Department of Health and Human Services
OFFICE OF 
   
INSPECTOR GENERAL 
 
 
 
 
 
 
 
 
C S N
OMPARING  PECIAL  EEDS 
 
P B  O
LAN  ENEFICIARIES TO  THER 
 
M A
E DICARE  DVANTAGE 
 
P D P
RESCRIPTION  RUG  LAN 
 
 
B  
ENEFICIARIES
 
 
 
Daniel R. Levinson  
Inspector General 
 
December 2008 
OEI-05-07-00490   
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 OIGs 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. 
   
   
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 E X E C U T I V E   S U M M A R Y  
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, 
  OEI-05-07-00490  COMPARING SPECIAL NEEDS PLAN BENEFICIARIES TO OTHER MEDICARE ADVANTAGE PRESCRIPTION DRUG 
PLAN BENEFICIARIES  i   
   
E X E C U T I V E   S U M M A R Y  
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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E X E C U T I V E   S U M M A R Y  
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.   
  
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 T A B L E   O F   C O N T E N T S  
EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
 
 
I N T RO DUC T IO N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 
 
 
F I N D IN G S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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 
 
 
R E C O MMEN D A T ION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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 
 
A C K NO WL E D G M E N T S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 
   
   
 I N T R O D U C T I O N  
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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I N T R O D U C T I O N  
 
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 
 
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. 
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I N T R O D U C T I O N  
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 beneficiarys risk score, the higher the 
payment is for that beneficiary.  
 
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. 246247.  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). 
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I N T R O D U C T I O N  
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 
 
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. 
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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.  
 
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. 11071116. 
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.  
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Concurrent drug utilization review systems screen for potential drug 
therapy problems at a drugs 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 plans 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 
 
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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I N T R O D U C T I O N  
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.     
 
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. 
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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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CMSs 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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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 DataBanks 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 DataBanks 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 DataBanks severe, serious, and 
moderate severity levels. 
 
Table 1:  Severity Levels of Drug-Drug Interactions 
 
  Severity 
Level  Description of Interaction 
  These medicines are not usually taken together.  Contact health care 
Severe 
professional (e.g., doctor or pharmacist) for more information. 
  These medicines may interact and cause very harmful effects.  
Serious 
Contact health care professional for more information.  
 
These medicines may cause some risk when taken together.  
Moderate 
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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I N T R O D U C T I O N  
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 Presidents Council on Integrity and 
Efficiency and the Executive Council on Integrity and Efficiency. 
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 F I N D I N G S  
On average, SNP beneficiaries had higher  On average, SNP beneficiaries filled 
prescription drug utilization and costs than  11 percent more prescriptions and 
had 49 percent higher average 
other MA-PD beneficiaries 
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 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 
  OEI-05-07-00490  COMPARING SPECIAL NEEDS PLAN BENEFICIARIES TO OTHER MEDICARE ADVANTAGE PRESCRIPTION DRUG 
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F I N D I N G S  
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.   
 
  OEI-05-07-00490  COMPARING SPECIAL NEEDS PLAN BENEFICIARIES TO OTHER MEDICARE ADVANTAGE PRESCRIPTION DRUG 
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FFFF IIII NNNN DDDD IIII NNNN GGGG SSSS     
Because SNP beneficiaries filled 
Despite SNP beneficiaries higher rates of drug 
more prescriptions for more drugs 
utilization, SNP and other MA-PD beneficiaries 
than other MA-PD beneficiaries, 
were similarly exposed to potentially 
they might be expected to be at 
inappropriate drug pairs 
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.   
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.   
  OEI-05-07-00490  COMPARING SPECIAL NEEDS PLAN BENEFICIARIES TO OTHER MEDICARE ADVANTAGE PRESCRIPTION DRUG 
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F I N D I N G S  
Chart 1:  Percentage of SNP and Other MA-PD Beneficiaries Exposed to a Therapeutic 
Duplication or Drug-Drug Interaction for Ranges of Prescriptions 
100%
90%
80%
s 70%
e
ari
efici 60%
n
e
B SNPs
of  50% Other MA-PDs
e 
g
a
nt 40%
e
c
r
e
P 30%
20%
10%
0%
120 2140 4160 6180 81+
Number of Prescriptions During 2006
Source:  Office of Inspector General (OIG) analysis of 2006 PDE data, 2008. 
 
