Aspirin for heart attack: Chew
You’ve always been healthy, but you seemed to run out of steam
at your wife’s 60th birthday dinner last week. And now your chest
feels heavy, as if you’re in a vise. You take some antacids,
even though it’s 7:00 a.m. and you haven’t even had breakfast.
But you get no relief, and the pain is spreading to your jaw and shoulder.
You call your wife, who takes one look at you and rushes to the phone.
After calling 911, she brings you an aspirin and some water.
Your wife got it right: You may be having a heart attack, and you need
to get to the hospital fast. You also need to get some aspirin into your
system quickly — but should you chew the tablet or swallow it?
The reason you need aspirin is the same reason you should call 911
without delay: A heart attack is a dynamic event, and early intervention
can limit the damage. The paramedics can give you oxygen and medication,
and they’ll monitor your blood pressure and heart rhythm to forestall
complications as they speed you to the ER. In the hospital, doctors will
take EKGs and blood tests to see if you are having a heart attack; if
so, they will usually try to open the blocked artery with an angioplasty and stent or,
if that’s not available, with a clot-busting drug.
It’s modern cardiology at its best, and it has improved considerably
the outlook for heart attack victims. But how can a humble aspirin tablet
add to high-tech medicine, and why is speed so important?
Most heart attacks develop when a cholesterol-laden plaque in a coronary
artery ruptures. Relatively small plaques, which produce only partial
blockages, are the ones most likely to rupture. When they do, they attract platelets to
their surface. Platelets are the tiny blood cells that trigger blood
clotting. A clot, or thrombus, builds up on the ruptured plaque.
As the clot grows, it blocks the artery. If the blockage is complete,
it deprives a portion of the heart muscle of oxygen. As a result, muscle
cells die — and it’s a heart attack.
Aspirin helps by inhibiting platelets. Only a tiny amount is needed
to inhibit all the platelets in the bloodstream; in fact, small amounts
are better than high doses. But since the clot grows minute by minute,
time is of the essence.
To find out how aspirin works fastest, researchers in Texas asked 12
volunteers to take a standard 325-mg dose of aspirin in three different
ways: by swallowing a tablet with 4 ounces of water, by chewing the tablet
for 30 seconds before swallowing it, or by drinking 4 ounces of water
with Alka-Seltzer. Each subject tried all three methods on an empty stomach
on different days. The scientists monitored blood levels of aspirin and
its active ingredient, salicylate, at frequent intervals, and
they also measured thromboxane B2 (TxB2), an indicator of platelet
activation that drops as platelets are inhibited.
By all three measurements, chewed aspirin worked fastest. It needed
only five minutes to reduce TxB2 concentrations by 50%; the Alka-Seltzer
took almost 8 minutes, and the swallowed tablet took 12 minutes. Similarly,
it took 14 minutes for the chewed tablet to produce maximal platelet
inhibition; it took Alka-Seltzer 16 minutes and the swallowed tablet
26 minutes (see graph below).
Aspirin can help prevent heart attacks in patients with coronary artery
disease and in healthy men over 50 years of age. Only low doses, between
81 and 325 mg a day, are needed. But people who think they may be having
an attack need an extra 325 mg of aspirin, and they need it as quickly
as possible. For the best results, chew a single full-sized 325-mg tablet,
but don’t use an enteric-coated tablet, which will act slowly even
if chewed. And don’t forget to call 911, then your doctor. It’s
a contemporary update on the old reminder to take two aspirin and call
in the morning — and it’s good advice to chew over.
Antiplatelet effect of chewed, swallowed,
and dissolved aspirin
Chewing aspirin hastens its antiplatelet effect, as measured
by the reduction in blood thromboxane B2 levels. It took only
5 minutes for patients who chewed aspirin to achieve a 50% reduction
in baseline levels, versus almost 8 minutes after they took it
in a solution and 12 minutes after they swallowed it whole.
Source: American Journal of Cardiology Vol. 84, p.
May 2005 Update
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