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Chapter 11. Principles of Evidence-Based Prescribing

Brent G. Petty, MD

Medications are the principal tools doctors use to maintain health, reverse illness, and extend patients' survival, hopefully with good quality of life. Yet medications can also cause serious illness and fail to have the desired effect if they are used improperly. Additionally, medications can be extraordinarily expensive, and the cost to individual patients, to hospitals, and to our health system can become almost prohibitive. So the proper use of medications is critically important.

Before any medication is ordered in a hospital or prescribed for an outpatient, the prescriber needs to consider the (1) efficacy, (2) safety, and (3) cost of the medication, in that order of importance. Without efficacy for the condition being treated, no medication should be given. “It's not likely to be harmful” is no justification for trying something without demonstrated efficacy for the patient's problem, unless the intervention is in the setting of a clinical trial or the patient is informed of off-label use without evidence of benefit.

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Practice Point
  • Before any medication is ordered in a hospital or prescribed for an outpatient, the prescriber needs to consider the (1) efficacy, (2) safety, and (3) cost of the medication, in that order of importance. Without efficacy for the condition being treated, no medication should be given. There is a risk of toxicity with virtually all medications, so there must be a consideration of risk and benefit before starting or continuing medications.

Evidence for Efficacy

The quality of medical studies supporting the use of medications varies widely. In recent years, the quality of data has been graded by the groups reviewing the literature and making recommendations, such as the Chest guidelines for anticoagulation (Table 11-1). These grading systems consider the methodologies of the studies as well as the strength of the results.

Table 11-1 Grading System for Evaluating Evidence
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Table 11-1 Grading System for Evaluating Evidence
Strength of Recommendation
1 (Strong)2 (Weak)
Quality of Literature
A (High)

1A—Strong recommendation, high-quality evidence.

Consistent evidence from RCTs without important limitations or exceptionally strong evidence from observational studies

2A—Weak recommendation, high quality evidence.

Consistent evidence from RCTs without important limitations or exceptionally strong evidence from observational studies

B (Moderate)

1B—Strong recommendation, moderate-quality evidence.

Evidence form RCTs with important limitations (inconsistent results, methodological flaws, indirect or imprecise), or very strong evidence from observational studies

2B—Weak recommendation, moderate-quality evidence.

Evidence from RCTs with important limitations (inconsistent results, methodological flaws, indirect or imprecise), or very strong evidence from observational studies

C (Low)

1C—Strong recommendation, low or very low quality evidence.

Evidence for at least one critical outcome from observational studies, case series, or from RCTs with serious flaws or indirect evidence

2C—Weak recommendation, low or very low quality evidence

Evidence for at least one critical outcome from observational studies, case series, or from RCTs ...

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