Body

VetInfo Digest December 2004

Table of Contents:

Pain Relief:

General Information

NSAIDS

Narcotics

"Others"

Antidepressants

Corticosteroids

Acupuncture

Pain Relief Without Medication

This Month's Note:

If your pet is in pain there are a large number of options for controlling the pain. I wrote this month's issue with the intention of pointing this out by providing basic information on a large number of pain relief options. If your pet is in pain, or might be in pain, there are enough options for pain relief that most pets should not have to tolerate long term uncontrolled pain. Unfortunately, there are still a few exceptions but hopefully this month's issue will at least help you find some option that might work for your pet if and when the need arises.

The new NSAID drugs are great for chronic arthritis but if you can't afford them there are other options. The place that most of my clients fail to use adequate pain relief is chronic arthritis. If you talk to people who have this I think that you will find that most of them feel that they would take moderate risks to obtain relief from pain. Many of my clients want to find totally risk free pain relief for chronic arthritis or they don't want to give medications to their pets. This is simply unrealistic. All medications have some risk -- the question that you have to ask is would you take this risk if it was your pain? If you don't know, find someone who has the same condition as your pet and ask them what they would do. I think that you will find that most people who have conditions that cause chronic pain are willing to take reasonable risks to alleviate the pain -- and some would take very large risks. If you would take this risk for yourself you owe it to your pet to do the same for him or her.

Pain relief has become much more important in veterinary medicine over the time that I have been in practice. I am troubled by the time it took me and my profession to realize that pain relief is a major benefit to almost all patients in pain. I could have, and should have, helped a huge number of patients feel better after surgery, after injuries and during painful medical conditions. This is really one of those times when I wish that I had been the voice crying in the wilderness of this issue. All I can say in my defense is that I at least I did listen when other people asked the right questions. It takes a very long time to overcome the inertia of years of ignoring a problem, though. Even now I have to remind myself sometimes to include pain relief in the treatment protocol after a surgery or when I am treating a potentially painful disorder.

There are still situations where it is hard for me to figure out how to deal with the potential for pain or existence of pain. The most common of these situations is dental disease. As an example, most veterinary dental specialists are in agreement that feline odontoclastic resorption lesions (FORLs) are painful. This is fairly easy to demonstrate by touching one of these lesions with a dental probe or using the air spray attachment on a dental machine to blow air over the lesion. Most cat owners are not recognizing pain in their cats with these lesions. When the cats are treated for these lesions, usually by removal of the affected teeth, some owners, but not all, see a dramatic improvement in their cat's quality of life. The best explanation is that chronic pain has been alleviated. On the other hand, surgical extraction of teeth is painful and it is sometimes quite difficult, and therefore expensive, to remove these teeth because they break easily, leaving root fragments that must be carefully extracted. Often gum tissue grows over the weakened enamel and seems to provide protection from most of the pain. With all of this in mind, is it better to remove all affected teeth, or is it better to try to assess the cat's condition and remove the teeth only from cats who seem to need it or is it reasonable to ignore these lesions? Since general anesthesia is necessary to deal with this situation, would a cat make the choice to take the small risk of an anesthetic death in order to alleviate the pain or is something he or she would prefer to live with over having anesthesia? It would help a great deal if we could simply ask our patients, but we can't. So we make the best choices we can on an individual basis and hope they are correct.

My current goals are to recognize conditions that might be painful and to treat for the pain whenever it seems best to do that. A guideline that I use is to imagine if the condition would be painful if it was happening to me. I have had abdominal surgery so I can tell you that there is pain during the recovery period. So we dispense pain control medications for our surgery patients. I have talked to people who have had pancreatitis and they tell me the pain is severe so I try very hard to control pain in patients with this condition. If you think that a condition might be painful for your pet, pain relief is a good idea.

There are two broad categories of pain that are useful to think about because treatment options vary pretty significantly between them. Acute pain is suddenly occurring pain in response to an injury that disappears as the injury heals. Chronic pain is pain that persists after an injury has healed or that persists due to a damaging process that also persists, such as arthritis.

