Data Tracking in Antimicrobial Stewardship Programs

November 2012 - Vol.9 No. 11 - Page #34

Implementing an evidence-based antimicrobial stewardship program (ASP) is an effective means of optimizing antibiotic prescribing and ensuring judicious antimicrobial use, thus improving patient outcomes. Such a program is also the cornerstone in efforts to reduce the threatening spread of antimicrobial resistance. Adopting a policy and procedure, initiating a medical surveillance program, performing staff education, and accurately tracking antibiotic use are required elements of a successful antimicrobial stewardship program. However, capturing and tracking drug use data can be a particularly challenging pursuit for many health systems.

TriStar Centennial Medical Center (TriStar CMC) is a community-based, non-teaching, tertiary care facility with 657 licensed beds, including a 25-bed hematology/bone marrow transplant unit, a 132-bed psychiatric facility, and 81 critical care beds. The facility is the flagship hospital of the Healthcare Corporation of America (HCA), a large, for-profit health care system. The pharmacy department at TriStar CMC consists of 41 pharmacist FTEs. It follows a decentralized clinical model, with clinical pharmacists performing medication therapy review on all patients admitted to the medical center. Among the clinical specialists is a pharmacist specializing in infectious diseases (IDs), who is in charge of the ASP for the facility. The central goals of the hospital’s ASP include establishing effective policies and guidelines, increasing data access through robust drug use monitoring, and auditing processes to improve antimicrobial stewardship initiatives.

The Antimicrobial Management Program
Although a recent HCA initiative brought antimicrobial stewardship to the forefront, the position of ID pharmacist has been in place at TriStar CMC for more than seven years. The ID pharmacist plays a leadership role in the ASP; in addition, two ID physicians, a clinical microbiologist, three infection preventionists, clinical pharmacy staff, and hospital administrators provide support for the ASP and its initiatives.

The ASP program was developed using the guidelines of the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA).1 Since the program’s inception, notable initiatives have included:

  • Pharmacist-driven intravenous-to-oral and renal dosing policies
  • Pharmacist-driven pharmacokinetic monitoring of vancomycin and aminoglycosides
  • Antimicrobial automatic stop orders
  • Formulary preauthorization requirements
  • A daily prospective audit with intervention and feedback

Formulary preauthorization is vital to the day-to-day functioning of the ASP, and requires an ID physician to approve certain high-cost or high-risk anti-infective agents, including daptomycin, linezolid, and tigecycline. The prospective audit with intervention and feedback is also key to daily operations. The ID pharmacist, with assistance from the decentralized pharmacists, reviews reports from the hospital pharmacy order entry system, daily labs, microbiology reports, and data from patient charts to identify potential opportunities for intervention. The ID pharmacist makes recommendations by issuing a pharmacy recommendation form, sending a text to the provider’s pager, or speaking with the provider or the respective nurse.

In addition to these daily tasks, the ID pharmacist has a number of longitudinal responsibilities. Among them is tracking data on program performance, as well as antimicrobial utilization, resistance rates, and costs. Tracking these data and those from other process and outcome measures can help an ASP illustrate its impact, as well as identify new opportunities for investigation and improvement.

Antimicrobial Acquisition Cost
Since antimicrobial medications constitute a large portion of hospital drug budgets, a secondary goal of many ASPs is to reduce antimicrobial expenditures without negatively affecting quality of care. Monitoring and reporting antimicrobial spending helps ASPs demonstrate their value from an economic standpoint. One approach to measurement is to normalize antimicrobial costs to a specific number of patient-days, while another is to monitor total antimicrobial spending over a specific time. At one large academic medical center, implementation of an ASP led to an estimated average annual savings of $920,000 to $2 million over 11 years. Even after accounting for the salaries of the individuals involved in the ASP, overall savings were significant.3

The largest reduction in antimicrobialexpenditures tends to occur early in an ASP’s existence when the program targets low-hanging fruit. After this, large decreases in spending are less likely.4 Also, the ASP, as well as hospital administration, need to consider other factors that can impact costs beyond the ASP’s control. These include inflation, availability of new generic antimicrobials, approval of new brand-name medications, and changes in local or national guidelines favoring higher-cost medications.3,4 Adjusting for some or all of these factors is necessary for comparisons of yearly expenditures to yield accurate conclusions, particularly later on in an ASP’s existence. Our drug costs are monitored at division and corporate levels, with the understanding that such factors may affect expenditure trends, both positively and negatively.

