Department of Health and Human Services

OFFICE OF 

INSPECTOR GENERAL 

 

Daniel R. Levinson 

Inspector General 

December 2008 

OEI-05-07-00490 

 

COMPARING SPECIAL NEEDS 

PLAN BENEFICIARIES TO OTHER 

MEDICARE ADVANTAGE 

PRESCRIPTION DRUG PLAN 

BENEFICIARIES 
Office of Inspector General 

http://oig.hhs.gov 

The mission of the Office of Inspector General (OIG), as mandated by Public Law 95-452, as 

amended, is to protect the integrity of the Department of Health and Human Services 

(HHS) programs, as well as the health and welfare of beneficiaries served by those 

programs. This statutory mission is carried out through a nationwide network of audits, 

investigations, and inspections conducted by the following operating components: 

Office of Audit Services 

The Office of Audit Services (OAS) provides auditing services for HHS, either by conducting 

audits with its own audit resources or by overseeing audit work done by others. Audits 

examine the performance of HHS programs and/or its grantees and contractors in carrying 

out their respective responsibilities and are intended to provide independent assessments of 

HHS programs and operations. These assessments help reduce waste, abuse, and 

mismanagement and promote economy and efficiency throughout HHS. 

Office of Evaluation and Inspections 

The Office of Evaluation and Inspections (OEI) conducts national evaluations to provide 

HHS, Congress, and the public with timely, useful, and reliable information on significant 

issues. These evaluations focus on preventing fraud, waste, or abuse and promoting 

economy, efficiency, and effectiveness of departmental programs. To promote impact, OEI 

reports also present practical recommendations for improving program operations. 

Office of Investigations 

The Office of Investigations (OI) conducts criminal, civil, and administrative investigations 

of fraud and misconduct related to HHS programs, operations, and beneficiaries. With 

investigators working in all 50 States and the District of Columbia, OI utilizes its resources 

by actively coordinating with the Department of Justice and other Federal, State, and local 

law enforcement authorities. The investigative efforts of OI often lead to criminal 

convictions, administrative sanctions, and/or civil monetary penalties. 

Office of Counsel to the Inspector General 

The Office of Counsel to the Inspector General (OCIG) provides general legal services to 

OIG, rendering advice and opinions on HHS programs and operations and providing all 

legal support for OIG’s internal operations. OCIG represents OIG in all civil and 

administrative fraud and abuse cases involving HHS programs, including False Claims Act, 

program exclusion, and civil monetary penalty cases. In connection with these cases, OCIG 

also negotiates and monitors corporate integrity agreements. OCIG renders advisory 

opinions, issues compliance program guidance, publishes fraud alerts, and provides other 

guidance to the health care industry concerning the anti-kickback statute and other OIG 

enforcement authorities. 
 

ΔINTRODUCTION EXECUTIVE SUMMARY 

OBJECTIVE

To compare Special Needs Plan (SNP) beneficiaries to other Medicare 

Advantage Prescription Drug Plan (MA-PD) beneficiaries regarding 

drug utilization, drug costs, and exposure to potentially inappropriate 

drug pairs. 

BACKGROUND 

Congress created the SNP authority to allow Medicare managed care, 

known as Medicare Advantage (MA) plans, to develop targeted clinical 

programs to care more effectively for high-risk beneficiaries. Among 

other services, SNPs offer prescription drug coverage. Any MA plan 

that offers Part D prescription drug coverage is known as an MA-PD. 

Since SNPs became available in 2006, the number of SNPs and SNP 

beneficiary enrollment have grown rapidly. Policymakers have focused 

their attention on SNPs because of this growth and because SNPs, like 

other MA plans, cost more per beneficiary than fee-for-service Medicare. 

In particular, policymakers have questioned whether SNPs are 

providing specialized care for special needs individuals. 

Because SNPs target special needs individuals who are more likely to 

have complicated medical regimens, SNP beneficiaries may have an 

increased risk of exposure to therapeutic duplications or drug-drug 

interactions. Therapeutic duplications occur when two drugs that treat 

the same medical condition, taken together, increase the risk of toxicity. 

Drug-drug interactions occur when two drugs taken together lead to 

increased toxicity or changes in the efficacy of one or both drugs. 

Therapeutic duplications and drug-drug interactions may be prescribed 

or dispensed in error or may be part of a clinically appropriate drug 

regimen. Regardless, they have the potential to lead to an adverse drug 

event (ADE). An ADE may involve temporary or moderate side effects 

or can have serious consequences, including disability or death. 

Because therapeutic duplications and drug-drug interactions can lead to 

ADEs they may require monitoring or a change in drug regimen. 

Throughout the report, we refer to therapeutic duplications and 

drug-drug interactions, when aggregated, as potentially inappropriate 

drug pairs. 

We used Medicare Part D prescription drug data to compare SNP 

beneficiaries to other MA-PD beneficiaries regarding drug utilization, 

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EXECUTIVE SUMMARY 

costs, and exposure to potentially inappropriate drug pairs during 2006. 

Prescription drug data are the only encounter-level data available for 

comparing SNP beneficiaries to other MA-PD beneficiaries. 

FINDINGS 

On average, SNP beneficiaries had higher prescription drug 

utilization and costs than other MA-PD beneficiaries. On average, 

SNP beneficiaries filled 11 percent more prescriptions than other 

MA-PD beneficiaries in 2006. In addition, the average annual 

prescription cost per SNP beneficiary was 49 percent higher compared 

to that of other MA-PD beneficiaries. The difference in average annual 

prescription drug cost per beneficiary between SNPs and other MA-PDs 

appears to be because of SNP beneficiaries’ higher utilization, 

utilization of costlier drugs, lower utilization of less costly 90-day 

prescriptions, and SNPs paying more on average than MA-PDs for some 

highly utilized drugs. 

Despite SNP beneficiaries’ higher rates of drug utilization, SNP and 

other MA-PD beneficiaries were similarly exposed to potentially 

inappropriate drug pairs. Although SNP beneficiaries filled 11 percent 

more prescriptions than other MA-PD beneficiaries on average, the 

same percentage of both SNP and other MA-PD beneficiaries were 

exposed to potentially inappropriate drug pairs. In addition, at higher 

levels of drug utilization, SNP beneficiaries were less likely to be 

exposed to a potentially inappropriate drug pair than other MA-PD 

beneficiaries. 

The majority of potentially inappropriate drug pairs were drug-drug 

interactions of moderate risk for both SNP and other MA-PD 

beneficiaries. The frequency and severity of potentially inappropriate 

drug pairs were similar for SNP and other MA-PD beneficiaries during 

2006. Sixty-five percent of potentially inappropriate drug pairs for both 

SNP and other MA-PD beneficiaries were drug-drug interactions, 

83 percent of which were of moderate risk. In addition, the majority of 

potentially inappropriate drug pairs for both SNP and other MA-PD 

beneficiaries recurred and involved drugs prescribed by the same 

physician and filled by the same pharmacy. 

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EXECUTIVE SUMMARY 

RECOMMENDATION 

The Centers for Medicare & Medicaid Services should help SNPs 

and other MA-PDs provide physicians and pharmacists the 

information they need to prevent inappropriate drug pairs leading to 

ADEs. The number of potentially inappropriate drug pairs prescribed 

and dispensed to Medicare beneficiaries could be reduced if physicians 

and pharmacists have access to accurate and targeted information 

regarding inappropriate drug pairs for the Medicare population. The 

Centers for Medicare & Medicaid Services (CMS) should continue to 

encourage plans to fully implement an e-prescribing program that 

improves information physicians and pharmacists have about 

beneficiaries’ medication histories. In addition, CMS should provide 

plans information on inappropriate drug pairs most likely to lead to 

severe or serious ADEs in the Medicare population. Finally, CMS should 

encourage plans to provide tools to assist physicians and pharmacists in 

appropriately analyzing and using the information they receive. 

AGENCY COMMENTS AND OFFICE OF INSPECTOR GENERAL 

RESPONSE 

CMS concurred with our recommendation to help SNPs and other 

MA-PDs provide physicians and pharmacists the information they need 

to prevent inappropriate drug pairs that could lead to ADEs. CMS noted 

that Part D sponsors are currently required to maintain systems to 

monitor drug utilization, including the use of potentially inappropriate 

drug pairs. 

In addition, CMS expressed concern about our use of the First Databank 

drug product information database to identify potentially inappropriate 

drug pairs. CMS stated that First Databank algorithms have not been 

specifically validated for use in the Medicare population. Although this 

may be true, First DataBank is widely used by pharmacists, researchers, 

and health care plans, including the Department of Veterans Affairs, 

State Medicaid programs, and Part D sponsors, to identify inappropriate 

drug pairs. 

 
Δ TABLE OF CONTENTS 

EXECUTIVE SUMMARY .....................................i

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

FINDINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

Special Needs Plan beneficiaries’ drug utilization and costs were 

higher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

Exposure to potentially inappropriate drug pairs was the 

same . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

 Moderate drug-drug interactions occurred most frequently . . . . . 15 

RECOMMENDATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

Agency Comments and Office of Inspector General Response . . . 21 

APPENDIXES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

 A: Detailed Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

 B: Differences in Cost for the Most Frequently Dispensed 

 Prescription Drugs in Special Needs Plans . . . . . . . . . . . . . . . 29 

 C: Drugs Most Frequently Involved in Severe and Serious 

Potential Drug-Drug Interactions . . . . . . . . . . . . . . . . . . . . . . 31 

 D: Agency Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
 

Δ INTRODUCTION 

OBJECTIVE 

To compare Special Needs Plan (SNP) beneficiaries to other Medicare 

Advantage Prescription Drug Plan (MA-PD) beneficiaries regarding 

drug utilization, drug costs, and exposure to potentially inappropriate 

drug pairs. 

BACKGROUND 

Since Special Needs Plans (SNP) became available in 2006, the number 

of SNPs and SNP beneficiary enrollment have grown rapidly. 

