There is fairly rich evidence that details challenges associated with medication use and application of CDS in specific improvement opportunities. Journals such as those in general internal medicine , medical informatics , and other disciplines are increasingly devoting theme issues and other coverage to such topics. A comprehensive literature review is beyond this guide’s scope, but a sampling helps set the stage for the guidance that follows.
Medication errors, which indicate breakdown in the medication use cycle and may cause bad outcomes, are increasingly the focus of public attention and local and national improvement efforts. A recent report from the IOM highlights the challenges and opportunities.
In 2006, IOM released a landmark report on medication safety entitled Preventing Medication Errors, as part of their Quality Chasm series.  The report looked at both prescribing and administration errors. Prescribing error rates ranged from 12.3 to 1,400 errors per 1,000 admissions. The wide distribution reflects varying methods for finding errors—estimates at the lower end were generally based on error reports filed by clinicians. The study that estimated the error rate at 1,400 errors per 1,000 admissions was based on chart review and estimated approximately 0.3 errors per patient per day.  Although most of these errors were unlikely to result in patient harm, 7.5% of them either resulted in a preventable ADE or could have resulted in one.
Administration errors also occur with significant frequency. The IOM report reviewed five studies that estimated administration error rates as between 2.4 and 11.1 errors per 100 medication administrations. The IOM committee estimated that between all sources of errors, a hospital patient is subject, on average, to one medication error per day.
The IOM report also synthesized research on medication errors in the outpatient setting, citing studies which found that 21% of all prescriptions contain at least one error , 3% of doses in an outpatient chemotherapy unit contained an error , and between 1.7% and 24% of community pharmacy prescriptions were dispensed incorrectly. 
Beyond error incidence, the IOM report also reviewed research on the incidence of ADEs. They found three studies that met their inclusion criteria. These studies estimated the preventable ADE rate at 1.2 preventable ADEs per 100 admissions , 1.8 preventable ADEs per 100 non-obstetric admissions , and 5.57 ADEs per 1,000 patient days.  Preventable ADEs in hospitalized patients increased length of stay (LOS) by 4.6 days and total costs by $5857 (1993 cost data).  In ambulatory Medicare patients at least 65 years old, the cost (in 2000 dollars) per preventable ADE is estimated at $1983. 
Based on this literature synthesis, the IOM report concludes that, in the United States, 1.5 million people suffer preventable injury every year as a result of medication errors. Roughly 530,000 preventable drug-related injuries occur each year among Medicare recipients in outpatient clinics alone. The extra annual medical costs for treating patient injuries that occur in hospitals alone is $3.5 billion.
"The Future Is Already Here, It’s Just Unevenly Distributed" 
As outlined previously in this chapter, CDS holds great promise for addressing the pressing challenges related to medication use that have been identified by IOM and others. A growing collection of studies demonstrates that this promise is currently being realized in leading organizations to varying degrees. In developing this guidebook, an effort has been made to base implementation recommendations on evidence from such literature on successful practices; therefore references are included throughout. Given the practical focus and largely volunteer nature of this effort, the literature analysis has been more opportunistic than exhaustive.
Perhaps a more important barrier to providing strongly evidence-based implementation guidance than extensive literature review is that, although there have been a number of studies on medication-related CDS, this literature only covers, and in a somewhat limited manner, the full medication management cycle. Even in relatively well-studied areas, such as CPOE to reduce ADEs, major gaps still exist.  Further, much of the published literature is derived from leading academic organizations with locally developed systems; 70% of the studies in this review examining ADE rates used homegrown CPOE with CDS. 
There is much to be learned from these pioneers, but the CDS functionality and results from custom-crafted systems in academic settings may not be directly transferred elsewhere. In this guide, we have tried to extrapolate lessons from groundbreaking efforts to healthcare delivery settings in which vendor supplied systems are the norm and organizational dynamics may be different. Where evidence is not specifically cited, the guidance provided is drawn from the experience of the editors, contributors, and reviewers, based on success strategies (or at least thoughtful approaches) gleaned in the course of their efforts.
In subsequent chapters, we occasionally reference CDS studies to reinforce specific recommendations. For example, Chapter 5 contains references to studies exploring the issues in applying CDS to various specific targets, such as reducing drug-allergy, DDI, and drug dosing problems. In addition, the following is a sampling from the literature on applying CDS to medication management. Studies of this sort have been loosely summarized in various sources such as the "Roadmap for National Action on CDS,"  the IOM report, "Preventing Medication Errors,"  and systematic reviews of CPOE with CDS as previously mentioned. 
Sampling of Literature on CDS in Medication Management
- Utilizing CDS has been shown to improve adherence to guidelines. Traditionally, clinical guidelines are left "on the shelf" and, as a result, errors and suboptimal care persist. Using CDS to communicate the guidance within clinician workflow, and hence increase adherence, has resulted in an absolute increase in influenza and pneumococcal vaccination of 12% and 20%, respectively.  Another study demonstrated a 3.3% absolute decrease in the primary endpoint of DVT or PE within 90 days after hospitalization. 
- CPOE with CDS has improved physician prescribing practices, formulary adherence, and cost savings , and produced an 86% absolute reduction in non-intercepted serious medication errors. 
- CDS for empiric preoperative antibiotic selection decreased postoperative wound infections. 
- CDS-supported medication dosing produced a 21% increase in appropriate medication prescribing in renal insufficiency and a 4.5% reduction in length of stay (LOS). 
- EMR use does not appear to be associated with improved performance on ambulatory care quality indicators without focused CDS features  and basic computer prescribing (which improves legibility and completeness) was not associated with a reduced rate of errors in an outpatient setting unless combined with advanced systems with CDS (drug-drug, drug allergy, and drug-interaction checking).  Similarly, even hospitals with highly computerized medication management processes experience high rates of ADEs without CDS focused specifically on drug selection, dosing and monitoring.  To realize benefits of CDS within CPOE, authors have suggested a two-stage approach: (1) basic CDS (drug-allergy testing, basic dosing guidance, duplication checking, and DDI checking); followed by (2) advanced CDS (dose-lab, renal dosing, drug-disease checking). 
- A systematic review found that CPOE reduces medication errors and ADEs.  Extensive tables featured in this review outline the CDS functionality examined in various studies, whether the systems were homegrown or commercial, and the risk ratio for ADEs with the system.
We will take a closer look at literature-suggested CDS targets in Chapter 2.