Standardizing the measurement of drug exposure

Transcription

1 Standardizing the measurement of drug exposure The ability to determine drug exposure in real-world clinical practice enables important insights for the optimal use of medicines and healthcare resources. With significant potential for treatment complexities to confound the measurement process, finding valid approaches to standardization can be key to meaningful results. Here we consider a recent case study in asthma. The author Christopher Blanchette, PHD, MS, MA is Principal HEOR, IMS Health Cblanchette@us.imshealth.com ACCESSPOINT VOLUME 2 ISSUE 4 PAGE

2 INSIGHTS DRUG EXPOSURE MEASUREMENT Standardizing the measurement of drug exposure A case study in asthma The measurement of drug treatment exposure can be complex, based on the underlying assumptions that drive the product s use. These are most easily encountered with the classic 30-day prescription fills of oral medications. However, in cases where medications are prescribed as needed, where various routes of administration apply, or where dosing is inconsistent across diverse generics manufacturers, the accurate measurement of drug exposure becomes significantly more involved. STUDY DESIGN CAPTURING DATA All three of these issues were encountered in a series of studies assessing short-acting beta agonists (SABA) exposure as a predictor of subsequent asthma-related s, most notably dealing with as-needed prescribing of SABA in either a metered dose inhaler (MDI) or in a nebulized inhalant form.,2,3,4,5 This retrospective analysis included both prevalent and incident asthmatics, to assess patients with various levels of severity during the available observation period (Figure ). For all analyses, evaluations were performed for three groups: all subjects (ages 6-56 years), pediatrics (ages 6-7 years) and adults (ages 8-56 years). Data were obtained on subjects enrolled in a health plan that participated in the PharMetrics Patient-Centric Database between July, 2003 and June 30, The database comprises information from enrollment files as well as facility, professional service and out-patient pharmacy claims, from a variety of private healthcare benefit plans. Its coverage extends to more than 40 million patients enrolled in over 70 health plans across the US, with health plans providing data on a continuous basis. The number of plans contributing to the PharMetrics FIGURE : RETROSPECTIVE STUDY DESIGN Baseline and medical characteristics assessed Q SABA use Q2 Q2 SABA use Q3 Q3 SABA use Q4 Q Q2 Q3 Q4 year pre-index period Index year post-index period date PAGE 2 IMS HEOR AND REAL-WORLD EVIDENCE SOLUTIONS

3 dataset has increased over time. Demographic information (excluding race and ethnicity) is available for all patients. Most plans also provide information on dates of eligibility for medical and out-patient pharmacy benefits. Data available for each out-patient pharmacy claim ( prescription ) included the drug dispensed (in National Drug Code [NDC] format) and the dispensing date. Most plans also provided information on the quantity and number of therapy days dispensed. Data available for each facility or professional service claim ( medical claim ) include dates of service and International Classification of Diseases 9th Edition, Clinical Modification (ICD-9-CM) diagnosis codes and ICD-9-CM procedure codes (facility claims) or Current Procedural Terminology, Version 4 (CPT-4) procedure codes (professional service claims). All plans provided information on payments. Most plans also provided information on billed charges. Payments were imputed for claims with missing payment information (due to capitation arrangements). All claims for any given person could be linked using a unique encrypted identifier. The dataset is fully de-identified and HIPAA compliant. The criteria applied for the study population were as follows: Inclusion Patients aged 6 56 years on the index date Continuous enrollment in a health plan in the database for 2 years Claim with asthma diagnosis (ICD-9 code 493.XX) Claim for either a SABA or any asthma controller medication in each of the pre-index and post-index periods Exclusion Any diagnosis of COPD, emphysema, chronic bronchitis, or bronchiectasis Subjects with diagnoses requiring frequent oral corticosteroid (OCS) use Subjects with a diagnosis of respiratory tract cancer DRUG EXPOSURE EVALUATION APPROACH Since pharmacy use can only be identified in the PharMetrics dataset using National Drug Codes (NDC), the first step was to compile an exhaustive list of NDCs for each drug of interest. The starting point for this was to link the list of identified brand and proprietary drug names to the in-house, composite drug dictionary. SABA dosing exposure standardization was determined through prior studies. These included the 2002 evaluation by Glauber and Fuhlbrigge which provided a compelling argument for using a canister-equivalent measure, comprised by inhaled and nebulized SABA, instead of just simple counts of medication. 6 They introduced a scheme for standardizing doses of inhaled and nebulized SABA equivalent to two inhalations of albuterol, dispensed from a metered dose inhaler (MDI) as the standard for comparison. Using a high threshold level of >8 SABA canisters (counts method) or >8 canister-equivalents, the canister-equivalent method increased the population identified as having high SABA use by 39% (6.6% vs..9%) relative to the simple-count method. continued on next page ACCESSPOINT VOLUME 2 ISSUE 4 PAGE 3

