One can usually find many sources of information about drugs: FDA website, drug company websites and technical reports, VIN,
journals, trade magazines, and so on. The important skill required of veterinarians is to assess that information to determine
its usefulness in your daily practice. Below are some principles of evaluating drug information, with the goal of improving
treatment and the practice of medicine.
Principles of Evidence-Based Medicine
Evidence-based medicine is the approach to making medical and therapeutic decisions that is "the integration of best research
evidence with clinical expertise and owner/manager values." This approach differs from the other prominent methods of decision-making,
the expert-based or apprentice-based approach, which predicates clinical decisions on what has been done before and on what
the "experts" say, whether the experts are the clinicians who taught you in veterinary school or the authors of the review
articles you read or the presenters at continuing education seminars. This approach to making clinical decisions emphasizes
just-in-time learning, rather than just-in-case learning, during which you search for assistance with decision-making on the
basis of the cases you are presented with.
Evidence-based medicine suggests the explicit use of the following steps in decision-making about drugs:
1. Ask a clinically relevant and answerable question about the patient or patients. One commonly used approach is PICO,
which refers to asking a question with the elements of patient, intervention, comparison, and outcome. An example of a PICO
question encountered in bovine practice might be:
2. What antimicrobial regimen (I) is most likely (C) to result in minimal weight loss (O) in stocker calves (P) on grass
3. Locate the best evidence to answer the question.
4. Hierarchy of evidence levels outlined below
5. Critically appraise the evidence for validity, impact and applicability.
6. SIntegrate the appraisal with clinical expertise and the patient's and client's unique biology, values, and circumstances.
The critical appraisal step above (Step 3) often includes the assignment of a "level of evidence" to the evidence located
in Step 2. There are as many schemes for assigning levels of evidence as there are advocates of evidence-based medicine, but
one scheme designed to address the types of data for veterinary species was originated by the veterinary expert panels at
the U.S. Pharmacopeia, when they were developing drug information monographs. Their scheme includes assigning a level of evidence
(1-6) and a quality grade (A-E). The level of evidence refers to the type of data, as follows: \
1. Species-specific evidence from at least one large randomized and controlled trial (RCT) or multiple small RCTs
2. Species-specific evidence from a small RCT, disease models, large case studies, pharmacokinetic studies using surrogate
endpoints, or evidence from well-designed trials in a different species that is considered appropriate for comparison
3. Dramatic results from either well-designed, species-specific trials without controls or small case studies
4. Pharmacokinetic studies without surrogate endpoints
5. In vitro studies
6. Opinions of respected authorities on the basis of clinical experience or reports of expert committees
The quality grades include: A (Good evidence to support a recommendation for use), B (Moderate evidence to support a recommendation
for use), C (Insufficient evidence to support a recommendation for use), D (Moderate evidence to support a recommendation
against use), and E (Good evidence to support a recommendation against use).
These levels and grades are assigned to each piece of evidence, e.g., [B-3]. The purpose of assigning a level of evidence
to a particular set of data is to weigh evidence with a higher level more heavily. In addition, consideration of levels of
evidence encourages us to search for the best evidence, rather than stopping at the first evidence that we find.