Re: [FH] Re: ASA questions??
- My cardiologist prescribed 1/4 of an 81 mg tablet twice a week (simpler and
I suppose slightly less frequent than every three days), and if he tolerated
it after a month to up it to 1/2 of an 81 mg tab twice a week. (He was
starting ASA after not tolerating plavix in November.) I was considering
replying to your initial email about a whole baby aspirin every three days,
because it sounded like a lot to me as well (and I think I most commonly see
1/4 of an 81 mg mentioned), but then I came across the following (pasted
below message) from http://www.vetinfo4cats.com/catmed.html . My impression
based upon this is that an entire 81 mg tablet IS on the high end, but not a
complete anomaly in prescribing.
I think the most common issue with ASA (and plavix) is that it's hard on the
stomach. ASA seems to be better in this regard than plavix, probably in part
because it's dosed every three days instead of daily. I believe it can also
cause kidney/liver issues, just like most other heart meds; for plenty of
cats, that's not an issue. (My boy's ALT, a liver enzyme, went through the
roof after a week and a half on enalapril; it's part of the reason for
regular bloodwork.) Uncontrolled or internal bleeding is a risk with any
blood thinner, I think (in researching Patches' condition, I've heard
infrequent stories of internal bleeding in cats on both ASA and plavix, but
overall it seems more frequent with plavix.); the alternate risk of not
being on ANY blood thinner is the risk of clotting (which blood thinners
don't guarentee won't happen regardless, it's just thought to lower the
The nattokinase that Carol mentioned sounds like doesn't have the same risk
of stomach side effects as ASA or plavix, and it certainly doesn't have the
toxicity of ASA if not dosed or metabolized properly. If you and your vet (I
forget, are you with a regular vet or cardiologist? Vets probably have far
less experience dosing ASA, particularly for cats; it's historically been
used more often in dogs than cats. Regardless a cardiologist will have more
experience with cats on their preferred blood thinner, and the dosing.) do
decide to try ASA, I would definitely recommend starting on a lower dose to
see how your baby initially tolerates it, and looking into dosing
recommendations before settling on a final dose.
The relevant portion of the above link (note that it was written in 2001 -
standards may have changed, and many - by no means all - cardiologists have
switched to plavix as the first-line blood thinner since then):
*Aspirin dosage for cats*
*Question: *I believe the aspirin dosage you reccommend for cats is
incorrect on this page: http://www.vetinfo.com/catortho.html
You suggest 10mg/lb, but every other source I can find suggests 10mg/kg.
That makes the dosage you suggest more than twice the common
reccommendation. Here are some other resources:
Thank you for being concerned enough to write to us about the dosage for
There are published studies indicating that aspirin is safe when dosed from
10 to 25mg/kg every 48 to 72 hours and one study indicating no problems when
it was dosed at 162mg/cat once a week. We use up to 10mg/lb in our
practice, even though it is at the higher end of the dosage scale. We
usually do not exceed 81mg per cat and I probably should indicate that in
our answers online, since this is often closer to 5mg/kg in large cats.
Mike Richards, DVM 10/15/2001
[Non-text portions of this message have been removed]
- Thanks everyone for replying. I did some reading and found some google book excerpts of vet medicine textbooks that indicated that asa in doses of 25mg/kg twice weekly did not show toxicity. My cat is 16lbs so 81mg is just over 10mg/kg. I mentioned my concern about asa for cats and my vet said the dose of 81mg every 3 days was safe. I will follow with again about this.
> I think the most common issue with ASA (and plavix) is that it's hard on theMy cat tolerated plavix for roughly 18 months. It was always given to
> stomach. ASA seems to be better in this regard than plavix, probably in part
> because it's dosed every three days instead of daily.
her after she had eaten. She did not appear to have tummy upset
The problem with high doses of aspirin in kitties, more so
than the tummy upset is that kitties lack an enzyme, produced
by the liver (glucuronyl transferase) that is required to metabolize
not only aspirin but also other NSAIDs. This means that it takes longer
for aspirin to clear the kitty's system (3 day dosing) and it makes it
much easier to overdose a kitty. Especially a compromised
If there are concerns, then one could further consult with one's vet
or have a liver panel done to see whether there are problems.
Additionally some NSAIDs can interfere with the function of ACE inhibitors.
ACE inhibitors work, in part by dilation of blood vessels in the kidneys and
some NSAIDs interfere with this dilation. I don't recall whether aspirin is one of
A baby aspirin is typically 81 mg of aspirin.
As far as a specific dose, the FATCAT study that is looking at the effect
of plavix vs. aspirin for prevention of a second clot in a group of kitties
that have already experienced a clot is:
"clopidogrel/plavix (18.75 mg PO q 24 hours) or aspirin (81 mg PO q 72 hours). The dosages chosen for the study drugs are based on the standard accepted dosing regimen for aspirin and preliminary data from clopidogrel pharmacodynamic studies."
"Antiplatlet aggregating therapy may be considered when severe left atrial
enlargement is present, when spontaneous echo contrast is evident in the LA or
LAV, or when cats have have had preveious thromboembolic episodes. Aspirin may
be used, dosed at approximately 80mg every three days. Other agents are presently
under investigation such as clopidogrel (Plavix). Low molecular weight heparin
drugs are added when cats have thromboembolic complications. Two particular
agents, enoxaparin (Lovenox) and dalteparin (Fragmin), have received the most
attention. Both drugs are expensive but appear to have a far greater safety margin
than unfractionated heparin. Fragmin (100 U/kg q 12-24hrs SQ) or enoxaparine
(1mg/kg q 12 hrs SQ) have been used relatively safely. This dose of fragmin,
however, may be too little- or the frequency too low, to be efficacious. Administration
rates of every 6 to 8 hours are generally impractical, however, for long term
administration. Hyperkalemia can occur acutely as a result of re-perfusion injury.
Continuous ECG monitoring is valuable during the first 3 days of hospitalization.
Periodic evaluation of BUN and electrolytes are useful."
Hope this helps.