Policymakers have focused their attention on SNPs because of this 

growth and because SNPs, like other Medicare managed care plans, cost 

the Federal Government more per beneficiary than fee-for-service 

Medicare. In particular, policymakers have questioned whether SNPs 

are providing specialized care for special needs individuals.1 For these 

reasons, Congress placed a moratorium on the entry of new SNPs into 

Medicare from January 1, 2008, through December 31, 2009.2 This 

moratorium provides additional time to study SNPs. 

We used Medicare Part D prescription drug data to compare SNP 

beneficiaries to other MA-PD beneficiaries regarding drug utilization, 

costs, and exposure to potentially inappropriate drug pairs during 2006. 

Prescription drug data are the only encounter-level data available for 

comparing SNP beneficiaries to other MA-PD beneficiaries. Thus, the 

comparisons provided in this report offer insights into the population of 

beneficiaries enrolled in SNPs versus other MA-PD beneficiaries. 

Medicare Managed Care 

Effective January 1, 2006, the Medicare Prescription Drug, 

Improvement, and Modernization Act of 2003 (MMA): (1) established 

the Medicare Advantage (MA) program to replace the Medicare + Choice 

program,3 (2) added new MA plan types,4 (3) changed MA payment 

1 153 Cong. Rec. S15834, 15835 (daily ed. Dec. 18, 2007) (Statement of Sen. Grassley). 

2 Medicare, Medicaid, and SCHIP Extension Act of 2007, P.L. No. 110-173 § 108, Social 

Security Act, § 1851 note, 42 U.S.C. § 1395w-21 note. 

3 MMA, P.L. No. 108-173 § 201, Social Security Act, § 1851 note, 42 U.S.C. 

§ 1395w-21 note. 

4 MMA, P.L. No. 108-173 § 221, Social Security Act, § 1859(b), 42 U.S.C. § 1395w-28(b). 

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INTRODUCTION 

methodology,5 and (4) provided qualified prescription drug coverage 

under Medicare Part D (Part D).6 

Special Needs Plans 

Congress created the SNP authority to allow MA plans to develop 

targeted clinical programs to care more effectively for high-risk 

beneficiaries.7 The SNP, a type of MA plan, may restrict enrollment to 

one or more classes of special needs individuals.8 In contrast, all other 

MA plans are prohibited from restricting enrollment based on 

beneficiary health status.9 

Special needs individuals are MA-eligible individuals who are:10

• institutionalized or require an equivalent level of care,11 

• eligible for both Medicare and Medicaid (dual eligible), or 

• suffering from a severe disability or have disabling chronic conditions 

and meet such other requirements as set by the Secretary.12

Congress initially authorized SNPs to target enrollment of special 

needs individuals through December 2008.13 In 2008, Congress 

extended the SNP authorization through December 2010.14 However, 

Congress also extended the moratorium on the designation of other 

MA plans as SNPs, originally in place through December 31, 2009, to 

December 31, 2010.15

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5 MMA, P.L. No. 108-173 § 211, Social Security Act, § 1853(c)(1), 42 U.S.C. 

§ 1395w 23(c)(1). 

6 MMA, P.L. No. 108-173 § 101, Social Security Act, § 1860D-1, 42 U.S.C. § 1395w-101. 

7 H.R. Rep. No. 108-391, at 555 (2003) (Conf. Rep.). 

8 Social Security Act, § 1859(f), 42 U.S.C § 1395w-28(f). 

9 Social Security Act, § 1851(g), 42 U.S.C. § 1395w-21(g). 

10 MA-eligible individuals are both entitled to Medicare Part A and enrolled in Medicare 

Part B. Social Security Act, § 1851(a)(3), 42 U.S.C. §1395w-21(a)(3). 

11 Centers for Medicare & Medicaid Services (CMS), “MA Special Needs Plan Guidance.” 

January 19, 2006. Available online at 

http://www.cms.hhs.gov/SpecialNeedsPlans/Downloads/FinalSNPGuidance1-19-06R1.pdf. 

Accessed on June 30, 2008. 

12 Social Security Act, § 1859(b)(6)(B), 42 U.S.C. § 1395w-28(b)(6)(B). 

13 MMA, P.L. No. 108-173 § 231, Social Security Act, § 1859(f), 42 U.S.C. § 1395w-28(f). 

14 Medicare Improvements for Patients and Providers Act of 2008, P.L. No. 110-275 

§ 164, Social Security Act, § 1859(f) note, 42 U.S.C. § 1395w-28(f). 

15 Medicare Improvements for Patients and Providers Act of 2008, P.L. No. 110-275 

§ 164, Social Security Act, § 1851 note, 42 U.S.C. § 1395w-21 note. 

P LAN BENEFICIARIES
 

INTRODUCTION 

Before the moratorium, the number of SNPs and SNP beneficiary 

enrollment increased rapidly. In 2006, there were 276 SNPs.16 

By 2008, there were 769 SNPs.17 Over this same period, SNP 

beneficiary enrollment increased over 102 percent. As of July 2008, 

over 1.2 million beneficiaries were enrolled in SNPs.18 

In addition, SNPs, like other MA plans, continue to cost the Federal 

Government more per beneficiary than fee-for-service Medicare. The 

Medicare Payment Advisory Committee (MedPAC) has projected that 

SNPs will cost 15 percent more, and all MA plans 13 percent more, 

per beneficiary than fee-for-service Medicare in 2008.19

Prescription Drug Coverage by SNPs and Other MA-PDs 

MA plans that offer prescription drug coverage under Part D are 

referred to as MA-PDs.20 All SNPs must offer prescription drug 

coverage and are therefore MA-PDs.21 More than 8 million beneficiaries 

were enrolled in MA-PDs as of July 2008, including the over 1.2 million 

beneficiaries enrolled in SNPs.22 

The Federal Government, through CMS, pays a portion of basic drug 

coverage through a monthly prospective direct subsidy payment to 

MA-PDs.23 CMS adjusts MA-PD payments based on the estimated 

impact of enrollees’ health on plans’ costs using the Part D Hierarchical 

Condition Category risk adjustment model to calculate beneficiaries’ 

Part D risk scores. The higher a beneficiary’s risk score, the higher the 

payment is for that beneficiary. 

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16 CMS, “Special Needs Plans – Fact Sheet & Data Summary.” Available online at 

http://www.cms.hhs.gov/SpecialNeedsPlans/Downloads/FSNPFACT.pdf. Accessed on 

March 27, 2008. 

17 CMS, “SNP Comprehensive Report,” July 2008. Available online at 

http://www.cms.hhs.gov/MCRAdvPartDEnrolData/Downloads/SNP-200807.zip. Accessed on 

July 28, 2008. 

18 Ibid. 

19 MedPAC, “Report to the Congress: Medicare Payment Policy March 2008,” 

pp. 246–247. Available online at 

http://www.medpac.gov/documents/Mar08_EntireReport.pdf. Accessed on March 3, 2008. 

20 42 CFR § 422.2. 

21 Ibid. 

22 CMS, “Monthly Contract and Enrollment Summary Report,” July 2008. Available 

online at 

http://www.cms.hhs.gov/MCRAdvPArtDEnrolData/Downloads/Contract%20Summary%20-

%20July%202008.zip. Accessed on July 28, 2008. 

23 42 CFR § 423.329(a)(1). 

P LAN BENEFICIARIES
 

INTRODUCTION 

Beneficiaries are typically responsible for paying a monthly premium, a 

deductible, and copayments for each prescription they fill.24 However, 

beneficiaries with limited income and assets who meet certain 

requirements are eligible to receive assistance to pay for out-of-pocket 

costs associated with their prescription drug coverage.25 Most SNP 

beneficiaries are dual eligibles (beneficiaries enrolled in both Medicare 

and Medicaid) who are automatically deemed eligible for this 

assistance.26 27

Therapeutic Duplication and Drug-Drug Interaction 

Therapeutic duplication occurs when the combined dose of two drugs 

from the same therapeutic class (i.e., groups of drugs that treat the 

same medical condition) increases the risk of toxicity. Drug-drug 

interaction occurs when two drugs taken together lead to a clinically 

significant toxicity or when one drug interferes with the effectiveness of 

the other. 

Therapeutic duplication and drug-drug interaction may be the result of 

a medication error or may be part of a clinically appropriate drug 

regimen. Regardless, they have the potential to lead to an unexpected 

or dangerous reaction, called an adverse drug event (ADE). Thus, they 

may require monitoring or a change in drug regimen. Throughout the 

report, we refer to therapeutic duplication and drug-drug interaction, 

when aggregated, as potentially inappropriate drug pairs. 

An ADE may involve temporary or moderate side effects such as nausea 

or a rash, or can have serious consequences including patient death or 

serious disabilities.28 More severe ADEs could result in emergency 

department visits, hospital admissions, or death.29 Among Medicare 

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24 Social Security Act, § 1860D-2, 42 U.S.C. § 1395w-102; and Social Security Act, 

§ 1860D-13, 42 U.S.C. § 1395w-113. 

25 Social Security Act, § 1860D-14, 42 U.S.C. § 1395w-114. 

26 CMS, “SNP Comprehensive Report,” July 2008. Available online at 

http://www.cms.hhs.gov/MCRAdvPartDEnrolData/Downloads/SNP-200807.zip. Accessed on 

July 28, 2008. 

27 Social Security Act, § 1860D-14, 42 U.S.C. § 1395w-114. 

28 Adverse Drug Events: Substantial Problem but Magnitude Uncertain: Hearing 

Before the U.S. Senate Committee on Health, Education, Labor, and Pensions, 

106th Cong. 3 (2000) (Statement of Janet Heinrich, Associate Director for Health Financing 

and Public Health Issues, Health and Human Services Division, U.S. Government 

Accountability Office). Available online at http://www.gao.gov/new.items/he00053t.pdf. 

