that may exacerbate adherence problems.