The majority of potentially inappropriate drug  The type and severity of the 
potentially inappropriate drug 
pairs were drug-drug interactions of moderate 
pairs SNP and other MA-PD 
risk for both SNP and other MA-PD beneficiaries 
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.     
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 
  OEI-05-07-00490  COMPARING SPECIAL NEEDS PLAN BENEFICIARIES TO OTHER MEDICARE ADVANTAGE PRESCRIPTION DRUG 
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FFFFFF IIIIII NNNNNN DDDDDD IIIIII NNNNNN GGGGGG SSSSSS       
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.  
  OEI-05-07-00490  COMPARING SPECIAL NEEDS PLAN BENEFICIARIES TO OTHER MEDICARE ADVANTAGE PRESCRIPTION DRUG 
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F I N D I N G S  
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 
 
45 Potassium Chloride.  Physicians Desk Reference, 60th ed., 2006, pp. 30473048.  
46 Coumadin (Warfarin Sodium).  Physicians Desk Reference, 60th  ed., 2006,  
pp. 932937.  
 
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F I N D I N G S  
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 
 
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. 11611171. 
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. 2732. 
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F I N D I N G S  
pharmacists also may not always be aware of the potential risks of 
two drugs when taken together.49   
 
49 Rich A. Weideman, et al., 1999.  Pharmacist recognition of potential drug 
interactions.  American Journal of Health System Pharmacy, vol. 56, pp. 15241529. 
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aanndd  pphhaarrmmaacciissttss  hhaadd  bbeeeenn  ggiivveenn  tthhee  rriigghhtt  iinnffoorrmmaattiioonn,,  ssoommee  ooff  tthheessee  
ppootteennttiiaallllyy  iinnaapppprroopprriiaattee  ddrruugg  ppaaiirrss  ccoouulldd  hhaavvee  bbeeeenn  aavvooiiddeedd..      
CCMMSS  sshhoouulldd  eennccoouurraaggee  ppllaannss  ttoo  ffuullllyy  iimmpplleemmeenntt  ee--pprreessccrriibbiinngg  pprrooggrraammss  
aass  oonnee  aapppprrooaacchh  wwiitthh  tthhee  ppootteennttiiaall  ttoo  hheellpp  pphhyyssiicciiaannss  aanndd  pphhaarrmmaacciissttss  
ssccrreeeenn  ffoorr  aanndd  pprreevveenntt  AADDEEss..    EE--pprreessccrriibbiinngg  ccaann  iimmpprroovvee  
ccoommmmuunniiccaattiioonn  aabboouutt  bbeenneeffiicciiaarriieess  mmeeddiiccaattiioonn  hhiissttoorriieess,,  tthhuuss  pprroovviiddiinngg  
tthhee  iinnffoorrmmaattiioonn  nneecceessssaarryy  ttoo  pprreevveenntt  AADDEEss..    SSttaannddaarrddss  ffoorr  ee--pprreessccrriibbiinngg  
uunnddeerr  PPaarrtt  DD  iinncclluuddee  aa  ssttaannddaarrdd  ffoorr  aalllloowwiinngg  pphhyyssiicciiaannss,,  pphhaarrmmaacciissttss,,  
aanndd  PPaarrtt  DD  ppllaannss  ((wwhhiicchh  iinncclluuddee  SSNNPPss  aanndd  ootthheerr  MMAA--PPDDss))  ttoo  
ccoommmmuunniiccaattee  aabboouutt  bbeenneeffiicciiaarriieess  mmeeddiiccaattiioonn  hhiissttoorriieess,,  iinncclluuddiinngg  
iinnffoorrmmaattiioonn  tthhaatt  mmaayy  hheellpp  iiddeennttiiffyy  AADDEEss..      
IInn  aaddddiittiioonn,,  CCMMSS  sshhoouulldd  aasskk  FFDDAA,,  aass  ppaarrtt  ooff  iittss  SSeennttiinneell  IInniittiiaattiivvee,,  ttoo  
ddeevveelloopp  aa  lliisstt  ooff  ddrruugg  ccoommbbiinnaattiioonnss  tthhaatt  aarree  lliikkeellyy  ttoo  bbee  iinnvvoollvveedd  iinn  
  OEI-05-07-00490  COMPARING SPECIAL NEEDS PLAN BENEFICIARIES TO OTHER MEDICARE ADVANTAGE PRESCRIPTION DRUG 
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R E C O M M E N D A T I O N  
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 
  OEI-05-07-00490  COMPARING SPECIAL NEEDS PLAN BENEFICIARIES TO OTHER MEDICARE ADVANTAGE PRESCRIPTION DRUG 
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R E C O M M E N D A T I O N  
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 FDAs Sentinel Project will help fill this 
gap. 
For the full text of CMSs 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. 
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 A P P E N D I X ~ 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 beneficiarys identification number, the 
Food and Drug Administrations National Drug Code (NDC),51 the date 
of service, the number of days that the drug is supplied, the drugs 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. 
 