Accessed on March 27, 2008. 

29 Ibid. 

P LAN BENEFICIARIES
 

INTRODUCTION 

enrollees, more than 1.9 million ADEs and more than 

180,000 life-threatening or fatal ADEs occur each year. It is estimated 

that more than 25 percent of ADEs and 50 percent of life-threatening or 

fatal ADEs are preventable.30 

SNP beneficiaries may be at an increased risk of potentially 

inappropriate drug pairs leading to ADEs. Age, severity of illness, and 

the number of prescribed drugs have been associated with a higher risk 

of ADEs.31 SNP beneficiaries typically have chronic illnesses and 

multiple medical conditions that may require more drugs than other 

Medicare beneficiaries.32

Prescription Drug Safeguards and Safety Initiatives 

CMS requires all MA-PDs, including SNPs, to implement two 

safeguards designed, in part, to reduce ADEs and improve medication 

use: quality assurance systems and medication therapy management 

(MTM) programs.33 In addition, CMS encourages e-prescribing as a 

means of preventing ADEs.34 Finally, the Food and Drug 

Administration (FDA) is using Medicare Part D prescription drug data 

as part of the initiative to monitor drug safety.35 

Quality assurance systems aim to protect beneficiaries, reduce ADEs, 

and improve medication use by reviewing beneficiaries’ medications 

through concurrent and retrospective drug utilization review systems. 

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30 Jerry H. Gurwitz, et al., 2003. “Incidence and preventability of adverse drug events 

among older persons in the ambulatory setting.” Journal of the American Medical 

Association, vol. 289(9), pp. 1107–1116. 

31 Agency for Healthcare Research and Quality, “Reducing and Preventing Adverse Drug 

Events to Decrease Hospital Costs.” Available online at 

http://www.ahrq.gov/qual/aderia/aderia.htm. Accessed on September 21, 2007. 

32 National Health Policy Group Memorandum, “Performance Measures for Special 

Needs Plans.” Available online at 

http://www.nhpg.org/media/3014/snpalliancedsnpperfromancemeasures.pdf. Accessed on 

October 9, 2007. 

33 42 CFR §423.153. 

34 CMS, “E-Prescribing Tools To Help Prevent Adverse Drug Interactions Press Release,” 

April 2, 2008. Available online at 

http://www.cms.hhs.gov/apps/media/press/release.asp?Counter=3025&intNumPerPage=10&

checkDate=&checkKey=&srchType=1&numDays=3500&srchOpt=0&srchData=&keywordT

ype=All&chkNewsType=1%2C+2%2C+3%2C+4%2C+5&intPage=&showAll=&pYear=&year

=&desc=false&cboOrder=date. Accessed on June 18, 2008. 

35 CMS, “New Efforts to Help Improve Medical Products for Patient Safety and Quality 

of Medical Care,” May 22, 2008. Available online at 

http://www.hhs.gov/news/press/2008pres/05/20080522a.html. Accessed on August 27, 2008. 

P LAN BENEFICIARIES
 

INTRODUCTION 

Concurrent drug utilization review systems screen for potential drug 

therapy problems at a drug’s point of sale and alert pharmacists to 

potentially inappropriate drug pairs before the drugs have been 

dispensed to the patient. Retrospective drug utilization reviews are 

periodic examinations that may be used to identify potentially 

inappropriate drug pairs after the drugs have been dispensed. 

MTM programs educate beneficiaries about the potential risks of their 

prescribed drug combinations.36 At a minimum, a plan’s MTM program 

must target enrollees who have multiple chronic diseases, are taking 

multiple Part D drugs, and are likely to incur annual costs for covered 

Part D drugs that exceed $4,000.37 Beyond these minimum standards, 

plans have significant flexibility in determining their targeted 

populations and designing the services their MTM programs provide 

and how they provide them. 

In addition, CMS promotes the use of e-prescribing, anticipating that it 

will help reduce the number of ADEs for Medicare beneficiaries. Once 

e-prescribing is fully implemented, it has the potential to reduce ADEs 

by allowing plans, physicians, and pharmacists to efficiently 

communicate about the prescription drugs a beneficiary is taking.38 To 

encourage its adoption, CMS established standards for e-prescribing 

under Part D, including standards related to formulary and benefits, 

medication history, fill status notification, and identification of 

individual health care providers.39

Finally, through its Sentinel Initiative, FDA will create a system to 

monitor the performance of prescription drugs, as well as medical 

devices, for potential problems such as ADEs. This initiative will link 

Medicare Part D prescription drug data, which became available to 

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36 CMS, “Medicare Prescription Drug Manual,” ch. 7, § 30.1. Available online at 

http://www.cms.hhs.gov/PrescriptionDrugCovContra/Downloads/PDBManualChap7Quality.

pdf. Accessed on April 11, 2008. 

37 CMS, “Medicare Prescription Drug Manual,” ch. 7, § 30.2. Available online at 

http://www.cms.hhs.gov/PrescriptionDrugCovContra/Downloads/PDBManualChap7Quality.

pdf. Accessed on April 11, 2008. 

38 CMS, “E-Prescribing Tools To Help Prevent Adverse Drug Interactions Press Release,” 

April 2, 2008. Available online at 

http://www.cms.hhs.gov/apps/media/press/release.asp?Counter=3025&intNumPerPage=10&

checkDate=&checkKey=&srchType=1&numDays=3500&srchOpt=0&srchData=&keywordT

ype=All&chkNewsType=1%2C+2%2C+3%2C+4%2C+5&intPage=&showAll=&pYear=&year

=&desc=false&cboOrder=date. Accessed on June 18, 2008. 

39 73 Fed. Reg. 18918 (Apr. 7, 2008). 

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INTRODUCTION 

Federal agencies in May 2008, with Medicare inpatient and outpatient 

data in an attempt to identify ADEs that occurred.40 Although MA-PD 

inpatient and outpatient data are not collected by CMS and are not 

included in the initiative, FDA will have access to the Medicare Part D 

prescription drug data for more than 25 million beneficiaries. 

Office of Inspector General and Related Work 

The Kaiser Family Foundation issued a study in January 2008 that 

concluded that SNPs’ value was uncertain, stating that further 

information was essential for assessing them.41 In addition, Congress 

mandated a report from CMS concerning SNPs, to be completed no later 

than December 31, 2007.42 Congress required that the report assess the 

cost and quality of services SNPs provide to beneficiaries. As of 

September 2008, the report has yet to be released. 

The Institute of Medicine issued a congressionally mandated report in 

July 2006 on the nature and causes of medication errors and ADEs, 

their impact on patients, and other issues concerning them in the 

national population.43 The study found that the rates of medication 

errors and preventable ADEs are high, but that effective strategies to 

prevent medication errors and ADEs, such as e-prescribing, physician 

and patient education, and pharmacist involvement, are available. 

The Tax Relief and Health Care Act of 2006 requires the Inspector 

General to report to Congress regarding the incidence of “never events” 

(preventable serious adverse events) for Medicare beneficiaries, 

including types of events and payments by any party.44 This report is 

one in a series that the Office of Inspector General is conducting 

concerning adverse events for Medicare beneficiaries, including those 

that occur in hospitals. This report explores potentially inappropriate 

drug pairs that may lead to ADEs. 

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40 CMS, “New Efforts to Help Improve Medical Products for Patient Safety and Quality 

of Medical Care,” May 22, 2008. Available online at 

http://www.hhs.gov/news/press/2008pres/05/20080522a.html. Accessed on August 27, 2008. 

41 J.D. Verdier, et al., “Do We Know If Medicare Advantage Special Needs Plans Are 

Special?” Medicare Issue Brief, The Henry J. Kaiser Foundation, January 2008. Available 

online at http://www.kff.org/medicare/upload/7729.pdf. Accessed on April 14, 2008. 

42 MMA, P.L. No. 108-173 § 231, Social Security Act § 1851 note, 42 U.S.C. 

§ 1395w-21 note. 

43 Philip Aspden, et al., Institute of Medicine of the National Academies, “Preventing 

Medication Errors: Quality Chasm Series,” 2007. 

44 The Tax Relief and Health Care Act of 2006, P.L. No. 109-432 § 203. 

P LAN BENEFICIARIES
 

INTRODUCTION 

METHODOLOGY 

This study compares SNP beneficiaries’ drug utilization, cost, and 

exposure to potentially inappropriate drug pairs to those of other 

MA-PD beneficiaries. These comparisons provide insights into the 

population of beneficiaries enrolled in SNPs and other MA-PDs using 

measures related to prescription drug use. 

Scope 

This study does not analyze SNP or other MA-PD efforts to manage 

prescription drug use or to reduce beneficiaries’ exposure to potentially 

inappropriate drug pairs. Instead, our analysis focuses on comparing 

SNP beneficiaries to other MA-PD beneficiaries. Prescription drug data 

are the only encounter-level data available for Medicare managed care 

plans. These data allow for a comparison of SNP beneficiaries to other 

MA-PD beneficiaries, but do not allow for a comparison of plans’ 

programs for managing prescription drug use. 

We limited our analysis to therapeutic duplications and drug-drug 

interactions. We focused on these because they are evident through 

prescription drug data and because they are defined in accepted 

industry resources. 

Data Sources 

We used three data sources to conduct this study: (1) 2006 Part D 

Prescription Drug Event (PDE) data, (2) August 2007 First DataBank 

drug product information data, and (3) 2006 CMS plan-level descriptive 

data. 

CMS requires plans providing prescription drug coverage to submit 

PDE data for payment purposes. Each drug event included in these 

data represents the dispensing of a drug or a medical supply for the 

injection of insulin. 

For more information on our data sources and other aspects of our 

methodology, see Appendix A. 