4 INSIGHTS DRUG EXPOSURE MEASUREMENT Hospitalization ED/UC Visit OCS claim Any of the above Thus, in studies that do not recognize the use of nebulized SABA there is likely to be substantial misclassification of patient based on high SABA utilization. The present study utilized the method described by Chan, et al, 7 being inclusive of almost all MDI and nebulized SABA types identified in the dataset. Canister equivalents were determined for each claim represented. A standard SABA canister size was defined to be one containing 200 metered actuations, which encompassed more than 97% of MDI SABA claims. More than 96% of total SABA MDI claims were for albuterol; 2.2% were for pirbuterol; and.6% were for levalbuterol. In the case of pirbuterol, whose standard dispensing contains 400 actuations, claims were set to two canisters. Levalbuterol was considered to be equivalent in potency to albuterol. In cases where insufficient information was available to make the determination, canister size was imputed using days supply of medication. Thirty days supply or less was determined to be equivalent to one canister, 3 to 60 days supply as two canisters, etc. FIGURE 2: SABA CANISTER FILLS 2ND QUARTER (POST-INDEX YEAR) N=93,444 0 Canisters 2-3 Canisters > 3 Canisters Canisters (n=59,653) Percentage of Patients 2-3 Canisters (n= 26,525) > 3 Canisters (n= 4,266) 32% 5% 64% FIGURE 3: Q3 EXACERBATION INCIDENCE BY Q2 SABA USE STRATA ED = Emergency department UC = Urgent care OCS = Oral corticosteroid Nebulized SABA canister claims comprised 2% of all SABA claims. Based on the Chan study method, canister-equivalents were derived for each nebulized SABA claim. The vast majority of these claims were for albuterol or levalbuterol (considered equivalent in potency to albuterol), in which case one 3ml ampule was equivalent to 0.02 canister-equivalents, making fifty ampules of 3ml of medication equivalent to one canister. The quantity of medicine is typically given in ml in the dataset. Each ampule typically contains 3ml of medicine and is most often dispensed in boxes of 24, 25 or 30, each of which was equated to a half canister of SABA. It was determined that the most accurate method to represent these medication quantities was to round to the nearest halfcanister because most boxes contained 24, 25 or 30 ampules and most claims were in multiples of these. Less than % of claims observed were clear outliers (eg, >80 ampules). For these, the maximum dose was capped at three canister equivalents per claim. Due to the heterogeneity of asthma controller medications, it was elected to use annual days supply during the pre-index and post-index years, and days supply per quarter for the quarterly analysis regardless of the medication being inhaled (eg, ICS) or oral (eg, leukotriene modifiers). Controller medications prescribed concomitantly and measured as covariates were assessed as the sum of days supply provided on the claims, a proxy for days of exposure. A similar method was used to describe use of nasal steroid sprays and antibiotics. PAGE 4 IMS HEOR AND REAL-WORLD EVIDENCE SOLUTIONS

5 FIGURE 4: RISK OF EXACERBATIONS BY Q2 SABA STRATA (REFERENCE=0 CANISTERS) Hospitalization ED/UC Visit OCS claim Any of the above 2 3 ED = Emergency department UC = Urgent care OCS = Oral corticosteroid Odds Ratio (95% CI) All oral corticosteroid (OCS) claims, regardless of days supplied, were counted as one claim. Ninety percent of prescription dispensing for OCS was found to be for 2 days or less. In the analysis, OCS were evaluated as a binary variable for the presence of one or more claims, and as a count of claims during the specified time period. Injectable corticosteroids were not captured, since these are typically administered in a physician s office and are rarely registered as NDC-based claims. CONCLUSIONS The study found that a quarterly assessment of SABA utilization can be used to identify patients at for asthma-related s. The incidence of an asthma was associated with greater SABA use in the previous quarter (Figures 2,3,4).Variability in SABA exposure measurement and standardization between nebulized and MDI routes may have provided biased estimates on associated cost and asthma-related s. Notwithstanding this caveat, however, these findings provided critical insights for optimizing the treatment and management of asthma patients. Blanchette CM, Silver H, Petersen H, Kamble S, Meddis D, Gutierrez B. Quarterly assessment of short-acting ß-agonist use as a predictor of subsequent healthcare services use for asthmatics in the US. ISPOR 4th Annual International Meeting, Orlando, FL; May 6-20, Blanchette CM, Silver H, Petersen H, Kamble S, Meddis D, Gutierrez B. Identification of a threshold for high utilization of short-acting ß2-agonists in a commercially insured adult asthmatic population in the United States. American Academy for Asthma, Allergy, and Immunology 2009 Annual Meeting, Washington, DC; March 3-7, Silver H, Blanchette CM, Petersen H, Kamble S, Meddis D, Gutierrez B. Short-acting beta agonist utilization and of asthma among a commercially insured pediatric population in the United States. American Academy for Asthma, Allergy, and Immunology 2009 Annual Meeting; Washington, DC; March 3-7, Silver HS, Blanchette CM, Kamble S, Petersen H, Letter M, Meddis D, Gutierrez B. Relationship between short-acting ß2-adrenergic agonist use and healthcare costs. American Journal of Managed Care. 20 Jan; 7(): Silver HS, Blanchette CM, Kamble S, Petersen H, Letter M, Meddis D, Gutierrez B. Quarterly assessment of short-acting ß2-adrenergic agonist use as a predictor of subsequent health care use for asthmatic patients in the United States. Journal of Asthma. 200 Aug; 47(6): Glauber JH, Fuhlbrigge AL. Stratifying asthma populations by medication use: How you count counts. Ann Allergy Asthma Immunol. 2002; 88: Chan J, Hui RL, Spence MM. Effects on resource utilization of adding salmeterol in combination or separately to inhaled corticosteroids. J Manag Care Pharm. Jan-Feb 2007; 3():2-27. ACCESSPOINT VOLUME 2 ISSUE 4 PAGE 5