One of the interesting things about pain is that there seems to be a mechanism in the body for "remembering" pain -- events that were painful in the past may cause pain more easily the next time. In addition, some pain appears to become imprinted in the neurologic pathways and to persist even after an injury is healed. This is the one of the reasons that "phantom pain" associated with an amputated limb is believed to occur. Working towards decreasing these remembered and imprinted pain sensations has opened up a whole new area of research in pain relief.

Another interesting thing about pain is that it is a threshold event. I have always had a hard time explaining this concept to people. One way of looking at this is to think about how much more a second painful stimulus hurts when someone is standing on your foot. The pain from being stepped on caused enough discomfort to get near or possibly over the pain threshold and the second event gets a head start on causing pain because the nervous system is already at the pain threshold.

Another way of thinking about it is like a seesaw. You can put a rock on the high end of seesaw and it might not cause it to go down. If you add a second rock that might not move it, either. But eventually you will reach the point where the weight on the upper end suddenly causes the high end of the seesaw to fall. This is how pain threshold works. You really don't feel pain even though something has the potential to cause it until there is enough "weight" to tip over the pain threshold -- then you feel it suddenly.

The pain threshold has been demonstrated in good scientific studies to vary as much as fivefold between individuals who have a "low" pain threshold and those with a "high" pain threshold. This means that it takes five times as much pain stimulus to cause the people or pets at the high end of the spectrum to feel pain. There is nothing psychological about the difference to the best of researcher's ability to tell. Some animals and some people just have more sensitivity to pain. We see this routinely in our practice with the simple act of vaccinating pets. Some dogs and cats act as if the injection is severely painful every time and others don't even look back to see what we did. Knowing that there really is a big difference in how pain is perceived has helped me to give the pets who seem overly sensitive a break --- I just assume now that they really do feel pain more easily and that their complaints are justified.

The best way to deal with acute pain is to give pain relievers before it occurs. When this is done it can be demonstrated easily that lower doses of pain relief can control the pain and that the duration of need for pain relief is often shorter. This works well for situations in which pain can be anticipated, such as surgery, but it doesn't help much with pain that is due to an unexpected injury. When pain relievers must be given after an injury has occurred it sometimes takes much higher doses to tamp down the pain and get it under control. It is good to keep this in mind, because many people make the mistake of using low doses of pain reliever initially, hoping they will work. It is probably better to start with high doses and then to cut the dosage if it becomes apparent that lower dosages will work.

There are a number of available options for acute pain relief in dogs. There are fewer options in cats but there has been some progress in obtaining pain relief for this species over the last few years.

I am going to try to give the basic facts for a number of pain relief medications in the remainder of this month's VetInfo Digest. I am going to stick to pain relief medications that can be given at home. There are a number of additional pain relief medications that can be used in hospital situations in which intravenous use or injections of pain relief medications is possible. This is a field that is also rapidly expanding and your vet should be able to provide good pain relief for a pet in the hospital situation.

Remember when reviewing the following listing of medications that no veterinarian is likely to be familiar with all of them and some may be impractical for most pet owners. It is my intention to show that there are a variety of possibilities for achieving pain relief and often several possible medications in each pain relief category. It is usually possible to find some way to control pain with medications in most patients but there are some situations in which pain control is extremely difficult to achieve without surgery (such as amputation of a leg for relief of pain from bone cancer) or advanced pain control measures (such as alcohol blocks of individual nerves, permanently disabling them).

Nonsteroidal anti-inflammatories (NSAIDs)

The nonsteroidal anti-inflammatory medications are the mainstay of pain relief in dogs. Unfortunately, cats do not tolerate this group of medications very well, with a few exceptions. Many clients view NSAID medications as safe, based on the fact that many of them are over-the-counter medications for human use. Despite this general feeling of safety it should be noted that aspirin alone is suspected of causing approximately 16,000 deaths per year in the United States due primarily to gastric or intestinal ulcers. This group of medications is safer in many respects than other classes of pain relief medication but they are not entirely risk free. NSAIDs are frequently used for both acute and chronic pain.

Older NSAIDs such as aspirin, ibuprofen, ketoprofen and naproxen are more likely to cause ulcers than newer medications, referred to as "Cox2 inhibitors". On the other hand, when the Cox-2 inhibitors cause problems they can be more severe. So there is kind of a tradeoff between fewer side effects and more severe side effects. There is some controversy over whether the newer drugs actually provide more pain relief than the older ones. I definitely fall in the camp who believes that the Cox-2 inhibitors are more effective pain relievers for chronic pain.