Data Analysis 

We analyzed all prescriptions for 634,000 SNP beneficiaries and 

5.8 million other MA-PD beneficiaries in 2006. We used First 

DataBank to obtain product information for each prescription and 

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INTRODUCTION 

CMS’s plan-level descriptive data to determine whether plans were 

SNPs or other MA-PDs. 

Calculating prescription drug utilization. To assess beneficiary drug 

utilization within SNPs versus that in other MA-PDs in 2006, we 

calculated the average number of prescriptions filled per beneficiary. 

We used PDE data, normalized by the number of days that the 

prescriptions covered, to calculate the number of prescriptions filled by 

beneficiaries. We considered PDE data with days of supply less than or 

equal to 44 days as one prescription. PDE data with days of supply 

greater than 44 but less than or equal to 74 were counted as two 

prescriptions. PDE data with days of supply greater than 74 were 

counted as three prescriptions. 

We also determined which drugs were most frequently dispensed to 

SNP and other MA-PD beneficiaries during 2006. We based our count 

of drugs on the Ingredient List Identifier for each drug. The Ingredient 

List Identifier represents a unique combination of active ingredients, 

regardless of manufacturer, package size, dosage form, route of 

administration, or strength. This identifier does not distinguish 

whether a drug is the generic or brand name version. 

Calculating prescription drug costs. We calculated the prescription drug 

costs incurred by SNPs and other MA-PDs on behalf of their 

beneficiaries at the point of sale. We did not calculate net costs because 

they are not captured in the PDE data. To calculate the cost of 

prescription drugs, we used the ingredient cost field provided in the 

PDE data, which represents the cost of the drug. It does not include 

any additional administrative costs, such as the dispensing fee paid to 

pharmacies. 

Using these data, we calculated the average annual prescription drug 

cost per beneficiary for SNPs and other MA-PDs. We also calculated the 

average cost per prescription for both SNP and other MA-PD 

beneficiaries, the overall average cost per prescription for the most 

frequently dispensed drugs for SNP and other MA-PD beneficiaries, and 

the average cost paid by SNPs and other MA-PDs for the most 

frequently dispensed drugs for SNP beneficiaries. 

Calculating potential therapeutic duplications and drug-drug interactions. 

For our analysis of potential therapeutic duplications and drug-drug 

interactions, we did not include beneficiaries who filled prescriptions 

under more than one plan. We did this to avoid counting potential 

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INTRODUCTION 

therapeutic duplications and drug-drug interactions involving drugs 

from two different plans. Excluding these 400,000 beneficiaries left 

534,000 SNP beneficiaries and 5.5 million other MA-PD beneficiaries in 

our analysis of potential therapeutic duplications and drug-drug 

interactions. 

To determine when potential therapeutic duplications occurred, we used 

First DataBank’s Duplicate Therapy Module. This module provides 

information on whether duplication within a therapeutic class increases 

the risk of toxicity. 

To determine when potential drug-drug interactions occurred, we used 

First DataBank’s Drug-Drug Interaction Module. First DataBank uses 

a system of flags to identify when two drugs potentially interact if taken 

simultaneously and assigns each interaction a severity level. See 

Table 1 for more detail on First DataBank’s severe, serious, and 

moderate severity levels. 

Table 1: Severity Levels of Drug-Drug Interactions 

Severity 

Level Description of Interaction 

Severe These medicines are not usually taken together. Contact health care 

professional (e.g., doctor or pharmacist) for more information. 

Serious These medicines may interact and cause very harmful effects. 

Contact health care professional for more information. 

Moderate These medicines may cause some risk when taken together. 

Contact health care professional for more information. 

Source: First DataBank Drug-Drug Interaction Module, 2007.

Data Limitations 

This study only identifies potential therapeutic duplications and 

drug-drug interactions. It does not determine whether these potentially 

inappropriate drug pairs were prescribed or dispensed purposefully or 

in error. In addition, this study does not determine that beneficiaries 

took the drugs they were dispensed nor whether beneficiaries who took 

the drugs experienced any ill effects. Thus, this study does not 

determine that an ADE occurred. Rather, the potential therapeutic 

duplications and drug-drug interactions identified in this report are 

instances in which drug pairs created the circumstances in which an 

ADE could occur and thus may have required monitoring by a health 

care professional. 

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INTRODUCTION 

This study uses only one source of information, First DataBank, to 

identify potential therapeutic duplications and drug-drug interactions. 

First DataBank is widely used by pharmacists and researchers as a tool 

for obtaining drug information, including alerts for therapeutic 

duplications and drug-drug interactions. However, individual plans 

may use other databases and tools that may identify potential 

therapeutic duplications or drug-drug interactions differently from First 

DataBank. 

We did not independently verify the First Databank modules’ accuracy 

in identifying potential therapeutic duplications and drug-drug 

interactions in the Medicare population. Further, we did not compare 

First DataBank to other sources for identifying potential therapeutic 

duplications and drug-drug interactions. 

Standards 

This study was conducted in accordance with the “Quality Standards 

for Inspections” issued by the President’s Council on Integrity and 

Efficiency and the Executive Council on Integrity and Efficiency. 

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On average, SNP beneficiaries filled 

11 percent more prescriptions and 

had 49 percent higher average 

prescription drug costs than other 

MA-PD beneficiaries in 2006. SNP beneficiaries’ higher prescription 

drug utilization and costs indicate that they may be different from other 

MA-PD beneficiaries, at least as far as their drug utilization and costs 

are concerned. 

On average, SNP beneficiaries had higher 

prescription drug utilization and costs than 

other MA-PD beneficiaries 

Δ FINDINGS 

On average, SNP beneficiaries filled 11 percent more prescriptions than 

other MA-PD beneficiaries 

On average, SNP beneficiaries filled 40 prescriptions during 2006. 

Other MA-PD beneficiaries filled 36 prescriptions on average during 

2006. In addition, 25 percent of SNP beneficiaries filled 

56 prescriptions or more, compared to 21 percent of other MA-PD 

beneficiaries. 

SNP beneficiaries filled, on average, five prescriptions per month during 

2006. Other MA-PD beneficiaries filled, on average, between four and 

five prescriptions per month. 

Overall, 93 percent of prescriptions were refills during 2006. For SNP 

beneficiaries, 90 percent of prescriptions were refills; for other MA-PD 

beneficiaries, 93 percent were refills. Frequent refills indicate the use of 

maintenance drugs for chronic conditions rather than drugs to treat 

acute episodes. 

On average, the annual prescription drug cost per SNP beneficiary was 

49 percent higher than that of other MA-PD beneficiaries 

The average annual prescription drug cost per SNP beneficiary was 

$2,104 in 2006, with most beneficiaries’ prescription drug costs ranging 

between $390 and $2,600. In comparison, other MA-PD beneficiaries 

had an average annual prescription drug cost of $1,411 per beneficiary. 

In fact, 79 percent of other MA-PD beneficiaries had annual prescription 

drug costs that were below the SNP beneficiaries’ average annual 

prescription drug cost of $2,104. 

The fact that SNP beneficiaries’ average annual prescription drug cost 

was higher than other MA-PD beneficiaries’ may be partially explained 

by drug utilization. As previously indicated, SNP beneficiaries filled, on 

average, four more prescriptions than other MA-PD beneficiaries. 

In addition, the average cost per prescription for SNP beneficiaries was 

greater than that for other MA-PD beneficiaries. On average, SNP 

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FINDINGS 

beneficiaries’ prescriptions cost $53 compared to $39 for other MA-PD 

beneficiaries. The fact that SNP beneficiaries’ average cost per 

prescription was higher than that of other MA-PD beneficiaries may be 

explained by SNP beneficiaries’ utilization of costlier drugs, their low 

utilization of less-expensive 90-day prescriptions, and the prices 

negotiated between plans and pharmacies. 

SNP beneficiaries used drugs that were somewhat different from, and 

more costly than, those used by other MA-PD beneficiaries. For 

example, there were nine drugs that differed when comparing the 

40 drugs most frequently dispensed to SNP beneficiaries and other 

MA-PD beneficiaries. Using the overall average prescription drug cost 

as a measure of market value, the nine drugs found only on the SNP list 

of top drugs were more expensive drugs. The overall average cost per 

prescription for these nine drugs was $86, compared to $22 for the 

nine drugs found only on the list of top drugs used by other MA-PD 

beneficiaries. 

In addition, SNP beneficiaries had a lower utilization of 90-day 

prescriptions. Only 1 percent of SNP beneficiaries’ prescriptions were 

for 90 days compared to 14 percent for other MA-PD beneficiaries. 

These extended prescriptions cost 57 percent less per day than 30-day 

prescriptions. SNP beneficiaries’ low utilization of 90-day prescriptions 

may be an intentional strategy by SNPs to more closely monitor their 

special needs population. 

Finally, in some cases, SNPs paid pharmacies more for the same drug 

than other MA-PDs. For example, SNPs paid more per prescription 

than other MA-PDs for 34 of the 40 drugs most frequently dispensed to 

SNP beneficiaries. SNPs paid as much as 52 percent more than other 

MA-PDs for these drugs. See Appendix B for a breakout of this analysis 

by prescription drug. 

SNPs may have paid more for some drugs than other MA-PDs because 

of differences in negotiating power, either because SNPs are not part of 

larger organizations or because they have lower enrollment. Lack of 

affiliation with larger organizations and lower enrollment translates 

into less market share to use as a tool to bargain for lower drug prices. 

Overall, SNPs typically have lower enrollment than other MA-PDs. In 

fact, for 2008, 63 percent of SNPs have fewer than 500 beneficiaries 

enrolled in their plans. 

