Adherence to Oral Migraine Prophylaxis Medications in Patients with Chronic Migraine
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<bold>BACKGROUND</bold> <br> Migraine is an episodic neurological disorder that affects 12% of Americans and millions worldwide. Chronic migraine (CM) as ≥15 headache days per month with ≥8 days per month that meet criteria for migraine, for more than three months, with each episode lasting greater than four hours. CM is a disabling disorder that has been shown to significantly reduce quality of life and leaves many patients unable to perform daily activities. Patients with frequent headaches, such as those suffering from CM, may benefit from prophylactic treatment. Oral prophylactic agents require adherence to various dosing regimens in order to adequately reduce the burden of migraine. Although adherence has been well studied among migraine patients, only one study has investigated adherence using claims databases in this population. To date, no study has examined adherence to prophylactic therapy among the chronic migraine population using real world data from large claims databases such as MarketScan. <br> <bold>OBJECTIVE</bold> The aim of this study is to describe the chronic migraine population through a large US insurance claims database from 2008 to 2011 and to assess adherence, switching, and resource use among patients taking oral migraine prophylactics. <bold>METHODS</bold> Data were obtained from MarketScan® Research Databases, which contain inpatient, outpatient, and pharmacy claims for patients covered by commercial, Medicare, and Medicaid insurance plans in the US. Databases were queried for patients 18 years and older who were diagnosed with CM and who initiated an oral migraine prophylactic agent between January 1, 2008 and December 31, 2011. Drugs included in the analysis were those representative of the three main classes of medications used in migraine prophylaxis: antidepressants (amitriptyline, nortriptyline, citalopram, escitalopram, sertraline, fluoxetine, paroxetine), beta blockers (propranolol, metoprolol, nadolol, atenolol), and anti-seizure (gabapentin, topiramate, divalproex) medications. Adherence to migraine prophylactic agents among the CM patient population were calculated with both medication possession ratios (MPR) and proportion of days covered (PDC). Switch rate was reported as the proportion of patients for whom was recorded a pharmacy claim for one of the 13 medications of interest within 30 days prior to or 60 days post discontinuation of the initial prophylactic. Proportion of patients with one or more ER visits for migraine stratified by prophylactic medication and adherence rates (both MPR and PDC). Bivariate analyses were conducted to compare patient demographics among patients taking each medication; and separately between patients who were and were not adherent. T-tests and chi-2 tests were used to estimate means and standard deviations for continuous data and or proportions for categorical variables, respectively. Unadjusted and adjusted comparisons were made using logistic regression models for adherence and ER visits. <br> <bold>RESULTS</bold> <br> In the MarketScan Databases, we identified 47,555 patients who had a diagnosis of chronic migraine between 2008 and 2011. After applying inclusion/exclusion criteria there were 1,640 patients included in the analysis of the 6-month follow-up cohort and 861 patients in the 12-month follow-up cohort. The majority of patients were female with a mean age approximately 40 years old. Preferred provider organization (PPO) health insurance was the most common plan type and a large portion of patients were working full time. Approximately 30% of patients were adherent at the end of 6 months and 14% at 12 months when ≥80% MPR was used to measure adherence. Using PDC to calculate adherence provided even lower estimates of 24% and 14% for 6 and 12 months follow-up, respectively. The most common prophylactic switched to and from was topiramate. A large proportion of the patients who switched decided to replace amitriptyline and nortriptyline with another prophylactic, while an equally large proportion of patients who switched chose to convert to citalopram, gabapentin, or propranolol. At 6 months, the proportion in the non-adherent group who experienced an ER visit is smaller than the proportion who experienced an ER visit in the adherent group. At 12 months, the proportions are similar between the adherent and non-adherent groups. Regression models were not statistically significant for any of the outcomes. <br> <bold>CONCLUSION</bold> Adherence to oral migraine prophylactics is low among the US chronic migraine population at both 6 and 12 months. A large proportion of patients switch between the prophylactics studied with the greatest switching occurring to and from topiramate. A significant proportion of chronic migraine patients experience ER visits but in our results we found that these visits were not associated with adherence.