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Defining Adherence and Persistence Sapna N. Patel UCSF Pharm. D. Candidate 2008 Preceptor Dr. Craig S. Stern March 21, 2008 Pictures Relevance Evaluating adherence & persistence is necessary for accurate assessment of: Cost-effectiveness of therapy Quantifying drug exposure in a population over time Drug Utilization Patterns for Formulary Development Identifying appropriate therapy for patients Assessing clinical outcomes of treatment Prior Authorization Criteria Impact of A&P Low adherence & persistence Increased morbidity & mortality Increased health-care costs “Forgiveness”: therapeutic effects of drug therapy despite noncompliance Proposed Definitions International Society for Pharmacoeconomics and Outcomes Research (ISPOR) Adherence (compliance): the extent to which a patient acts in accordance with the prescribed interval & dose of a dosing regimen Persistence refers to the act of continuing treatment for the prescribed duration Treatment adherence & persistence together contributes to overall drug effectiveness CMS Definitions Current Issues Multiple definitions and measurement models Hinder health outcomes & cost-effectiveness analysis Prevent comparisons of different studies Standardized definition would: Help develop more effective strategies to enhance medication related A&P and decrease health-care costs Measures of Adherence Direct Indirect Desired observation or study evaluation period “Between fills” periods Treatment Gaps Direct Methods Method Directly Observed Therapy Medicine or Metabolite Blood Levels Pros Most accurate Objective Cons Time consuming Impractical Hiding pills Expensive Metabolism variation White coat adherence Biologic Markers in blood Objective Time consuming Expensive Indirect Methods Method Questionnaires, selfreporting Prescription rate refills Pros Cons Cost-effective Subjective Time consuming Useful in clinical setting Infrequent Objective Expensive visits = increased error Metabolism variation White coat Adherence Pill Counts Objective Subjective Easy-to-do Easily Quantitative results altered by patient Measuring Adherence: Medication Possession Ratio (MPR) MPR = total days’ supply X 100 total # days evaluated 353/365 X 100 = fill in% Equals overall percent adherence value (medication availability) MPR (cont) Pros: Easy to calculate Widely used adherence measure Cons: Participants get >1 fill in one day (ex: vacation supply) Change in prescribing directions Refills occur close to study termination “Between Fills” Measures Days Between Fills Adherence Rate (DBR) DBR =1- total days’ supply – last days’ supply last claim date – 1st claim date X 100 Refill Compliance Rate (RCR) RCR = last claim date – 1st claim date Compliance Rate (CR) CR = (last claim date – 1st claim date) – total days’ supply total days’ supply X 100 last claim date – 1st claim date Medication Possession Ratio, Modified (MPRm) MPRm = total days’ supply (last claim date – 1st X 100 claim date) + last days’ supply X 100 “Between Fills” Measures Pros: Helps accounts for cutoff examination date period Consistent results seen with denominator of total study evaluation period Cons: In cases of single refills Smaller denominator Cannot assess/overestimation of adherence Treatment Gaps total gap days CMG = total days’ study participation – total days’ supply total days’ study participation Continuous Measure of Medication Gaps (CMG) :Provides time patient does not have medication available (%) Ex: (362-365)/362 = 0.00 or -0.01 Range: 0.0 = complete adherence 1.0 = complete non-adherence (-) values = surplus days (due to early refill or overfill) Measuring Persistence Minimum-Refills Model Proportion of Days Covered Model Refill Sequence Model Anniversary Model Minimum-Refills Model Persistence: Pt being dispensed a minimum # of Rx’s per year Minimum-Refills Model Pros: Might be useful for describing “as needed” medication use Cons: Does not account for length of time between refills Does not account for amount of time each refill should last Proportion-of-Days-Covered Model Persistence: Enough medication dispensed to cover a specified proportion of days within a fixed interval (ex: 1 year) Example: 210 days’ supply/365 day interval = 58% PDC during the 1st year Proportion-of-Days-Covered Model Pros: Relies on uniform evaluation period for all patients Shorter follow-up times create bias in PDC (higher numbers) Fewer opportunities for noncompliance/nonpersistence Cons: Cut-off arbitrary No info about timeliness of refilling or persistence Refill-Sequence Model PG: Permissible gap Persistence: total duration of a continuous sequence of refills Unacceptable gap: Interval between the date of the 1st Rx and refill considered to be nonpersistence Refill-Sequence Model Pros: Permit switches between Rxs with same indication Increased accuracy of measuring persistence when Information can be used to assess effect of an intervention aimed at improving persistency Cons: May not consider all refilling behavior across the observation period. Once an individual is classified as nonpersistent, future refilling behavior is no longer considered Patient could have discontinued or PG not well defined switched medications Anniversary Model 4 Fills Monthly Fill Persistence: Rx refilled within a specified interval (e.g., +/- 30 days) surrounding the anniversary of 1st Rx Both patients are persistent at 1 year Patient 1: more consistent Anniversary Model Pros: Simple to use Accurate method for timeliness of medication refilling IF small refill gaps are small Cons: No consideration given to refills within the 1year interval Patient is persistent, but not necessarily adherent Summary References Osterberg L, Blaschke T. Adherence to Medication. N Engl J Med 2005;353;5:487-497. Caetano PA, Lam JMC, Morgan SG. Toward a standard definition and measurement of persistence with drug therapy: Examples from research on statin and antihypertensive utilization. Clin Therapeutics 2006;28:1411-1424. Cramer JA, Roy A, Burrell A, et al. Medication compliance and persistence: Terminology and definitions. Value Health 2008;11. [Epub June 25, 2007] Sikka R, Xia F, Aubert RE. Estimating medication persistency using administrative claims data. Am J Managed Care 2005;11:449-457. Hess LM, Raebel MA, Conner DA, Malone DC. Measurement of adherence in pharmacy administrative databases: A proposal for standard definitions and preferred measures. Ann Pharmacother 2006;40:1280-1288. Hughes D, Cowell W, Koncz T, Cramer JA. Methods for integrating medication compliance and persistence in pharmacoeconomic evaluations. Value Health 2007;10(6):498-509. www.cms.org assessed March 20, 2008.