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FINDINGS 

Because SNP beneficiaries filled 

more prescriptions for more drugs 

than other MA-PD beneficiaries, 

they might be expected to be at 

greater risk of exposure to 

potentially inappropriate drug pairs. The greater the drug utilization 

and the more different drugs a beneficiary takes, the greater the 

opportunity for exposure to potentially inappropriate drug pairs. SNP 

beneficiaries filled 11 percent more prescriptions than other MA-PD 

beneficiaries, on average. In addition, on average, SNP beneficiaries 

filled prescriptions for 10 different drugs while other MA-PD 

beneficiaries filled prescriptions for 8 different drugs. Despite this 

higher drug utilization, the same percentage of SNP beneficiaries were 

exposed to at least one potentially inappropriate drug pair as other 

MA-PD beneficiaries. Fifty-three percent of both SNP and other MA-PD 

beneficiaries were exposed to at least one potential therapeutic 

duplication or drug-drug interaction, which may or may not have led to 

an ADE. 

Despite SNP beneficiaries’ higher rates of drug 

utilization, SNP and other MA-PD beneficiaries 

were similarly exposed to potentially 

inappropriate drug pairs 

At higher levels of prescription drug utilization, SNP beneficiaries were less 

likely to be exposed to a potentially inappropriate drug pair than other 

MA-PD beneficiaries 

In general, exposure to potentially inappropriate drug pairs is positively 

correlated to the number of prescriptions filled by beneficiaries. As 

utilization increased, a greater percentage of SNP and other MA-PD 

beneficiaries were exposed to at least one potentially inappropriate drug 

pair. However, at higher levels of prescription drug utilization, SNP 

beneficiaries were less likely than other MA-PD beneficiaries to be 

exposed to a potentially inappropriate drug pair. For example, 

67 percent of SNP beneficiaries who filled between 41 and 

60 prescriptions were exposed to a potential therapeutic duplication or 

drug-drug interaction, compared to 77 percent of other MA-PD 

beneficiaries. The chart on the following page illustrates that SNP 

beneficiaries were less likely to be exposed to a potential therapeutic 

duplication or drug-drug interaction than other MA-PD beneficiaries at 

higher levels of prescription drug utilization. 

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FINDINGS 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1–20 21–40 41–60 61–80 81+

Number of Prescriptions During 2006

Percentage of Beneficiaries

SNPs

Other MA-PDs

Chart 1: Percentage of SNP and Other MA-PD Beneficiaries Exposed to a Therapeutic

Duplication or Drug-Drug Interaction for Ranges of Prescriptions

Source: Office of Inspector General (OIG) analysis of 2006 PDE data, 2008.

The type and severity of the 

potentially inappropriate drug 

pairs SNP and other MA-PD 

beneficiaries were exposed to were 

similar during 2006. Over half of 

potentially inappropriate drug pairs for both SNP and other MA-PD 

beneficiaries were drug-drug interactions, most of which were of 

moderate risk. 

The majority of potentially inappropriate drug 

pairs were drug-drug interactions of moderate 

risk for both SNP and other MA-PD beneficiaries 

For both SNP and other MA-PD beneficiaries, the majority of potentially 

inappropriate drug pairs were drug-drug interactions 

Drug-drug interactions accounted for 65 percent of potentially 

inappropriate drug pairs for both SNP and other MA-PD beneficiaries. 

The remaining 35 percent of potentially inappropriate drug pairs were 

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FINDINGS 

therapeutic duplications. On average, SNP and other MA-PD 

beneficiaries who were exposed to potentially inappropriate drug pairs 

experienced eight potentially inappropriate drug pairs, of which 

six were drug-drug interactions. 

For both SNP and other MA-PD beneficiaries, the majority of potential 

drug-drug interactions were of moderate risk 

Overall, 83 percent of potential drug-drug interactions were of moderate 

risk. In other words, five of the six potential drug-drug interactions, on 

average, were of moderate risk for beneficiaries who experienced 

potential drug-drug interactions. Eighty-four percent of potential 

drug-drug interactions for SNP beneficiaries and 83 percent for other 

MA-PD beneficiaries were of moderate risk. 

Moderate drug-drug interactions may cause some risk to the 

beneficiary. The moderate drug-drug interactions identified in this 

report could have led to problems such as low blood pressure, nausea, 

fatigue, or muscle weakness. 

Severe and serious interactions accounted for 17 percent of potential 

drug-drug interactions. Severe interactions, which result from two drugs 

that are contraindicated and should not usually be taken together, 

accounted for 1 percent of potential drug-drug interactions for both SNP 

and other MA-PD beneficiaries. Serious interactions, which may cause 

very harmful effects, accounted for 16 percent of all potential drug-drug 

interactions. Serious drug-drug interactions accounted for 15 percent of 

potential drug-drug interactions for SNP beneficiaries and 16 percent 

for other MA-PD beneficiaries. On average, one of the six potential 

drug-drug interactions for beneficiaries exposed to potentially 

inappropriate drug pairs was of either severe or serious risk. 

Severe and serious drug-drug interactions may require a change in drug 

regimen or monitoring by a health care professional. These interactions 

can lead to problems such as gastrointestinal damage, abnormal heart 

rates, or bleeding complications. 

Certain drugs were more likely to be involved in severe or serious 

potential drug-drug interactions. These drugs treat a variety of 

ailments, such as heart conditions, high blood pressure, blood clots, 

overactive bladders, infections, pain, high cholesterol, gastrointestinal 

disorders, and low potassium. See Appendix C for a list of the 20 drugs 

most frequently involved in severe or serious potential drug-drug 

interactions. 

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FINDINGS 

Two drugs, potassium chloride and warfarin sodium, stand out because 

of the frequency with which they were involved in either a severe or 

serious potential drug-drug interaction. Health care professionals are 

generally aware of both drugs’ potential risks and may have provided 

increased observation of beneficiaries taking these drugs. 

Potassium chloride was involved in 34 percent of severe potential 

drug-drug interactions. Potassium chloride can produce ulcerative 

lesions of the gastrointestinal tract.45 Some of the severe potential 

drug-drug interactions in which it was involved could have also 

produced gastrointestinal damage. Two of the drugs most frequently 

involved in potential drug-drug interactions with potassium chloride 

were lisinopril and spironolactone. These drugs are often prescribed in 

combination with potassium chloride but may require a decrease in the 

dose of potassium chloride and monitoring by a health care professional. 

Warfarin sodium was involved in 17 percent of serious potential 

drug-drug interactions. Warfarin sodium can increase the risk of 

hemorrhage.46 Some of the serious potential drug-drug interactions in 

which it was involved could have produced bleeding complications. 

Two of the drugs most frequently involved in potential drug-drug 

interactions with warfarin sodium were lovastatin and levothyroxine 

sodium. These drugs are often prescribed in combination with warfarin 

sodium but may require a decrease in the dose of warfarin sodium and 

monitoring by a health care professional. 

For both SNP and other MA-PD beneficiaries, the majority of potentially 

inappropriate drug pairs recurred 

Overall, 74 percent of all potentially inappropriate drug pairs recurred. 

Of these recurring potentially inappropriate drug pairs, 26 percent were 

produced by unique drug pairs; the rest were recurrences of these 

unique drug pairs. Seventy-seven percent of all potentially 

inappropriate drug pairs recurred for SNP beneficiaries and 74 percent 

recurred for other MA-PD beneficiaries. 

Seventy-nine percent of all severe and 80 percent of all serious potential 

drug-drug interactions were recurring errors. Twenty-three percent of 

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45 “Potassium Chloride.” Physicians’ Desk Reference, 60th ed., 2006, pp. 3047–3048. 

46 “Coumadin (Warfarin Sodium).” Physicians’ Desk Reference, 60th ed., 2006, 

pp. 932–937. 

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FINDINGS 

both the severe and serious potential drug-drug interactions that 

recurred were produced by unique drug pairs. 

The fact that most potentially inappropriate drug pairs recurred 

suggests that either the risks of the potential therapeutic duplications 

and drug-drug interactions were known and outweighed by medical 

necessity or that the physician or pharmacy was unaware of the risks. 

In some cases, health professionals may have been monitoring 

beneficiaries for potentially dangerous effects. In other cases, 

beneficiaries may have been repeatedly exposed to potential therapeutic 

duplications and drug-drug interactions, some of a severe or serious 

nature, that should have been detected and corrected. 

For both SNP and other MA-PD beneficiaries, the majority of 

potentially inappropriate drug pairs involved drugs prescribed by the 

same physician and filled by the same pharmacy

Overall, 66 percent of all potentially inappropriate drug pairs involved 

drugs prescribed by the same physician and dispensed by the same 

pharmacy. Twenty-two percent of all potentially inappropriate drug 

pairs were filled at the same pharmacy on the same day. 

Seventy-three percent of all potentially inappropriate drug pairs 

involved drugs that were prescribed by the same physician. In some of 

these cases, the physician may have been unaware of the potential risks 

of prescribing the two drugs together. One study of physicians’ 

knowledge of drug-drug interactions showed that they could correctly 

classify drugs as adversely interacting only about half of the time.47

Moreover, 88 percent of all potentially inappropriate drug pairs involved 

drugs that were filled by the same pharmacy. Pharmacies typically 

have concurrent drug utilization review systems that alert pharmacists 

to potentially inappropriate drug pairs. However, one study found that 

pharmacists override the majority of alerts, concluding that the high 

volume of alerts may be overwhelming.48 Another study found that 

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47 Peter A. Glassman, et al., 2002. “Improving recognition of drug interactions: benefits 

and barriers to using automated drug alerts.” Medical Care, vol. 40, pp. 1161–1171. 

48 Michelle A. Chui and Michael T. Rupp, 2006. “Evaluation of online prospective DUR 

programs in community pharmacy practice.” Journal of Managed Care Pharmacy, 

vol. 6, pp. 27–32. 

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FINDINGS 

pharmacists also may not always be aware of the potential risks of 

two drugs when taken together.49 

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49 Rich A. Weideman, et al., 1999. “Pharmacist recognition of potential drug 

interactions.” American Journal of Health System Pharmacy, vol. 56, pp. 1524–1529. 

