Today's USA Today has a nice summary of the recent controversies over drugs
that are being removed from the market because of an unacceptable increased
risk of side effects. Under special scrutiny these days are a class of drugs
known as COX-2 inhibitors. According to
MedicineNet,
COX-2 inhibitors are newly developed drugs for inflammation that
selectively block the COX-2 enzyme. Blocking this enzyme impedes the
production of the chemical messengers (prostaglandins) that cause the pain
and swelling of arthritis inflammation. Cox-2 inhibitors are a new class of
nonsteroidal anti-inflammatory drugs (NSAIDs). Because they selectively
block the COX-2 enzyme and not the COX-1 enzyme, these drugs are uniquely
different from traditional NSAIDs.
www.medicinenet.com/cox-2_inhibitors/article.htm
One particular drug in this class, Vioxx (generic name: Rofecoxib), has
been voluntarily removed from the market by its manufacturer, Merck, because
this drug was associated with an increase in the risk of serious
cardiovascular events. Two other drugs in this class (Celebrex/Celecoxib and
Bextra/Valdecoxib) also have data suggesting an increase in the risk of
cardiovascular problems, and there are calls to pull these drugs off the
market also.
There are a lot of political comments about this issue, and while these are
very important, it is also important to recognize that detecting drugs that
have an increased risk of side effects is a difficult job.
The first problem is with most of the randomized trials that drug companies
use to submit these drugs for government approval. These trials typically do
not last long enough, nor have sufficient numbers of patients to get a handle
on rare but important side effects.
Sometimes patients who tolerate a drug poorly will drop out of the trial.
This causes serious problems unless the dropouts are accounted for properly
and analyzed appropriately.
The second problem is that prescribing physicians do not carefully consider
the limitations of these randomized trials. Sometimes a drug will be
prescribed for a different condition than the one originally submitted, a
practice known as off-label prescribing. This is a difficult area, because
drug companies cannot advertise or market a drug for a condition other than
the one that it originally got approval for. But these companies will often
find covert and subtle ways to encourage and promote off-label use. From the
perspective of side effects, off-label use leads to a lot of unknowns,
because the types of people who have the new condition will be quite
different from those in the randomized trials and may have a radically
different side effect profile.
Often these trials exclude patients who are more likely to develop side
effects. That would be okay if the same exclusion found its way into medical
practice, but often this is forgotten or overlooked.
The third problem is that data on the side effects of drugs is inherently
ambiguous. If you want to show that a drug is efficacious, you can usually
point out two or three outcomes that would definitively indicate whether the
drug works or not. But the possible side effects for a drug is usually large
and unwieldy. Most statistical approaches work well only when the number of
outcomes being evaluated is small and manageable.
Steve Milloy, author of the Junk
Science web page, also points out that side effect data is often a
secondary endpoint in most clinical trials.
None of the clinical trials giving rise to the questions about Vioxx,
Celebrex and Aleve were, after all, specifically designed to test whether
the drugs posed a heart attack or stroke risk. The data on Vioxx came from
a study of gastrointestinal effects; the Celebrex data came from a cancer
prevention study; and the Alleve data came from an Alzheimer's prevention
study. --
www.foxnews.com/story/0,2933,142453,00.html
In actuality, there were two trials that indicated problems with Vioxx: the
VIGOR trial (VIOXX Gastrointestinal Outcomes Research), published in the
November 23, 2000 issue of NEJM and the APPROVe trial (Adenomatous Polyp
Prevention on VIOXX), which remains unpublished, but which was stopped early
in September 2004. According to a Merck press release, the APPROVe trial
was designed to evaluate the efficacy of VIOXX 25 mg in preventing
recurrence of colorectal polyps in patients with a history of colorectal
adenomas. In this study, there was an increased relative risk for confirmed
cardiovascular events, such as heart attack and stroke, beginning after 18
months of treatment in the patients taking VIOXX compared to those taking
placebo. --
www.vioxx.com/vioxx/documents/english/vioxx_press_release.pdf
For Celebrex/Celccoxib, the APC trial (Adenoma Prevention with Celecoxib),
a large colorectal cancer prevention trial, was stopped early on December 17,
2004 because the patients taking Celecoxib had an increased risk of
cardiovascular events (Cardiovascular death, myocardial infarction, or
stroke). In the placebo group, there were 6 events among the 679 patients. In
the Celecoxib 200 mg BID group, there were 15 events among 685 patients. In
the Celecoxib 400 mg BID group, there were 19 events among 671 patients. The
relative risk for both Celecoxib groups combined versus placebo was 2.8 (95%
CI 1.2 to 6.7). Interestingly enough, the Pre-SAP trial (Prevention of
Spontaneous Adenomatopus Polyps Trial), another cancer prevention trial,
showed no change in the risk of cardiovascular events (Placebo 11/628 events,
Celecoxib 400 mg QD 16/933 events, relative risk 1.0, 95% CI 0.5 to 2.1).
When you are evaluating the side effects of a drug, you need to consider
the individual values and preferences of the patients. What are the benefits
of the drug for this particular patient? For many patients there are good
alternative drugs; for others, this may be the only drug that offers relief.
What is the patient's risk profile for the potential side effects. A healthy
patient who has a vanishingly small chance of seeing a side effect may be
willing to tolerate a doubling or tripling of risk. A patient who is already
at a high level of risk may not be so willing. A recent FDA guidance on these
drugs suggests
Patients who are at a high risk of gastrointestinal (GI) bleeding,
have a history of intolerance to non-selective NSAIDs, or are not doing
well on non-selective NSAIDs may be appropriate candidates for Cox-2
selective agents. --
www.fda.gov/bbs/topics/ANSWERS/2004/ANS01336.html
These comments are not intended to exonerate the drug companies or the FDA.
Some people have suggested that the drug companies have marketed these drugs
too aggressively, have not performed the appropriate safety tests for these
drugs, and/or have failed to inform the public about what they knew about the
risks of these drugs. Others have suggested that FDA has an inherent conflict
because of its role in drug approval and that drug safety monitoring should
be handled by an independent agency. Whether or not these allegations are
true, it is still worth remembering that testing for side effects is very
difficult to do.
