variable preventing separation of tNSAIDs from coxibs (6).
The whole blood assays also permit estimation of achieved
COX-isozyme selectivity in humans, which is the ratio of
isozyme inhibition at a given plasma concentration. Importantly,
achieved selectivity of NSAIDs varies as a consequence
of the dose administered.
The introduction of NSAIDs selective for COX-2, which
were developed to reduce the risk of serious gastrointestinal
complications—dependent, at least in part, on the inhibition
of COX-1—while achieving comparable efficacy, has raised
new concerns now centered on CV safety (7). Originally, these
concerns were reported solely for coxibs. Subsequently, we have
learned that some tNSAIDs may share a CV risk similar to
selective COX-2 inhibitors. The body of evidence consists of
data from clinical trials (8) and from a growing number of
observational studies, most of which have been performed
using large automated databases (9).
Inhibition of TXA2-dependent platelet function in vivo
occurs when platelet COX-1–dependent capacity to synthesize
TXA2 (as assessed by measuring serum TXB2 levels)
is reduced 95% (10). In fact, recent findings suggest that
local release of tiny concentrations of TXA2 from activated
platelets may play an important role in platelet thrombus
formation. They activate the tyrosine-kinase–based signaling
pathway (11), which may translate into full platelet
activation in the presence of weak platelet agonists or
subthreshold concentrations of stronger agonists. This leads
to the concept of functional COX-2 selectivity by NSAIDs,
namely, inhibition of COX-2 in the presence of an insuf-
ficient reduction of platelet COX-1 activity to translate into
inhibition of platelet function.
In the present study, we used data from the THIN (The
Health Improvement Network) database to evaluate the
association between prospectively collected information on
the frequency, dose, and duration of different types of
NSAIDs and the risk of nonfatal myocardial infarction
(MI) in the general population. Additionally, we verified the
functional COX-2 selectivity by average circulating concentrations
of the doses of tNSAIDs and coxibs, mostly taken
from the population of the THIN database, and found that
most tNSAIDs were as COX-2 selective as coxibs with
respect to platelet function. Then, we aimed to address the
hypothesis that the degree of inhibition of whole blood
COX-2 in vitro by plasma concentrations corresponding to
the average NSAID therapeutic dose in patients (an index
of drug potency/exposure) (12–14) predicts the relative risk
(RR) of MI for each individual NSAID functionally selective
for COX-2 observed in the general population.