P LAN BENEFICIARIES
 

ΔR FINDINGS RECOMMENDATIONS ECOMMENDATIONS RECOMMENDATION 

SNP beneficiaries filled more prescriptions and had higher average 

prescription drug costs than other MA-PD beneficiaries. This indicates 

that SNP beneficiaries may be different from other MA-PD 

beneficiaries, at least as far as their drug utilization and costs are 

concerned. In addition, although SNP beneficiaries had higher drug 

utilization than other MA-PD beneficiaries on average, SNP and other 

MA-PD beneficiaries were similarly exposed to potentially inappropriate 

drug pairs. At higher levels of drug utilization, SNP beneficiaries were 

less likely to be exposed to a potentially inappropriate drug pair than 

other MA-PD beneficiaries. 

SNP beneficiaries filled more prescriptions and had higher average 

prescription drug costs than other MA-PD beneficiaries. This indicates 

that SNP beneficiaries may be different from other MA-PD 

beneficiaries, at least as far as their drug utilization and costs are 

concerned. In addition, although SNP beneficiaries had higher drug 

utilization than other MA-PD beneficiaries on average, SNP and other 

MA-PD beneficiaries were similarly exposed to potentially inappropriate 

drug pairs. At higher levels of drug utilization, SNP beneficiaries were 

less likely to be exposed to a potentially inappropriate drug pair than 

other MA-PD beneficiaries. 

Regardless of whether beneficiaries were enrolled in a SNP or other 

MA-PD, the type and severity of their potentially inappropriate drug 

pairs were similar. Although most of the potential drug-drug 

interactions were of moderate risk, 17 percent posed severe or serious 

risk. Thus, in some cases beneficiaries may have been needlessly 

exposed to serious risk, with some potentially leading to an ADE. 

Therefore we make the following recommendation: 

Regardless of whether beneficiaries were enrolled in a SNP or other 

MA-PD, the type and severity of their potentially inappropriate drug 

pairs were similar. Although most of the potential drug-drug 

interactions were of moderate risk, 17 percent posed severe or serious 

risk. Thus, in some cases beneficiaries may have been needlessly 

exposed to serious risk, with some potentially leading to an ADE. 

Therefore we make the following recommendation: 

CMS Should Help SNPs and Other MA-PDs Provide Physicians and 

Pharmacists the Information They Need To Prevent Inappropriate Drug Pairs 

Leading to ADEs 

For SNP and other MA-PD beneficiaries, 66 percent of potentially 

inappropriate drug pairs involved drugs that were prescribed by the 

same physician and filled by the same pharmacy. Although some of the 

potentially inappropriate drug pairs could have been intentionally 

prescribed because medical professionals judged that the benefits 

outweighed the risks, others could have been errors. Thus, if physicians 

and pharmacists had been given the right information, some of these 

potentially inappropriate drug pairs could have been avoided. 

For SNP and other MA-PD beneficiaries, 66 percent of potentially 

inappropriate drug pairs involved drugs that were prescribed by the 

same physician and filled by the same pharmacy. Although some of the 

potentially inappropriate drug pairs could have been intentionally 

prescribed because medical professionals judged that the benefits 

outweighed the risks, others could have been errors. Thus, if physicians 

and pharmacists had been given the right information, some of these 

potentially inappropriate drug pairs could have been avoided. 

CMS should encourage plans to fully implement e-prescribing programs 

as one approach with the potential to help physicians and pharmacists 

screen for and prevent ADEs. E-prescribing can improve 

communication about beneficiaries’ medication histories, thus providing 

the information necessary to prevent ADEs. Standards for e-prescribing 

under Part D include a standard for allowing physicians, pharmacists, 

and Part D plans (which include SNPs and other MA-PDs) to 

communicate about beneficiaries’ medication histories, including 

information that may help identify ADEs. 

CMS should encourage plans to fully implement e-prescribing programs 

as one approach with the potential to help physicians and pharmacists 

screen for and prevent ADEs. E-prescribing can improve 

communication about beneficiaries’ medication histories, thus providing 

the information necessary to prevent ADEs. Standards for e-prescribing 

under Part D include a standard for allowing physicians, pharmacists, 

and Part D plans (which include SNPs and other MA-PDs) to 

communicate about beneficiaries’ medication histories, including 

information that may help identify ADEs. 

In addition, CMS should ask FDA, as part of its Sentinel Initiative, to 

develop a list of drug combinations that are likely to be involved in 

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RECOMMENDATION 

severe or serious ADEs for the Medicare population. Once FDA has 

compiled this list, CMS should distribute this targeted list of drug 

combinations to SNPs and other MA-PDs to help screen for potentially 

inappropriate drug pairs. As previously mentioned, one study found 

that concurrent drug utilization reviews may be flagging so many 

interactions that pharmacists find them more troublesome than helpful. 

A targeted list of potentially inappropriate drug pairs most likely to be 

involved in severe or serious ADEs could help SNPs and other MA-PDs 

target specific drugs and drug combinations to prevent ADEs. 

This list could also help SNPs and other MA-PDs better monitor 

beneficiaries at risk for an ADE. To this end, CMS could encourage 

plans to expand eligibility for MTM services to beneficiaries filling 

prescriptions for drugs on the list of drug combinations likely to be 

involved in severe or serious ADEs. 

Obtaining the information needed to prevent ADEs is a necessary first 

step, but it may not be sufficient. As mentioned earlier, providers can 

be overwhelmed by the amount of information they receive, rendering 

the information useless. To overcome this, CMS should encourage plans 

to provide tools to assist physicians and pharmacists in appropriately 

analyzing and using the information they receive. CMS could help 

plans provide educational material and/or training to physicians for 

identifying ADEs. 

AGENCY COMMENTS AND OFFICE OF INSPECTOR GENERAL 

RESPONSE 

CMS concurred with our recommendation to help SNPs and other 

MA-PDs provide physicians and pharmacists the information they need 

to prevent inappropriate drug pairs that could lead to ADEs. CMS 

noted that Part D sponsors are currently required to maintain systems 

to monitor drug utilization, including the use of potentially 

inappropriate drug pairs. 

In addition, CMS stated that it supports a number of efforts aimed at 

preventing inappropriate drug pairs that could lead to ADEs. In 

particular, CMS cited efforts to establish e-prescribing programs in 

Part D that provide prescription information and medication history to 

physicians and pharmacies. CMS is also collaborating with FDA on the 

Sentinel Project, which is designed to augment postmarketing 

surveillance of approved medical products to improve information on 

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RECOMMENDATION 

potential risks and drug-drug interactions. Finally, CMS is evaluating 

MTM best practices to assist MTM programs in meeting their statutory 

goal of optimizing therapeutic outcomes through improved use of Part D 

medications and reducing risk of adverse events. 

However, CMS expressed concern about our use of the First Databank 

drug product information database to identify potentially inappropriate 

drug pairs. CMS stated that First Databank algorithms have not been 

specifically validated for use in the Medicare population. Although this 

may be true, First DataBank is widely used by pharmacists, 

researchers, and health care plans, including the Department of 

Veterans Affairs, State Medicaid programs, and Part D sponsors, to 

identify inappropriate drug pairs. 

CMS suggested that any assessment of inappropriate drug pairs rely on 

information from FDA because there is no commercially available 

software that has been validated for this use in the Medicare 

population. We did not rely on information from FDA because FDA 

does not maintain drug information on potential risks and interactions 

in a format that would allow for a systematic assessment. Further, 

FDA has noted that there are barriers to inclusion of the elderly in 

clinical trials, leading us to believe that currently no complete and 

validated source of information specifically related to the Medicare 

population exists.50 Perhaps FDA’s Sentinel Project will help fill this 

gap. 

For the full text of CMS’s comments, see Appendix D. 

50 Michelle Meadows, “Medication Use and Older Adults.” FDA Consumer Magazine, 

July-August 2006. Available online at 

http://www.fda.gov/fdac/features/2006/406_olderadults.html. Accessed on November 14, 

2008. 
 

Δ APPENDIX~A 

Detailed Methodology 

This study analyzes Prescription Drug Event (PDE) data for Special 

Needs Plans (SNP) and other Medicare Advantage Prescription Drug 

plans (MA-PD). We did not analyze stand-alone prescription drug 

plans. 

Data Sources 

We used three data sources to conduct this study: (1) 2006 PDE data, 

(2) August 2007 First DataBank drug product information data, and 

(3) 2006 Centers for Medicare & Medicaid Services (CMS) plan-level 

descriptive data. 

CMS requires plans providing Part D drug coverage to submit PDE data 

for payment purposes. Each drug event included in these data 

represents the dispensing of a drug or medical supply for the injection of 

insulin. These data contain the beneficiary’s identification number, the 

Food and Drug Administration’s National Drug Code (NDC),51 the date 

of service, the number of days that the drug is supplied, the drug’s costs, 

the prescribing physician, and the pharmacy where the prescription was 

filled. Our analysis included final action PDE claims submitted by 

SNPs and other MA-PDs for 2006.52 

First DataBank is a database containing drug product information, such 

as drug name and therapeutic class, for each NDC. The August 2007 

First DataBank data contained information on all drugs covered by 

Part D in 2006, but with more up-to-date drug information than prior 

versions of the First DataBank data. 

First DataBank also includes a Duplicate Therapy Module and a 

Drug-Drug Interaction Module. The Duplicate Therapy Module 

provides information on whether two drugs from the same therapeutic 

class, when taken simultaneously, increase the risk of toxicity. The 

Drug-Drug Interaction Module identifies drug-drug interactions and 

their severity level. 

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23 

51 An NDC is a three-part universal identifier that specifies the drug manufacturer’s 

name, the drug form and strength, and the package size. 

52 Final action claims are those CMS uses to reconcile payments to plans. A PDE record 

is submitted each time a beneficiary fills a prescription covered under Part D. The PDE 

records may be amended or deleted up to 6 months after the end of the payment year. After 

that point, CMS considers them to be final action claims. 

