It is understood, broadly speaking, that drugs of the same class confer the same merits/risks, though one may be more efficacious and safer than the other. The drug class paper from the JAMA series talks about how to discern, using the literature, the superior drug by providing a hierarchy for grading studies1.
- Drug Class
- drugs that share a similar structure and mechanism of action, therefore conferring roughly similar pharmacologic effects. Further, as discussed subsequently, extrapolation using the heuristic is known as the Drug Class Effect.
When comparing trials studying different drugs of the same class, RRR2 should be consulted rather than the absolute treatment effects (such as ARR or NNT) on account of potential baseline risk differing between trials; ARR will vary quite a bit, regardless of the relative efficacy of the drug, making it a useless metric.
For instance, let us assume that Trial A—due to different inclusion/exclusion criteria, geographic location, time period, etc.—enrolls patients with higher baseline risk relative to Trial B. Precisely because of this, Trial A’s ARR is higher at 5%, whereas ARR for Trial B is 1%. However, the RRR is the exact same at 25%.
This illustrates an important principle: a drug may seem to only confer modest effects in low-risk patients but simultaneously seem highly efficacious in high-risk patients—even if the biological effect is proportionally the same. In comparing two trials, it is therefore imperative to note that one drug trial may have a higher baseline risk, hence producing an illusory, higher efficacious result.
As such, a drug class effect is observed when the RRR is roughly the same for two drugs, however, simply because two drugs produce the same immediate effect, it does not allow us to accept a priori that similar clinical outcomes can be expected. There may also be side effects outside of the shared class of action that may confound this erroneous heuristic. We therefore cannot extrapolate clinical outcomes from a RCT of one drug to another drug within the same class not yet subject to such studies.
A subsequent post will discuss the levels of evidence employed in order to discern the superior drug of a class.