It is very important to stop administering any NSAID and to call your vet if your pet stops eating or even has a significant decrease in appetite while the medication is being used. It is also quite important to let your vet know if you are using an over the counter pain relief medication at the time of yearly visits and especially when your vet is prescribing a medication for another purpose. Medications do interact and your vet must know that a medication is being given in order to take interactions into account.

There are a number of NSAIDS available for use in dogs and cats (and some common ones that shouldn't be used):

Aspirin: The recommended dosage for aspirin in dogs is 10mg/lb of body weight every 12 hours. The recommended dosage of aspirin for cats is controversial but a good starting point is 10mg/lb of body weight every 48 to 72 hours. Aspirin has a very long half life in cats and it is very easy to overdose a cat if aspirin is given on a daily basis. It is best to use aspirin under the supervision of your vet when using it in cats.

Ibuprofen (Motrin tm, Advil tm, others): it is generally agreed that the risk of gastrointestinal ulceration is high enough with this medication that its use is not advisable in either dogs or cats. In at least one study 100% of dogs given ibuprofen for a week developed gastrointestinal ulceration detectable by endoscopy. Despite this I have had a number of clients tell me they were using ibuprofen without visible ill effect, so if you happen to be doing this don't panic, but do switch to an alternative medication.

Ketoprofen ( Orudis KT tm): The recommended dosage of ketoprofen for dogs is 1mg/kg every 24 hours. Some texts advise using this for no more than 5 days. If a longer dosing period is necessary using 0.5mg/kg once a day may be safer and still effective. Ketoprofen may be used with great caution in cats at the same dosage but it is hard to do this practically, since the tablets are 10mg in size, which is the dosage for a 22 lb. cat or dog.

Naproxen (Aleve tm): The published dosage for dogs is 1.1 to 2.2mg/kg given once a day or every other day. Naproxen is not recommended for use in cats. Despite the existence of a published dosage we have seen ulcers in three dogs associated with the use of naproxen by pet owners. While none of them seemed very clear about the dose they were using this has caused us enough concern that we feel that naproxen should not be used in dogs or cats.

Etodolac ( Lodine Rx, Etogesic Rx): is approved for use in dogs. It provides good pain relief for long term conditions but has a tendency to cause a decrease in tear production which can be a really severe side effect. For this reason, it is very important to watch for any signs of eye pain or discomfort when using etodolac long term and to discontinue use if these problems develop. The recommended dosage in dogs is 10 to 15mg/kg once a day. Etodolac should not be used in cats.

Tolfenamic acid: is approved for use as a pain reliever in Europe and Canada but not in the U.S. It is dosed on an unusual schedule requiring three days of dosing followed by four days without medication, which is very important to follow. It is used in both dogs and cats. The recommended dosage is 4mg/kg or less once daily for 3 days, repeating the dosage after a 4 day rest if necessary to use chronically.

Piroxicam (Feldene Rx): is a potent NSAID that has some unusual benefits for certain conditions. It can be used solely for its pain relieving capability but since it is more likely than most NSAIDs to cause gastrointestinal ulceration its use is usually reserved for conditions in which it's other benefits are more meaningful. The recommended dosage is 0.3mg/kg every 48 hours (can be used every 24 hours for the first two doses). In cats it is sometimes used at 72 hour intervals rather than 48 hour intervals. Piroxicam has the ability to dramatically shrink some forms of cancer, especially transitional cell carcinomas of the urinary bladder. It also seems to help with severe bladder inflammation associated with chronic cystitis. There is some evidence that piroxicam is also effective for shrinking nasal tumors and reducing discomfort associated with this type of tumor. It may be best to administer misoprostol, a gastrointestinal protectant, when using piroxicam.

Meloxicam (Metacam Rx): The recommended dosage in dogs is 0.2mg/kg on the first day, then 0.1mg/kg every 24 hours. There is a measured dosing syringe for the liquid form of this medication. Meloxicam is generally regarded to have more of a Cox-2 spectrum in its action. It is available as a honey flavored liquid or in tablets. Meloxicam is only approved for use in dogs in the United States but it has been studied for use in cats and seems to be reasonably safe. The recommended dosage for cats is 0.1mg/kg once a day for 5 days, then 1 drop from the standard dispensing bottle for chronic use. Our experience has been that meloxicam works well at the higher initial dosage but doesn't seem to work nearly as well for chronic pain if the lower long term dosing schedule is used. This may or may not be a typical experience.