One factor that using antibiotic acquisition cost as an outcome measure does not take into account is the beneficial impact an ASP can have on non-drug expenditures, such as those associated with choosing an appropriate empiric antibiotic, even if it is a more expensive agent.3 Also, tracking antibiotic acquisition cost has limitations as a metric for antibiotic utilization. Doses that are wasted or otherwise not administered may be included in antibiotic spending reports, leading to an inaccurate representation of what is actually administered to a hospital’s patients over a given time. A number of other metrics can be used to monitor antimicrobial use.1

Antimicrobial Utilization Metrics
The IDSA/SHEA guidelines recommend that ASPs identify metrics to monitor antimicrobial utilization in order to demonstrate the program’s impact.1 Such metrics also can help an ASP compare its use of antimicrobials to that of similar hospitals, monitor trends in antimicrobial usage, and identify outliers for further investigation through medication use evaluations (MUEs).

Defined Daily Dose Metric
IDSA/SHEA guidelines do not recommend a specific metric for all circumstances. They do state that the defined daily dose (DDD) is useful for similar hospitals to compare antimicrobial use. The DDD is the assumed average maintenance dose per day for a drug used for its main indication in adults. This statistic is promoted by the World Health Organization (WHO); a searchable list of DDDs is available on the WHO Web site ( Calculating the number of DDDs of a drug involves adding the weight of the drug administered to a hospital’s patients over a given period, then dividing the total by its WHO-defined DDD. The result can be normalized by converting it to DDD per 100 or 1000 patient days.

In some European countries, hospitals are required to report antimicrobial consumption using DDD,6 but this is not the case in the US. Still, DDD is commonly used to monitor and compare antimicrobial use among hospitals, and benchmarks were reported in 2004 by the Centers for Disease Control and Prevention’s (CDC) National Nosocomial Infections Surveillance (NNIS) System.7

Our facility monitors DDD per 1000 patient days for the whole hospital on a monthly basis. Results are reported to the pharmacy department, the infection prevention committee, and HCA corporate. DDD also is measured quarterly for areas of high utilization, such as the intensive care units and the hematology/bone marrow transplant unit. This practice has allowed TriStar CMC to identify potential MUEs and further investigate changes in use in particular areas.

Limitations of the Defined Daily Dose Metric
While DDD is a valuable metric, it has significant limitations.5,8,9 One is that DDD does not always reflect a drug’s prescribed daily dose.6 This can limit an ASP’s ability to make accurate comparisons between antimicrobial classes or with other hospitals. It can also lead to an inaccurate assessment of the number of days the drug was used.9 For example, the DDD for meropenem is 2 grams.5 At TriStar CMC, the typical prescribed daily dose for a patient with normal renal function is meropenem 500 mg administered every six hours; therefore, one DDD reflects one day of therapy for many patients. At another hospital, the normal daily prescribed dose for a patient with normal renal function might be 1 gram administered every eight hours. In this hospital, DDD may overestimate carbapenem exposure. These two hospitals’ use of carbapenem use cannot be accurately compared, as a similar number of days of therapy would result in a higher number of DDDs in the second hospital. A similar discordance occurs with cefepime, which has a DDD of 2 grams.5 At TriStar CMC, the daily prescribed cefepime dose for many indications is 4 grams; in some cases it is 6 grams. As a result, it is possible that the DDD will overestimate days of cefepime use, and thus, an accurate comparison with other antipseudomonals cannot be made.