51 An NDC is a three-part universal identifier that specifies the drug manufacturers 
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.   
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A P P E N D I X   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 beneficiarys SNP 
enrollment weight.  Enrollment weights for other MA-PDs were 
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A P P E N D I X   A  
similarly added together to form the beneficiarys 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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A P P E N D I X   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 plans 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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A P P E N D I X   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 
  OEI-05-07-00490  COMPARING SPECIAL NEEDS PLAN BENEFICIARIES TO OTHER MEDICARE ADVANTAGE PRESCRIPTION DRUG 
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AAA PPP PPP EEE NNN DDD III XXX     AAA    
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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   A P P E N D I X ~ B  
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 90-Day  Average Cost per 
Average Cost per 30-Day  Prescription Normalized to  Prescription Normalized to 
Prescription  30-Day Drug Supply  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. 
*Special Needs Plan = SNP 
  Medicare Advantage Prescription Drug Plan = MA-PD 
 
 
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A P P E N D I X   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 90-Day  Average Cost per 
Average Cost per 30-Day  Prescription Normalized to  Prescription Normalized to 
Prescription  30-Day Drug Supply  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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 A  AP PP PE EN ND DI IX X~ ~C C   
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 
Number of  Number of 
Primary  Primary 
Severe  Serious 
Condition  Condition 
Interactions  Interactions 
Drug Name  Treated  Drug Name  Treated 
Low Potassium 
Potassium Chloride  144,778  Warfarin Sodium  Blood Clots  1,016,822 
Levels 
Overactive  Levothyroxine  Low Thyroid 
Oxybutynin   50,429  385,271 
Bladder  Sodium  Levels 
Overactive  Low Potassium 
Tolterodine Tartrate  42,813  Potassium Chloride  363,921 
Bladder  Levels 
Diphenoxylate  High Blood 
Diarrhea  12,608  Clonidine Hcl  346,506 
Hcl/Atropine Sulfate  Pressure 
Functional GI 
Dicyclomine Hcl  9,792  Gemfibrozil  High Cholesterol  239,514 
Disorders 
Functional GI  Bacterial 
Hyoscyamine Sulfate  7,580  Ciprofloxacin Hcl  197,558 
Disorders  Infection 
Heart  Heart 
Amiodarone Hcl  6,291  Amiodarone Hcl  194,097 
Arrhythmias  Arrhythmias 
  Parkinsons  Triamterene/  Low Potassium 
Selegiline Hcl 5,805  150,336 
Disease  Hydrochlorothiazide  Levels 
Extrapyramidal  Congestive 
Benztropine Mesylate  5,308  Digoxin  144,990 
Symptoms  Heart Failure 
Overactive  Fenofibrate 
Solifenacin Succinate  4,492  High Cholesterol  144,374 
Bladder  Nanocrystallized 
Darifenacin  Overactive 
4,310  Tramadol Hcl  Pain  141,729 
Hydrobromide  Bladder 
Disopyramide  Heart 
3,698  Atorvastatin Calcium  High Cholesterol  130,171 
Phosphate  Arrhythmias 
Thioridazine Hcl  Schizophrenia  2,722  Lovastatin  High Cholesterol  119,036 
Ketoconazole  Fungal Infection  2,366  Fluoxetine Hcl  Depression  115,576 
Bacterial  High Blood 
Linezolid  1,957  Atenolol  111,713 
Infection  Pressure 
Bacterial  High Blood 
Ciprofloxacin Hcl  1,912  Metoprolol Tartrate  104,352 
Infection  Pressure 
Bacterial 
Azithromycin  1,877  Sertraline Hcl  Depression  100,254 
Infection 
High Blood 
Trihexyphenidyl Hcl  Parkinsonism  1,835  Spironolactone  98,114 
Pressure 
Fluoxetine Hcl  Depression  1,794  Allopurinol  Gout  97,857 
Ketorolac  Bacterial 
Pain  1,710  Levofloxacin  94,848 
Tromethamine  Infections 
Source:   Office of Inspector General analysis of 2006 PDE data, 2008. 
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Agency Comments 
 
 
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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. 
 
 
 
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