Deracoxib (Deramaxx Rx): The recommended dosage for dogs for acute pain is 3 to 4mg/kg/day. For chronic pain the dosage is 1 to 2mg/kg/day. This is a Cox-2 inhibitor. Based on our clinical experience this is the most potent of the NSAID pain relievers, on the average. There are individual variations among patients, though. There have been some reports of sudden severe gastrointestinal bleeding associated with the use of deracoxib, which is similar to the experience with Cox-2 inhibitors in people. This medication is not recommended for use in cats.

Carprofen ( Rimadyl Rx): The recommended dosage for dogs is 1mg/lb every 12 hours or 2mg/lb every 24 hours. In chronic pain situations it is often possible to use 1mg/lb per day successfully, although this does vary from dog to dog. This is a predominantly Cox-2 inhibitor. There are confirmed cases of liver failure associated with the use of carprofen (considered to be a rare complication), so it is best to check blood work for liver damage prior to use and to recheck lab work after 2 to 4 weeks of use. Carprofen is not approved for use in cats but it is sometimes used on a one time basis for pain relief associated with surgeries such as spay or neuter procedures.

Tepoxalin (Zubrin Rx): The recommended dosage of tepoxalin in dogs is 10mg/kg once a day. This medication suppresses both Cox-1 and Cox-2 systems. Tepoxalin is not approved for use in cats and I have not seen a published dosage to use in this species. Zubrin is the most recent of the primarily Cox-2 NSAIDs to gain approval and we have not used it as the others have been working well. I suspect that this medication works just as well as the others, though.

Narcotics

Narcotic pain relief medications have been used for a very long time. There are a number of these medications available with a wide variation in their pain relieving capability and in their potential for addiction. Fortunately, in veterinary medicine, addiction is much less of a problem than in human medicine for the simple reason that dogs and cats can't buy the medications themselves. It is still important to recognize that it can occur and to withdraw medications appropriately when there is a reasonable expectation that some degree of addiction may be present. Narcotic medications work well with other pain relief medications, especially the NSAIDs and combinations of these medications work better than either group alone. There are categories of narcotics and some of them work in ways that make it a bad idea to use one right after another or to use two antagonistic narcotics at the same time. This is mostly a worry for your veterinarian when prescribing narcotics but it is important not to use these medications without the advice and supervision of a veterinarian.

Narcotic medications are almost all controlled substances, meaning that they are regulated by the Drug Enforcement Agency (DEA) as well as the Food and Drug Administration (FDA). Veterinarians have to purchase and maintain special licenses to use these drugs and must account for every instance in which they are used. When it becomes common knowledge that a veterinary practice uses and stores narcotics there is a higher risk of robberies for the clinic. Due to these issues there are veterinarians who will not stock and use narcotic medications. In general it is possible to practice without narcotics but in many instances it severely restricts the ability to properly treat a patient's pain. While I can really understand why veterinarians would want to avoid the use of this category of medications I also think they are important enough in the treatment of painful conditions that it is worth finding a veterinarian who is willing to put up with the paperwork and minor risks of handling these medications if your pet has a painful condition that won't respond to drugs that are not controlled substances.

Morphine is the narcotic most people are most familiar with. It is a very good pain relief medication and it is definitely worth considering when a pet has severe pain. Morphine works consistently and reliably in dogs. It sometimes causes pretty severe reactions in cats in which extreme excitability occurs. This can be a major problem if the cat's condition can be worsened by uncontrolled activity, such as a cat recovering from orthopedic surgery. One drawback of morphine is that it must be administered frequently. The dosage for dogs is 0.5 to 2mg/kg every 6 hours. Cats are usually dosed at 0.2 to 0.5mg/kg every 6 to 8 hours. Morphine frequently causes vomiting and can produce sedation. At higher doses constipation can be a problem with long term use. There are sustained release morphine preparations that work well in dogs but which are much more expensive and are closely monitored by pharmacies, making it uncomfortable for pet owners who have to purchase these medications, at times. If your pet needs pain relief and it is only possible to give medications twice a day these are worth considering, despite the hassle.

