Can I give my dog aspirin?

Aspirin is an NSAID or Non Steroidal Anti Inflammatory Drug. It is one of a whole class of drugs that are used, among other things, to reduce inflammation and relief pain. Common dog NSAIDs include: Previcox, Arquel, Rimadyl, Metacam, Deramax, Ketoprofen, Zubrin, Feldene, and Etogesic. There is many, many more used in human medicine. To save money, many people will turn to buffered or enteric coated aspirin to give their dog to help with his or her arthritic pain. Or sometimes, they just think that aspirin "can't hurt".

However aspirin may not be as safe as you think. It may be worth the extra money to use prescription dog NSAIDs. Here are some things to consider before you give your dog aspirin:

acetylsalicylic acid

There are many differences between each NSAID, but let's focus at just one of the important characteristics that separates NSAIDs. You may have heard about COX-1 and COX-2. These are the enzymes that are inhibited by NSAIDs. It is the main method with which they work. COX-2 is induced in inflamed tissues and is usually not present in normal tissues. Inhibiting this enzyme helps reduce inflammation and pain. COX-1 is considered a 'constitutive' enzyme and is present in most tissues all of the time. COX-1 is responsible for maintaining stomach blood flow, the protective mucous layer, and stimulating the outer cell layer of the stomach. Additionally COX-1 is also important in platelet function (ability to clot blood). Inhibiting COX-1 also reduces kidney blood flow.

NSAIDs inhibit both COX-1 and COX-2. Therefore the ratio with which an NSAID does this becomes very important. The higher the number, the less the drug inhibits the COX-1 and has less side effects with respect to this enzyme. An NSAID with a high number is considered to be 'Cox-1 Sparing'

There are slight differences in the published numbers but they are similar with their relationship to aspirin.

So what does this really mean? Well, it means that aspirin inhibits the good COX-1 enzyme 117 times more than Metacam. At the very least aspirin inhibits the COX-1 enzyme 19 times more than Rimadyl and at the worst, 60 times more. And compared to Previcox? At the very least aspirin inhibits the COX-1 enzyme 1371 times more than Previcox. WOW! Maybe this is why companies spent time developing these new dog NSAIDs.

 In a human dental surgical study, flurbiprofen at both the 25mg and 50mg study were superior to 650mg of aspirin¹! While we do not use flurbiprofen, it does highlight the advancements with the newer NSAIDs. There are several studies which show higher pain control with the newer NSAIDs.

Damage of the stomach and intestines is one the most common and serious side effects of NSAIDs. Dogs are also considered to be "exquisitively sensitive" to stomach ulceration from NSAIDs².

There are several mechanisms that are suspected for how the stomach becomes damaged. There is evidence that the damage may likely be a combination of these mechanisms. They include:

• Prostaglandin Inhibition through COX-1 activity
• Increased stomach acidity
• Decrease in the protective mucous layer of the stomach
• Decrease in bicarbonate (natural buffers) secretion
• Decreased formation of the protective outermost cell of the stomach layers (a process called decreased epithelialization)
• Decreased stomach blood flow of the mucosa
• Direct irritation of the acidic drugs
• "..Salicylates [like aspirin versus other NSAIDs] cause local damage due to "back diffusion" of acid which causes injury to mucosal cells [those that line and protect the stomach] and submucosal capillaries [blood supply].³" 'Back diffusion' involves the interference of electrolyte enzyme pumps. There is no prescription dog salicylate.

 "Unfortunately, there is no sensitive indicator of gastrointestinal bleeding in dogs and damage may be quite extensive before signs are evident.⁴" Thus many dogs may have some level of stomach damage, bleeding, and ulceration without showing any clinical signs. If an illness arises, the presence of aspirin may compromise the pet.

"But it is buffered!" Buffering agents usually include Aluminum hydroxide and Magnesium hydroxide (Maalox is comprised of these two) to reduce stomach acidity. That's all. Simple reduction of stomach acid just doesn't seem enough does it?

What about enteric coated aspirin? A study showed that the risk of 'gastrointestinal' bleeding was not reduced by enteric coating of aspirin⁵.

This reminds me of the saying, "You get what you pay for." There is a reason why companies spent thousands of dollars to come up with newer, safer, more effective NSAIDS. It is because they are safer and more effective.

