P-167 MP-12: Evaluation of antihypertensive medication adherence in a Veteran population

• Published in: American journal of hypertension Vol. 18; no. S4; p. 67A
• Main Authors: Lopez, Julio R., Meier, Joy L., Siegel, David
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.05.2005
• Subjects: Medication Adherence; Pharmacoepidemiology
• ISSN: 0895-7061; 1941-7225; 1879-1905
• DOI: 10.1016/j.amjhyper.2005.03.185

This study evaluates antihypertensive medication adherence using Department of Veterans Affairs pharmacy databases. Automated data extraction routines capture pharmacy, ICD-9, laboratory, and patient demographic data on a monthly basis. We included patients with a diagnosis of hypertension (ICD-9 codes 401.1 to 401.9) who had a history of medication use during July 2002 through December 2003. Medications in the following drug classes were studied: thiazides (TZ), beta blockers (BB), ACE inhibitors (ACE), angiotensin receptor blockers (ARB), calcium channel antagonists (CA) and alpha blockers (AB). We excluded patients with serum creatinine of >2.5 and those receiving K sparing diuretics alone. The first date of prescription filling for each patient within the date range is the index date from which fill and refill dates are collected for one year to calculate posession ratio (MTOT) and days out of medication ratio (MOUT). Data elements for analysis are medication class as listed above, patient's age, gender, ethnicity, VA facility, and co-diagnosis with diabetes, schizophrenia/psychosis, and dementia. The potential effect of these variables on adherence were examined using logistic regression analysis with patients categorized as adherent if MTOT is 80% or greater. In the six VA classes there were 79,055 patients with average age per group ranging from 67.4–72.9 years. 97% were male and when ethnicity was recorded 74.5% were Caucasian, 14% African-American and 5% each Hispanic and Asian. The largest number of patients (22,233) took an ACE whereas a small number used ARB (3,729). Unadjusted adherence rates based on MTOT ranged from 77.9% for TZ to 83.3% for ARB (p<0.01). Similar findings were noted using the MOUT parameter. 8% of patients using an ACE had at least two ICD9 codes for diabetes as compared to 4.6% getting TZ. A dementia and a schizophrenia/psychosis diagnosis occurred in each drug class in up to 3.3% and 3.4% of patients, respectively. Drug class and age were independent predictors of adherence with odds ratios of 1.019 and 1.014, respectively. We conclude that adherence rates with antihypertensive medications are remarkably high. Although there are statistical differences by drug class, these differences are small.