A similar limitation of the DDD metric is that it may overestimate or underestimate antibiotic exposure in patients with certain comorbidities or disease states. If a hospital has a patient population with a high rate of renal dysfunction, the DDDs of antimicrobials requiring renal dose adjustments might be regularly underestimated.9 Overestimation of usage can occur when a hospital has a large patient population with a disease state requiring higher daily doses of a particular antimicrobial, such as cefepime for neutropenic fever.10 Similarly, an antimicrobial that is dosed on weight, such as daptomycin, may have a wide range of prescribed daily doses.

Finally, the DDD methodology does not apply to pediatric patients according to the WHO definition.5 This not only means that the DDD metric cannot be used to monitor antimicrobial utilization in this population, but also that if an ASP’s antimicrobial administration report includes drug administered to pediatric patients, DDD results may be inaccurate.9

The Days-On-Therapy Metric
The days-on-therapy (DOT) metric potentially overcomes the limitations posed by the DDD methodology by avoiding underestimations and overestimations of antimicrobial usage and being applicable to pediatric populations.9 The IDSA/SHEA guidelines on antimicrobial stewardship report DOT as a potentially more accurate measurement for antimicrobials requiring renal dose adjustment because DOT reflects the total days an antimicrobial was administered, regardless of dose.1 The major disadvantage is that DOT can be more difficult to measure, particularly without appropriate computerized records. Perhaps not surprisingly, it has been shown that DDD and DOT methods provide significantly different results for a number of antimicrobials.9

The difficulty of obtaining patient-level data prevents some institutions, including TriStar CMC, from being able to implement DOT methodology. Still, it is becoming a more widely recommended, utilized, and studied metric. The CDC’s National Healthcare Safety Network, the successor to NNIS, measures antimicrobial consumption by DOT.11 Additionally, a multidisciplinary panel recently recommended DOT—and not DDD—as a quality metric to implement internally and use for external public reporting.4 Benchmarks for DOT per 1000 patient days also have been identified for a variety of clinical categories through an evaluation of antimicrobial use across 70 US academic medical centers.12 This report also describes the length-of-therapy metric, a measurement of days that any antimicrobial is used. The length-of-therapy methodology can be used in combination with DOT to track combination antimicrobial use.12

Measuring Acceptance of ASP Recommendations 
At TriStar CMC, the ASP measures the acceptance of its antimicrobial recommendations as both the number of acceptances and the acceptance rate. (This is not a metric directly mentioned in the IDSA/SHEA guidelines.) To calculate the number of acceptances, the pharmacist making the intervention enters the recommendation into the pharmacy department’s intervention documentation system. The total is compiled monthly and reported to HCA corporate. Acceptance rates of antibiotic recommendations are calculated using the number of accepted and rejected interventions, and are reported monthly to pharmacy. Monthly rates are generally between 85% and 95%, though there is no official benchmark for purposes of comparison. Depending on the level of detail in an ASP’s documentation, it may be possible to identify acceptance rates for a particular provider group or type of antimicrobial recommendation. This could be helpful in identifying targets for additional education.

Antibiotic recommendations throughout the TriStar division of HCA are linked to both cost savings and cost avoidance. While not every recommendation actually saves or avoids the specified amount, the practice serves as a surrogate for measuring drug and overall health care cost savings. Recommendations help the ASP monitor its success and value to the hospital and may be used to support future program expansion.