Outside of the United States one of the most commonly prescribed narcotics is pethidine, which is generally known in the U.S. as meperidine (Demerol Rx). In the U.S. the use of meperidine is less frequent, which may be due to relative availability as meperidine is a controlled substance in the U.S. There is some question about the duration of action of meperidine in dogs and cats as most studies suggest that it provides approximately one to two hours of pain relief. It is supposed to work well in combination with NSAIDS and this effect may be due to good short term pain relief. In many cases if severe pain can be dampened, even for a short time, it will make pain easier to control over the long term. The usual dosage is 2 to 5mg/kg for cats and 2 to 10mg/kg for dogs but recommended dosing intervals vary from "as needed" to three times a day.

Codeine and hydrocodone are used frequently in veterinary medicine. These are not nearly as potent for pain relief as morphine but they make a very good combination medication for use with NSAIDS. Vicodin (Rx) is a mixture of hydrocodone and acetaminophen, which can be used safely in dogs. Codeine/aspirin combinations are also available. These combinations are not acceptable for use in cats. We usually base our dosing on the hydrocodone or codeine portion for combination medications. Hydrocodone is dosed at 0.2 to 1mg/kg every 6 to 8 hours in dogs. Hydrocodone can be used in cats if it is the sole ingredient, usually 2 to 5mg per cat once a day. For pain codeine is dosed at 1 to 4mg/kg every 6 to 12 hours in dogs. I am not aware of a published dosage for cats.

It is pretty common in veterinary medicine to dispense butorphanol (Torbutrol Rx) for pain relief, especially in cats. While this is definitely better than no pain relief at all there are limits to the effectiveness of butophanol for chronic pain, as its effects only last for one to two hours in most dogs and several hours in cats. In addition, increasing the dosage of this medication can sometimes lessen its pain relieving effects rather than increase them. Butorphanol is usually dosed at 0.1mg to 0.5mg/kg for pain relief.

Buprenorphine is a narcotic that is not approved for use in dogs or cats even though it is used fairly often. It provides a longer duration of pain relief than butorphanol. It doesn't come in an oral form but the injectable form is given orally in cats as it is tasteless and works well as an oral solution. The usual dosage is 0.01 to 0.02mg/kg every 8 to 12 hours. This medication is rapidly gaining favor in the United States as the preferred narcotic for use in cats.

Fentanyl is usually used as a transdermal patch (Duragesic Rx) in dogs and cats. It provides long term pain relief by constant absorption through the skin from the patch. It is surprising, but most pets will leave these patches alone. Despite this it is important to prevent the pet from ingesting the patch as this can provide an oral dosage high enough to cause coma or death. It is important to recognize that there is a delayed onset of effect when using the patches. In dogs it takes about 12 hours to achieve good pain relieving dosages and in cats it takes a minimum of five hours. The effective life of the patch is about 3 days in dogs and up to 5 days in cats. The pain relief from these patches is considered to be moderate, especially in dogs. For this reason it is often necessary to use them as a constant provider of pain control but to supplement them as necessary with a compatible narcotic or an NSAID.

Other Pain Relief Medications

Tramadol (Ultram Rx) is a a pain relief medication that has similar effects to narcotics but is not actually a narcotic compound. It is useful in both dogs and cats for long term pain relief. This is a medication that can be used by veterinarians who are adverse to using controlled substances but who wish to provide some benefits associated with narcotics. The recommended dosage in dogs is 1 to 2mg/kg every 12 hours but doses up to 5mg/kg and dosing intervals as short as every 6 hours have been used when necessary in dogs without major reported adverse effects. In cats the recommended dosage is usually 1/4th of a 50mg tablet per cat every 12 hours.

Acetaminophen (Tylenol tm): cats can not process acetaminophen at all and it is unsafe in cats at any dose. Dogs tolerate acetaminophen without problems at dosages up to about 25mg/lb every 8 hours but there is a lot of controversy over how well this medication works in dogs. Most veterinary pharmacologists seem to suspect that it doesn't work at all. It is often given in combination with hydrocodone as the combination medication is less expensive than hydrocodone alone.