But are they really that cheaper? Yes, per pill aspirin is cheaper. However if it is properly going to be used, there should be regular blood testing just like any other NSAID. Additionally there are other concerns with aspirin which may hurt your pet such as platelet function and impaired cartilage function. If buffered aspirin is just being given without blood testing and there is any low level of liver or kidney impairment, aspirin may be further damaging your pet. Additionally if regular blood testing is not being performed, then the reaction of NSAID liver toxicity might be missed. When we consider these concerns, the savings does not seem as great.

There are several studies that evaluate Aspirin and its harmful effects on cartilage, the very organ we are trying to help during arthritis.

1. A human study⁶ evaluated the effects of Metacam (meloxicam) and Aspirin (acetylsalicylic acid) on cartilage. The study showed the Metacam had no negative effects, while aspirin caused "decreased proteoglycan production and cell proliferation". Proteoglycans are the building blocks to the cushion matrix that makes up cartilage. Without cell reproduction, the cartilage cannot heal. This would indicate that aspirin is harmful to human cartilage. There is much reason to suspect that the same is true for canine cartilage.
2. A canine study⁷ showed that aspirin had "had detrimental effects on chondrocyte[cartilage cell] viability, GAG [Glyco Amino Glycan, an important precursor to the cartilage cushion or matrix]  production, or both."
3. A bovine articular cartilage study⁸ concluded that, "Salicylates may suppress cartilage proteoglycan synthesis".

This fact is also being discussed and taught during Veterinary Continuing Education seminars.

1. "Conventional non-specific NSAIDs including indomethacin, naproxen, diclofenac, and aspirin have been shown to slow fracture healing, alter mineralization and inhibit Haversian system remodeling [the Haversian system is the microscopic structure and healing mechanism of the bone] in several (rabbit, rat, mouse) models."⁹
2. "Some NSAIDs (including aspirin, naproxen, and others) have been shown to impair the metabolic function of canine chondrocytes [cartilage cells] harvested from joints affected with osteoarthritis, and others such as carprofen [Rimadyl] have a lesser effect.¹⁰" - Bernie Hansen, DVM, MS

The current studies document that the older NSAIDs like aspirin are harmful to the cartilage, while other NSAIDs like Rimadyl has lesser effect, and that "all chondroformative processes were unaffected by meloxicam [Metacam]"¹¹.

                Take home message - not all NSAIDs are the same, some are much safer.

Aspirin Impairs Platelet Function

While you may have heard about this fact, did you know that when dosing for pain relief in dogs, the dose of aspirin is twenty to fifty times greater than the dose of aspirin for inhibiting platelet aggregation? NSAIDs inhibit platelet function through the inhibition of COX-1¹². This mechanism becomes important when we think of the COX-2 to COX-1 ratios of the various NSAIDs.

What about the others? Well, "Coxibs such as celecoxib, and rofecoxib do not inhibit platelet function in humans, and deracoxib [Deramaxx] does not affect buccal mucosal bleeding time in dogs (Deramaxx label).  ...neither carprofen nor meloxicam are associated with prolongation of buccal mucosal bleeding times in healthy dogs (Hickford 2001, Mathews 2001)." - Lauren A. Trepanier, DVM, PhD, DACVIM, DACVCP. The active ingredient of Previcox is firocoxib and is a member of the Coxib family like Deramaxx.

Rimadyl and Meloxicam do have some platelet inhibition, but the level is much less when compared to aspirin. This is why aspirin is singled out in many texts to be of high concern¹³.

                While the mild to moderate pain control from aspirin lasts twelve hours or so, the negative effects can last a couple of weeks after dosing. For this reason, when changing NSAIDs, you must wait much longer with aspirin. "If changing NSAIDs due to a lack of efficacy, a 7 day washout period is a conservative time. Changing therapy can be accomplished within a few days... [However] a washout period changing to or from aspirin may be up to 14 days."¹⁴

                Why is this? Not only because of how it affects COX-1 but the way it affects COX-2. "Following aspirin therapy, upregulation of lipoxin production via acetylated COX-2 enzyme has been identified as an important mechanism of GI mucosal healing and homeostasis. Following aspirin therapy, caution is recommended when switching to another NSAID..."¹⁵

Aspirin, being a salicylate, has a longer list of drug interactions. Here is the list for Aspirin¹⁶:

1. Drugs that alkalinize the urine
2. Carbonic anhydrase inhibitors (e.g.,acetazolamide, dichlorphenamide)
3. Urinary acidifying drugs (methionine, ammonium chloride, ascorbic acid)
4. Furosemide (Lasix)
5. Phenobarbital
6. Corticosteroids (Prednisone, Prednisolone, Triamcinolone, Dexamethasone, Fluticasone, Cortisone, Depo-Medrol)
7. Phenylbutazone and other highly protein bound drugs
8. Heparin
9. Oral anticoagulant therapy
10. Probenicid or sulfinpyrazone
11. Spironolactone
12. Methotrexate, valproic acid, phenytoin
13. Penicillins (Ampicillin, Amoxicillin, Clavamox, Augmentin, etc...)
14. Sulfonamides (Albon, Zonisamide)
15. Tetracycline
16. Digoxin
    
17. Aminoglycoside antibiotics (amikacin, gentamicin, kanamycin, neomycin, streptomycin, tobramycin, etc...)  

For comparison, here is Metacam's list¹⁷:

1. Highly protein bound drugs, including warfarin, phenylbutazone, etc. SAME AS ASPIRIN
2. NSAIDS: aspirin, flunixin, phenylbutazone SAME AS ASPIRIN
3. Corticosteroids SAME AS ASPIRIN
4. ACE inhibitors INSTEAD ASPIRIN INTERACTS WITH THREE OTHER COMMON DOG HEART MEDICATIONS
   

For the same pharmaceutical drug reference, aspirin has a lot more interactions. Penicillins (amoxicillin, Clavamox, Augmentin, Ampicillin), sulfonamides (albon, zonisamide), tetracycline and aminoglycosides are all antibiotics. Did you know that you need to stop, reduce or alter giving your pet's aspirin with any of these antibiotics? Aspirin displaces these protein bound drugs, "thus increasing free drug levels and pharmacologic effect..." of these medications. This may lead to increase risk of side effects by these other medications. Thus your pet might be at higher risk for a negative drug reaction of these antibiotics while on aspirin.

And what about the other drug reactions with aspirin? Spironolactone, furosemide (lasix) and digoxin are common heart medications. Corticosteroids are often used in allergies or even arthritis treatment. Methionine is a common medication that is given over the counter to stop the 'yellow grass effect from urine'. Phenobarbitol is a common anti-seizure mediation. Furthermore, the interaction with drugs that both raise or lower the urine pH covers a lot of other medications and over the counter supplements.

                Aspirin supplementation is a whole lot more complex that just something you can give over the counter.

Metacam

Probably but not necessarily; it does mean that you should sit down and talk with your veterinarian as to which of the various NSAIDs might be the best for your dog. Remember that the use of aspirin may have many side effects such as cartilage damage, impaired platelet function, and gastric ulceration which may not have any outward signs. To rationally use aspirin instead of another NSAID, the benefits of aspirin that are to be gained in your pet must out weight these negative effects.

      This article is not mean to imply that all the other NSAIDs are safe and without any side effects. Quite the contrary; one of the goals of this article is explain that NSAIDs can have a variety of interactions within the body. Also any pet can have a serious drug reaction such as the 'idiopathic hepatopathy' to any NSAID.  Most pets will not.

     The difference with aspirin is that not only is there the same risk of a liver reaction but there are negative effects that are virtually guaranteed such as cartilage damage and a much broader range of drug interactions. Furthermore, the data supports that the safer prescription NSAIDs will also provide greater pain relief for your pet.

     However despite all this, Rimadyl, Deramaxx and Metacam still have more negative comments on the internet than aspirin. My theory for this is that the prescription medications cost more and when they have been prescribed by a veterinarian and have serious negative effects; there is a greater emotional response. If you paid for a medication and then your family member has serious health concerns because of it; it would understandably make you feel angry, helpless and infuriated. This does not mean that all NSAIDs are bad and it is a mistake to think that then aspirin is safer because there is less internet condemnation.

     Furthermore, when clients are giving aspirin; it is common to see it at too low of a dose to adequately relief pain but high enough to create problems. I also commonly hear from clients that their pet is responding and helped by these lower doses. This would indicate that the pet would respond even so much more to a drug that is 1) at an appropriate dosage and 2) having less cartilage effects.  As many of the dogs that are being managed with aspirin are not getting routine blood testing, it is very possible that many cases are being missed where the aspirin is causing some level of kidney and/or liver damage.