Additional Metrics and Outcome Measures
Additional types of information can be monitored through the ASP, particularly with respect to outcomes. Along with DOT, it is recommended that ASPs monitor:

  • The number of patients with specific drug-resistant organisms (including Staphylococcus aureus, Clostridium difficile, and Pseudomonas aeruginosa)
  • Mortality related to antimicrobial-resistant organisms
  • Avoided unnecessary treatment days in patients with community-acquired pneumonia, skin or soft-tissue infection, sepsis, and bloodstream infections
  • Unplanned hospital readmission within 30 days of discharge in the same four patient groups4

At TriStar CMC, a yearly hospital-wide antibiogram is compiled, including rates of methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococci, and extended-spectrum beta-lactamase-producing organisms. Rates of C. difficile infection also are reported every other month to the infection prevention committee. These outcome measures can be used to identify targets for improvement, such as in the instance of a C. difficile infection outbreak, and reflect a program’s success.

As antimicrobial resistance is a growing problem worldwide, each health system must take part in reducing its growth through implementing effective ASPs. However, only 48% of US hospitals currently have such a program in place.13 Curbing inappropriate antimicrobial use is vital to defending against the spread of drug-resistant pathogens, and pharmacy must take a lead role in implementing and promoting an effective ASP.


  1. Dellit TH, Owens RC, McGowan JE Jr, et al. Infectious Diseases Society of America and the Society for Healthcare Epidemiology of America guidelines for developing an institutional program to enhance antimicrobial stewardship. Clin Infect Dis. 2007;44(2):159-177.
  2. John JF Jr, Fishman NO. Programmatic role of the infectious diseases physician in controlling antimicrobial costs in the hospital. Clin Infect Dis. 1997;24(3):471-485.
  3. Beardsley JR, Williamson JC, Johnson JW, Luther VP, Wrenn RH, Ohl CC. Show me the money: long-term financial impact of an antimicrobial stewardship program. Infect Control Hosp Epidemiol. 2012;33(4):398-400.
  4. Morris AM, Brener S, Dresser L, et al. Use of a structured panel process to define quality metrics for antimicrobial stewardship programs. Infect Control Hosp Epidemiol. 2012;33(5):500-506.
  5. WHO Collaborating Centre for Drug Statistics Methodology. ATC/DDD index 2012. Oslo, 2011. Accessed June 27, 2012.
  6. Muller A, Monnet DL, Talon D, Henon T, Bertrand X. Discrepancies between prescribed daily doses and WHO defined daily doses of antibacterials at a university hospital. Br J Clin Pharmacol. 2006;61(5):585-591.
  7. National Nosocomial Infections Surveillance (NNIS) System report, data summary from January 1992 through June 2004, issued October 2004. Am J Infect Control. 2004;32:470-485.
  8. Berrington A. Antimicrobial prescribing in hospitals: be careful what you measure. J Antimicrob Chemother. 2010;65(1):163-168.
  9. Polk RE, Fox C, Mahoney A, Letcavage J, MacDougall C. Measurement of adult antibacterial drug use in 130 US hospitals: comparison of defined daily dose and days of therapy. Clin Infect Dis. 2007;44(5):664-670.
  10. Cefepime [package insert]. Shaumburg, IL: APP Pharmaceuticals; 2012. 
  11. Centers for Disease Control and Prevention. National Healthcare Safety Network. Medication-associated (MA) module. Atlanta, GA: CDC 2012. Accessed June 29, 2012.
  12. Polk RE, Hohmann SF, Medvedev S, Ibrahim O. Benchmarking risk-adjusted adult antibacterial drug use in 70 US academic medical center hospitals. Clin Infect Dis. 2011;53(11):1100-1110.
  13. Centers for Disease Control and Prevention Web site. Antimicrobial Stewardship for the Community Hospital: Practical Tools & Techniques for Implementation. Accessed October 11, 2012.


Gregory Marks, PharmD, BCPS, is the clinical pharmacy specialist in infectious diseases at TriStar Centennial Medical Center in Nashville, Tennessee. Greg received his PharmD from Northeastern University in Boston. He subsequently completed a PGY1 pharmacy residency at Tufts Medical Center in Boston and a PGY2 pharmacy residency in infectious diseases at Henry Ford Hospital in Detroit.


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