Gabapentin (Neurotin Rx): is a seizure control medication that seems to suppress chronic pain. It is expensive and we have not had a situation in which we had to use it so I have no personal experience with it. The recommended dosage is 1 to 4mg/kg every 12 hours in dogs and every 24 hours in cats. In humans gabapentin is reported to provide additional pain relief in extreme pain situations in which narcotics such as morphine aren't potent enough alone.

Antidepressants
It might sound strange to include antidepressants in the pain relief category of medications but there is reasonable evidence that some of these medications do help to relieve chronic pain. It is plausible that some of the antidepressant effect may in fact be pain relief, at least in some patients.

The antidepressant that is most commonly used as an aid in controlling long term pain is amitriptyline (Elavil Rx). This medication has been used for some time in pets as an aid in controlling behavioral problems, for its antihistamine effect in skin disease and now for chronic pain relief. It is used in combination with pain relief medications in almost all cases and it seems to reduce the amount of pain relief necessary in many patients. In dogs amitriptyline is usually dosed at 1 to 2mg/kg every 12 hours. In cats the dose is usually 2.5 to 12.5mg per cat given once a day, usually at night.

Imipramine (Tofranil Rx) is another antidepressant that seems to help with chronic pain. In dogs it is generally dosed as 0.5 to 1mg/kg every 8 hours. In cats the dose is 2.5 to 5 mg/kg every 12 hours. We have no clinical experience with imipramine for pain but we have used it in dogs for urinary incontinence and one of those owners noticed that her aging Lab was more mobile while on this medication.

Acupuncture

Acupuncture seems to work well for some patients for relief of both acute and chronic pain. In studies somewhere between 50% and 90% of patients who have acupuncture still need additional pain relief but less potent medications can sometimes be used or lower doses of stronger medications. There is some concern that a tolerance to acupuncture may occur in chronic pain where it is necessary to repeat treatments regularly and that owners might miss this if they are not looking for it. Acupuncture is not available everywhere but it is an option to consider when pain is not responding well to medications or when medications are undesirable for some reason, such as an adverse effect on disease conditions already present.

Corticosteroids

Most veterinarians and veterinary clients don't view corticosteroids as pain relief medications, for the primary reason that they provide very little actual pain relief. On the other hand, they are the most potent anti-inflammatory medications available and often it is inflammation that is causing the pain in the first place. Corticosteroids have a great number of side effects, including weakening cartilage in joints. However, there is a time in arthritis when there really isn't much reason to worry about cartilage in the joints anymore because it is already severely damaged. This is also often the time when a pet owner is considering euthanasia because a pet isn't getting around well enough to enjoy life at all. Using corticosteroids at this time makes sense. After all, if the alternative is euthanasia, what side effect will change that scenario?

Pain Relief Without Medications

For pain caused by arthritis and back pain there is good evidence that weight reduction to ideal or even slightly below ideal weight for the dog's size will lessen chronic pain quite a bit. In some studies weight control has worked as well as the NSAIDs for control of chronic pain from these types of conditions. It can be hard to get your pet to lose weight but the benefits are definitely worthwhile.

Don't overlook the value of simple touch and of caring compassionately for pets experiencing pain. It really does help to massage chronically sore limbs. Ice packs can be very helpful for some types of surgical pain and for acute injuries both in limiting pain and speeding the healing process. Warm compresses can help with chronic pain, especially arthritis pain. It can take some coaxing to get a pet to accept these types of care but it is often worth the effort. A soft bed seems to help some dogs with hip dysplasia or elbow dysplasia quite a bit, although it is important that it still be thin enough that they can get up easily from it. Just showing a pet sympathy can help a great deal with acute pain and probably works pretty well for chronic pain, as well.

Corrections:

Two months ago I said that the new formula of Pepto-Bismal (tm) contained salicylates and might be toxic to cats in high doses. I meant to say the new formula of Kao-Pectate (tm).

Last month I reversed the figures for heartworm prevention -- ivermectin and milbemycin are effective at least 90% of the time and are probably effective closer to 99% of the time if used according to directions.

Thanks for your Support!

The VetInfo Digest is published by:

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P.O. Box 476

Cobbs Creek, VA 23035.

The opinions expressed in this newsletter are those of Michael Richards, DVM., author.