     My dog and best friend Effany could not take NSAIDs. She had a very negative reaction to Metacam. Despite this, I have used this in other dogs I have owned and I will continue to prescribe it because I believe that it is a good medication to relief pain and is safe in most pets if properly monitored.

1. Only use it on the advice and consent of your veterinarian
2. Use it at the veterinarian's prescribed dose
3. Never mix it with other NSAIDs
4. Treat it like you would any other NSAID. Blood tests should be run prior to starting the medication, approximately two weeks after starting therapy and then every 6-12 months thereafter - or as recommended by your veterinarian
5. Monitor closely for signs of reactions
6. Always remind your veterinarian that your pet is on Aspirin before your pet has any surgery or is given any other medications. Remember, medications that come from your veterinarian are easily reviewed in the chart. Aspirin may only be a small notation on a previous visit's exam. As we have seen, aspirin has many drug interactions.
7. Talk to your veterinarian before you use any other over the counter medications, especially those that may alter the urine pH.

Click here for 1800-PetMeds.com

As of September 2009, at www.1800petmeds.com here are the prices (non-generic) for a 50 lb dog:

• Deramaxx (deracoxib) $1.44 per day
• Metacam (meloxicam) $1.43 per day
• Previcox (firocoxib) $1.23 per day
• Rimadyl (carprofen) $0.61 per day

These prices will vary with weight. Also depending upon the strength of the pill and the pet's weight, one medication may be easier to dose and may be cheaper in one drug versus another.

                We have Previcox, Arquel, Rimadyl, Metacam, Deramaxx, Ketoprofen, Zubrin, Feldene, and Etogesic. There is definitely a best NSAID out there but it is different for each dog. I will say that Ketoprofen and Arquel (Meclofenamic Acid) are generally not recommended.

                For chronic arthritis and osteoarthritis the most common choices are Rimadyl, Metacam, Deramaxx and Previcox. I recommend that you ask and discuss the choices with your veterinarian. As we have learned with aspirin, the COX-2 to COX-a ratio is not the only method to evaluate these medications. Each one has pros and cons. Furthermore the available doses and weight of your pet may also help influence the choice of NSAID.

Menhaden Fish - source of Omega 3 FA

                There are many good options. Glucosamine, Chondroitin, MSM formulations can help. It is important to note though that if you use it, Glucosamine HCl is absorbed 1.7 times more than Glucosamine sulphate. For this reason, dog formulations are generally better.

                Omega 3 Fatty Acids found in fish oils can help reduce pain and inflammation. (Please see article: Essential Information on Essential Fatty Acids). The prescription food by Hill's Science Diet called J/D works through the use of high levels of fish oils which are obtained from menhaden fish without any artificial preservatives (absolutely no ethoxyquin). The food is preserved with tocopheral (from soybeans and is a source of vitamin E), citric acid and rosemary extract. The amount of Omega 3s in one cup of food is 3374mg. So can I just give my dog some fish oil capsules? Well, a 60lb dog would need to take 49 capsules per day of a high density pure fish oil to reach the amount in the 4 cups of J/D needed to feed your dog¹⁸. Whew! That's a lot of pilling!

                How well does J/D work? Well, Hills took it to the FDA to run the same tests that a new drug coming out on the market would have to prove in order to pass. J/D had no problems! J/D has been proven to dramatically reduce pain and joint inflammation in dogs suffering from osteoarthritis. Ask your veterinarian about this food! Note: contraindications: J/D should not be given to overweight dogs or those at risk or suffer from pancreatitis.

                Tramadol is another alternative medication. Tramadol is a safe, inexpensive pain medication. Unfortunately it does not reduce inflammation or help with healing but is wonderful as an additional or even sole medication for pain.

                Note that multi-modal drug therapy is often the key to maintaining a pain free pet. These medications and nutriceudicals can be used together, such as combining an NSAID, glucosamine, J/D and tramadol. This can help maximize pain as each of these works in a different way. Always ask your veterinarian before combining any medication or nutraceudical.

                Other medications such as gabapentin, corticosteroids, morphine, etc... can also be used in some situations. Acupuncture, K-Laser therapy, magnet therapy, physical therapy, swimming, weight management and massage may also help reduce chronic pain from arthritis.

                I hope this article has helped not only explain and highlight some of the dangers of aspirin but also give you some understanding of NSAIDs and provide some ideas and options for you to ask your veterinarian about. In the end, the goal is to keep your dog comfortable in the safest way possible.