P LAN BENEFICIARIES
 

APPENDIX A 

CMS publishes comprehensive plan-level data on all Part D plans that 

include contract and plan benefit package numbers, organization 

names, enrollment, and whether a plan is a SNP. 

Data Analysis 

The 2006 PDE data for SNPs and other MA-PDs include 6.4 million 

beneficiaries with 187 million prescriptions from 1,879 plans. We 

removed 137,000 prescriptions that were listed as partial fills because 

they create the possibility of misstating drug utilization, costs, and 

therapeutic duplications and drug-drug interactions. This removed 

from our analysis 1,134 beneficiaries who only partially filled 

prescriptions. 

Calculating prescription drug utilization and costs. We analyzed cost and 

utilization separately for each beneficiary and for each plan through 

which he or she filled a prescription. We then aggregated this 

information to represent the totals for SNP beneficiaries and other 

MA-PD beneficiaries. 

We counted prescriptions and costs according to the plan that paid for 

each prescription. To reflect utilization and costs, we used a weighted 

enrollment to compensate for beneficiaries who were enrolled in 

multiple plans during 2006. About 400,000 of the 6.4 million 

beneficiaries filled prescriptions from more than one plan. Of these, 

100,000 filled prescriptions from both a SNP and another MA-PD. 

We calculated weighted enrollment using prescription fill dates as a 

proxy for days of enrollment in plans. Beneficiaries with two plans were 

considered to be enrolled in Plan A from January 1 until midway 

between their last prescription in Plan A and their first prescription in 

Plan B. We calculated enrollment in Plan B from that midpoint until 

December 31. Enrollment for beneficiaries with more than two plans 

was calculated similarly using the first and last prescription fill dates 

for each plan. 

To be conservative, we assumed a full year of enrollment when 

weighting beneficiaries for our analysis. Assuming a full year of 

enrollment for all beneficiaries resulted in a larger enrollment figure 

than assuming partial-year enrollment, which led to lower, more 

conservative estimates of average utilization and cost. 

If a beneficiary was enrolled in multiple SNPs, enrollment weights for 

these plans were added together to form the beneficiary’s SNP 

enrollment weight. Enrollment weights for other MA-PDs were 

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P LAN BENEFICIARIES 24 
 

APPENDIX A 

similarly added together to form the beneficiary’s other MA-PD 

enrollment weights. The weights for each beneficiary equal one when 

summed. 

The weighting of beneficiaries resulted in a weighted enrollment of 

634,000 for SNPs and 5.8 million for other MA-PDs. We used these 

weighted enrollment figures to calculate average drug utilization and 

cost. 

Assessing the difference in SNP beneficiaries’ average annual prescription 

drug cost compared to that of other MA-PD beneficiaries. To determine 

potential explanations for differences between the average annual 

prescription drug cost per SNP beneficiary and that of other MA-PD 

beneficiaries, we analyzed prescription drug utilization and cost factors 

that might affect overall cost. 

To analyze prescription drug utilization, we compared the number of 

prescriptions filled by SNP beneficiaries to the prescriptions filled by 

other MA-PD beneficiaries. 

To analyze differences in cost, we compared the drug mix for SNP and 

other MA-PD beneficiaries to explore whether the difference in overall 

cost was related to SNP beneficiaries requiring more costly types of 

drugs. To do this, we compared the 40 drugs most dispensed to SNP 

beneficiaries to the 40 drugs most dispensed to other MA-PD 

beneficiaries. These drugs accounted for 46 percent of SNP 

beneficiaries’ drug utilization and 56 percent of other MA-PD 

beneficiaries’ drug utilization. 

To determine the cost of the drugs that differed between the two lists of 

most frequently dispensed drugs, we calculated an overall average 

prescription cost per drug. This was used as a proxy for the 

market-value of the drug. The overall average prescription drug cost 

was calculated by totaling the amount paid by both SNPs and other 

MA-PDs for each drug and dividing this by total utilization. 

We also determined whether SNP and other MA-PD beneficiaries 

utilized 30- and 90-day prescriptions differently, given that 90-day 

prescriptions are typically less expensive. We defined a 30-day 

prescription as any prescription with days of supply less than or equal 

to 44 days. We defined a 90-day prescription as any prescription with 

days of supply greater than 74 days. 

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APPENDIX A 

Finally, to assess drug prices paid by SNPs and other MA-PDs for the 

same drug, we compared the average prescription costs paid by plans 

for each drug. We did this for the 40 drugs most dispensed to SNP 

beneficiaries. We compared the prices SNPs paid for these top 40 drugs 

to the prices MA-PDs paid for the same drugs. We repeated these 

calculations for 30-day prescriptions and 90-day prescriptions, 

normalized to 30-day prescription costs. 

Calculating potential therapeutic duplications and drug-drug interactions. 

For our analysis of potential therapeutic duplications and drug-drug 

interactions, we did not include beneficiaries who filled prescriptions 

under more than one plan. We did this to avoid counting potential 

therapeutic duplications and drug-drug interactions involving drugs 

from two different plans. 

Beneficiaries who switch plans might also switch their physician or 

pharmacy to accommodate their new plan’s network. A new plan, 

pharmacy benefit management organization, pharmacy, or physician 

might not have medication histories for these beneficiaries. A greater 

number of potential therapeutic duplications and drug-drug interactions 

may result if a new physician is not aware of drugs a beneficiary is 

taking. Thus, the prevalence of potential therapeutic duplications and 

drug-drug interactions in this population is not comparable to the vast 

majority of beneficiaries who were enrolled in a single plan. 

Excluding these beneficiaries left 534,000 SNP beneficiaries and 

5.5 million other MA-PD beneficiaries in our analysis of potential 

therapeutic duplications and drug-drug interactions. We did not weight 

enrollment for our analysis of potential therapeutic duplications and 

drug-drug interactions because the beneficiaries in this analysis were 

enrolled only in one plan. 

We counted a potential therapeutic duplication when the following 

three criteria were met for a beneficiary: (1) two drugs were from the 

same therapeutic class, (2) the therapeutic class did not allow 

duplications according to First DataBank, and (3) the two drugs’ supply 

periods overlapped for at least 25 percent of the shortest of the supply 

periods. Because plans often limit beneficiaries’ ability to refill a 

prescription until the last 25 percent of the supply period, we used this 

criterion to reduce the possibility of including early refills in our count 

of potential therapeutic duplications. 

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APPENDIX A 

We counted a potential drug-drug interaction when the following 

two criteria were met for a beneficiary: (1) two drugs were flagged by 

First DataBank as interacting when taken simultaneously, and (2) the 

two drugs had supply periods that overlapped for at least 2 days. We 

used 2 days as the overlap period to avoid cases in which one 

prescription ended and the other began on the same day. We did not 

use the overlap period used for therapeutic duplications because there is 

not the same risk of inappropriately counting an early refill as a 

potential drug-drug interaction. 

To identify prescriptions that appeared to represent a drug change in 

response to the detection of a drug-drug interaction, we looked for 

potential therapeutic duplications that: (1) occurred within the fill 

period of a potential drug-drug interaction, (2) involved one drug in 

common with the potential drug-drug interaction, and (3) only occurred 

once. Further, we only considered cases in which the potential 

drug-drug interaction did not occur again after the therapeutic 

duplication. Over 190,000 therapeutic duplications appear to have been 

changes in medications to avoid potential drug-drug interactions. They 

represent 1 percent of all potential therapeutic duplications. Thus, the 

data contain some potential therapeutic duplications that may have 

been the result of a change in medication because of the detection of a 

drug-drug interaction. 

Assessing potential therapeutic duplications and drug-drug interactions. 

We analyzed exposure to potential therapeutic duplications and 

drug-drug interactions for each beneficiary. We then aggregated this 

information to represent totals for SNP beneficiaries and other MA-PD 

beneficiaries. 

We calculated the percentage of beneficiaries who had at least one 

potential therapeutic duplication or drug-drug interaction for different 

ranges in the number of prescriptions. We divided beneficiaries into 

these ranges based on their number of prescriptions. For each range of 

prescription drug utilization, we counted the number of beneficiaries 

with at least one potential therapeutic duplication or drug-drug 

interaction and divided it by the total number of beneficiaries in that 

range. 

To determine the average number of potential therapeutic duplications 

and drug-drug interactions among beneficiaries who were exposed to a 

potential therapeutic duplication or drug-drug interaction, we summed 

the number of potential therapeutic duplications and drug-drug 

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P LAN BENEFICIARIES 27 
 

APPENDIX A 

interactions for all beneficiaries and divided this by the number of 

beneficiaries exposed to a potential therapeutic duplication or drug-drug 

interaction. For potential drug-drug interactions, we repeated this 

calculation for each severity level defined by First DataBank. 

To find the top 20 drugs involved in severe and serious potential 

drug-drug interactions, we counted each occurrence of a unique drug in 

a severe and serious potential drug-drug interaction and found the 

drugs that were most frequently involved. 

To calculate the percentage of recurring potential therapeutic 

duplications and drug-drug interactions, we found the instances in 

which a beneficiary was exposed to potential therapeutic duplications 

and drug-drug interactions involving the same pair of drugs more than 

once during 2006. We divided the number of recurring drug pairs by 

the total number of potential therapeutic duplications and drug-drug 

interactions to find the percentage that recurred. Thus, if potential 

therapeutic duplications and drug-drug interactions from a particular 

drug combination occurred every month of the year, we counted that as 

12 recurring potential therapeutic duplications and drug-drug 

interactions. 

To calculate the percentage of unique drug pairs involved in recurring 

potential therapeutic duplications and drug-drug interactions, we first 

totaled the number of unique drug pairs involved in potential 

therapeutic duplications and drug-drug interactions. We then divided 

this by the total number of recurring potential therapeutic duplications 

and drug-drug interactions. We repeated this calculation for severe and 

serious potential drug-drug interactions. 

