Applying evidence-based medicine to formulary decisions

Pharmacists adjust criteria to evaluate conflicting trial data

"Evidence-based" is one term often heard at the ASHP meeting. In one presentation, "Applying the principles of evidence-based medicine to formulary decisions: Development of an innovative tool to evaluate conflicting data," pharmacists at the University of Pittsburgh Medical Center (UPMC) described how they developed grading criteria to evaluate a body of literature, especially when it is conflicting.

In 2003, the UPMC Pharmacy and Therapeutics Committee had approved guidelines developed to evaluate the quality of the literature. The previously published criteria were used to evaluate the quality of a single clinical trial in terms of how well it was designed, the results, and whether the results can be applied to practice, says presenter Shelby Corman, PharmD, assistant professor and clinical specialist in drug information at the university’s School of Pharmacy. These criteria consisted of a checklist of 10 items that are desirable attributes of a clinical trial such as randomization and control. The study then is assigned a letter grade of A, B, or C based on the number of criteria it meets.

Limitations to this approach, however, became apparent. For example, the criteria do not address the amount of data supporting a particular recommendation or how consistent the data are. Corman and her colleagues, therefore, wanted to develop grading criteria to address these components as well.

They began by looking at guidelines from the Agency for Healthcare Research and Quality (AHRQ). AHRQ defines quality, quantity, and consistency as the three aspects of the literature that should be evaluated when you are looking at a therapeutic recommendation, Corman says.

When comparing AHRQ’s criteria with the ones in place at UPMC, the researchers found that they were doing a good job in some aspects. Areas not covered included number of studies, sample size, and similar findings across multiple studies. A survey of the literature revealed no previously developed systems that evaluate all three of the quality, quantity, and consistency domains.

Based on the AHRQ recommendations and previously published guidelines, the pharmacists developed guidelines for what they call "composite grading." They use these guidelines to grade an entire body of literature and to address the components of quality, quantity, and consistency that have been identified by AHRQ. They do this by objectively assigning a point value to each domain. The point values are added for a composite score that indicates the strength of a therapeutic recommendation. Study quality, quantity, and consistency are each evaluated on a three-point scale, with higher scores indicating more favorable conditions.

The sum of scores for each domain is then used to assign a grade of A, B, or C to represent the strength of the body of evidence in support of a recommendation. The pharmacists also have a category E for recommendations supported only by expert opinion, with the caveat that this would be used infrequently. In addition, the risk-to-benefit ratio is indicated using the number 1 for a recommendation in which the benefit of the intervention proposed clearly outweighs the risk, and the number 2 for a recommendation in which the benefit of intervention does not clearly outweigh the benefit.

In her presentation, Corman gave an example of how the new criteria changed UPMC’s guidelines for prevention of radiographic contrast media-induced nephropathy. The new criteria allowed the pharmacists to re-rank these interventions "in a way that our P&T committee thought was reflective of how they should be used in practice," Corman says. "We considered that a validation of our new criteria."