To determine how often two drugs involved in potential therapeutic 

duplications and drug-drug interactions were prescribed by the same 

physician or filled by the same pharmacy, we used the prescriber and 

provider identification numbers, respectively, provided in the PDE data. 

We then used the date of service to determine whether potential 

therapeutic duplications and drug-drug interactions were filled by the 

same pharmacy on the same day. 

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Differences in Cost for the Most Frequently Dispensed Prescription 

Drugs in Special Needs Plans

Table 2: Average Cost per 30-day, 90-day, and All Prescriptions for the 40 Drugs Most Frequently 

Dispensed to Special Needs Plan and Other Medicare Advantage Prescription Drug Plan* Beneficiaries

Average Cost per 30-Day 

Prescription 

Average Cost per 90-Day 

Prescription Normalized to 

30-Day Drug Supply 

Average Cost per 

Prescription Normalized to 

30-Day Drug Supply 

Drug Name SNPs Other MA-PDs SNPs Other MA-PDs SNPs Other MA-PDs 

Levothyroxine Sodium $8.31 $8.19 $6.60 $6.92 $8.22 $7.59 

Furosemide $2.46 $2.19 $2.23 $2.14 $2.45 $2.15 

Atorvastatin Calcium $89.40 $86.50 $85.52 $81.40 $89.18 $84.12 

Lisinopril $10.10 $9.59 $11.59 $8.49 $10.16 $9.00 

Metformin Hcl $16.42 $15.26 $19.40 $17.74 $16.50 $16.14 

Atenolol $3.71 $3.21 $4.41 $2.91 $3.73 $3.03 

Hydrochlorothiazide $2.58 $2.58 $2.26 $1.82 $2.56 $2.14 

Hydrocodone Bit/Acetaminophen $9.96 $10.13 $14.57 $13.55 $9.98 $10.25 

Amlodipine Besylate $54.34 $53.24 $51.97 $50.53 $54.22 $52.41 

Metoprolol Tartrate $3.93 $3.44 $4.17 $4.69 $3.93 $3.89 

Ranitidine Hcl $9.95 $8.61 $13.33 $9.74 $10.01 $8.89 

Potassium Chloride $11.49 $9.45 $8.69 $8.13 $11.36 $8.94 

Clopidogrel Bisulfate $118.21 $115.33 $105.78 $108.20 $117.66 $113.04 

Glipizide $11.72 $11.12 $11.08 $9.05 $11.68 $10.29 

Warfarin Sodium $11.88 $14.61 $12.65 $12.82 $11.90 $14.02 

Enalapril Maleate $10.20 $8.94 $11.56 $11.40 $10.23 $9.61 

Gabapentin $53.03 $45.94 $54.34 $54.57 $52.99 $48.10 

Lovastatin $34.18 $27.48 $30.91 $22.00 $33.83 $24.12 

Simvastatin $106.64 $106.49 $97.47 $85.05 $105.85 $95.87 

Alendronate Sodium $71.85 $70.35 $67.57 $60.67 $71.63 $65.30 

Source: Office of Inspector General analysis of 2006 Prescription Drug Event data, 2008.

Δ APPENDIX~B 

*Special Needs Plan = SNP 

 Medicare Advantage Prescription Drug Plan = MA-PD 

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APPENDIX B 

Table 2: Average Cost per 30-day, 90-day, and All Prescriptions for the 40 Drugs Most Frequently 

Dispensed to Special Needs Plan and Other Medicare Advantage Prescription Drug Plan Beneficiaries, 

continued

Average Cost per 30-Day 

Prescription 

Average Cost per 90-Day 

Prescription Normalized to 

30-Day Drug Supply 

Average Cost per 

Prescription Normalized to 

30-Day Drug Supply 

Drug Name SNPs Other MA-PDs SNPs Other MA-PDs SNPs Other MA-PDs 

Sertraline Hcl $79.70 $74.54 $69.40 $69.12 $79.41 $72.87 

Diltiazem Hcl $34.54 $34.75 $34.75 $31.52 $34.53 $33.46 

Digoxin $4.30 $4.33 $3.73 $4.03 $4.28 $4.19 

Quetiapine Fumarate $201.75 $149.47 $194.69 $146.53 $201.63 $148.47 

Albuterol $12.86 $11.33 $15.72 $12.96 $12.87 $11.34 

Pantoprazole Sodium $110.13 $109.18 $104.67 $104.33 $109.97 $107.89 

Isosorbide Mononitrate $10.46 $9.95 $12.68 $12.35 $10.53 $10.63 

Trazodone Hcl $5.13 $4.61 $7.93 $5.23 $5.18 $4.75 

Omeprazole $53.50 $39.65 $44.49 $31.06 $53.14 $34.88 

Risperidone $210.95 $166.17 $227.87 $180.75 $211.03 $167.49 

Metoprolol Succinate $32.18 $31.51 $30.14 $29.39 $31.99 $30.70 

Rosiglitazone Maleate $125.14 $123.57 $120.70 $118.62 $124.90 $122.04 

Oxycodone Hcl/Acetaminophen $19.15 $27.26 $28.57 $33.45 $19.16 $27.38 

Fluoxetine Hcl $16.92 $13.95 $20.34 $12.15 $16.99 $12.95 

Valsartan $58.23 $58.76 $56.17 $54.49 $58.15 $57.26 

Divalproex Sodium $136.67 $113.90 $149.34 $126.47 $136.79 $115.82 

Paroxetine Hcl $41.69 $35.92 $40.09 $31.34 $41.62 $34.14 

Glyburide $11.95 $12.09 $13.55 $12.83 $11.98 $12.32 

Ibuprofen $4.04 $3.99 $5.99 $5.53 $4.06 $4.21 

Nifedipine $48.03 $42.59 $43.60 $37.41 $47.80 $39.98 

Source: Office of Inspector General analysis of 2006 Prescription Drug Event data, 2008. 

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Drugs Most Frequently Involved in Severe and Serious Potential 

Drug-Drug Interactions 

Table 3: The 20 Drugs Most Frequently Involved in Severe and Serious Potential 

Drug-Drug Interactions 

Severe Serious

Drug Name

Primary 

Condition 

Treated 

Number of 

Severe 

Interactions Drug Name

Primary 

Condition 

Treated 

Number of 

Serious 

Interactions 

Potassium Chloride Low Potassium 

Levels 144,778 Warfarin Sodium Blood Clots 1,016,822 

Oxybutynin Overactive 

Bladder 50,429 Levothyroxine Sodium 

Low Thyroid 

Levels 385,271 

Tolterodine Tartrate Overactive 

Bladder 42,813 Potassium Chloride Low Potassium Levels 363,921 

Diphenoxylate 

Hcl/Atropine Sulfate Diarrhea 12,608 Clonidine Hcl High Blood 

Pressure 346,506 

Dicyclomine Hcl Functional GI 

Disorders 9,792 Gemfibrozil High Cholesterol 239,514 

Hyoscyamine Sulfate Functional GI 

Disorders 7,580 Ciprofloxacin Hcl Bacterial Infection 197,558 

Amiodarone Hcl Heart 

Arrhythmias 6,291 Amiodarone Hcl Heart Arrhythmias 194,097 

Selegiline Hcl Parkinson’s 

Disease 5,805 Triamterene/ Hydrochlorothiazide 

Low Potassium 

Levels 150,336 

Benztropine Mesylate Extrapyramidal 

Symptoms 5,308 Digoxin Congestive Heart Failure 144,990 

Solifenacin Succinate Overactive 

Bladder 4,492 Fenofibrate Nanocrystallized High Cholesterol 144,374 

Darifenacin 

Hydrobromide 

Overactive 

Bladder 4,310 Tramadol Hcl Pain 141,729 

Disopyramide 

Phosphate 

Heart 

Arrhythmias 3,698 Atorvastatin Calcium High Cholesterol 130,171 

Thioridazine Hcl Schizophrenia 2,722 Lovastatin High Cholesterol 119,036 

Ketoconazole Fungal Infection 2,366 Fluoxetine Hcl Depression 115,576 

Linezolid Bacterial 

Infection 1,957 Atenolol High Blood Pressure 111,713 

Ciprofloxacin Hcl Bacterial 

Infection 1,912 Metoprolol Tartrate High Blood Pressure 104,352 

Azithromycin Bacterial 

Infection 1,877 Sertraline Hcl Depression 100,254 

Trihexyphenidyl Hcl Parkinsonism 1,835 Spironolactone High Blood 

Pressure 98,114 

Fluoxetine Hcl Depression 1,794 Allopurinol Gout 97,857 

Ketorolac 

Tromethamine Pain 1,710 Levofloxacin Bacterial Infections 94,848 

Source: Office of Inspector General analysis of 2006 PDE data, 2008. 

Δ APPENDIX~C APPENDIX~C 

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P LAN BENEFICIARIES 31 
 

Δ APPENDIX ~ APPENDIX ~ A Δ APPENDIX ~ D D 

Agency Comments 

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P LAN BENEFICIARIES 32 
 

APPENDIX ~ D 

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P LAN BENEFICIARIES 33 
 

APPENDIX ~ D 

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P LAN BENEFICIARIES 34 
 

APPENDIX ~ D 

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P LAN BENEFICIARIES 35 
 

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P LAN BENEFICIARIES 36 

ΔAPPENDIX ~ D APPENDIX~B ACKNOWLEDGMENTS 

 

This report was prepared under the direction of Ann Maxwell, Regional 

Inspector General for Evaluation and Inspections in the Chicago 

regional office, and Thomas Komaniecki, Deputy Regional Inspector 

General. 

This report was led by Mark Stiglitz. Other principal Office of 

Evaluation and Inspections staff from the Chicago regional office who 

contributed include Meghan Kearns and Mara Werner; central office 

staff who contributed include Doris Jackson, Rita Wurm, and Robert 

Gibbons.