VetInfo Digest

VetInfo Digest February 2007

Table of Contents:

Slentrol ™

Vaccine for Periodontal Disease

Vaccine Recommendations for Cats

IverHart Max ™

Xylitol Poisoning in Dogs

Flea and Tick Control, revisited

This Month’s Note:

Henry is doing his best to distract me right now. He is carrying around a slipper that he probably knows he shouldn't have and bringing it by my feet every now and then, just to be sure that I notice him. Lately I have been stopping what I am doing and playing with him quite a bit, which is why there is no time to do that tonight. Despite that, I'm going to give in and play with him for a few minutes, very soon. He knows it. I know it. I guess it is part of the reason that we have pets. So if this issue of the VetInfo Digest comes a day or so late, or arrives unedited, remember that it’s my dog's fault!

There are a number of new veterinary products coming onto the market soon. There is information available on some of these products now. At least one of these products, Slentrol ™ , is generating a lot of publicity. While all the information currently available is preliminary, it may be helpful to get some idea of what all the hype is about.

Slentrol

Dirlotapide (Slentrol Rx) was approved by the FDA for use in dogs to aid in weight management last month. It is not currently available from the manufacturer, Pfizer, and the only information available on the medication comes from the FDA Freedom of Information Act site. If you would like to read the entire study the URL for this site is www.fda.gov/OHRMS/DOCKETS/98fr/2006-141-260-fois001.pdf.

Dirlotapide will be available as a liquid medication meant to be added to the food. It is a "selective microsomal triglyceride transfer protein inhibitor that blocks the assembly and release of lipoprotein particles into the bloodstream", according to the package insert. It causes vomiting or diarrhea in about 25% of dogs treated with it, according to the studies cited in the FDA application, although for most dogs these episodes are transient. One dog in the study developed liver disease. It is unclear due to the small number of dogs tested whether this was due to the medication but it is something that has to be considered when contemplating its use. Dirlotapide is not recommended for use in dogs on long term corticosteroid therapy or who have pre-existing liver disease.

The restriction against using it in dogs who are on corticosteroid therapy is perhaps the most disappointing part of the package insert, as these are the dogs who really do need help with weight and appetite control, as the corticosteroids increase appetite and fat deposition. Hopefully, as time goes on it may become clear that it is reasonable to use dirlotapide in a dogs who are on corticosteroids.

Based on the studies presented in the application dirlotapide does look like it will probably work as an aid in weight control. Even dogs who had food available at all times lost weight in the studies. The dosage of the medication is adjusted to keep the weight loss gradual and it is necessary to monitor the weight loss to properly adjust the dosage. This means that it will be necessary to bring the dog to the veterinarians on a regular basis while using dirlotapide.

Philosophically, this is a really unusual drug. It is a treatment for the dog's owner's inability to restrict the diet for the pet. Sort of a once removed treatment aid for obesity. There is no question that most obese dogs live in environments in which their food intake is mostly, or completely, controlled by their owners. Therefore the simplest approach to weight control is simply to feed less. This is accomplished most easily by measuring the amount of food given and reducing that amount. The measuring part is the key. Using a giant drink cup to measure the food and eyeballing "about a half of a cup" is not the same as using a real measuring cup and feeding a set amount, like one cup twice a day. Interestingly, in the studies presented, the dogs in the placebo group lost weight during the studies, as well. This is a frequent finding in studies like this, in which people are asked to monitor a problem with their pets on a regular basis. The added attention to the problem often seems to result in improvement, even without medication. This just adds a little weight to the argument that most people can manage their pet's weight, at least to some degree, when a sincere effort is made to do so.

Some pet owners really do seem to be incapable of controlling the amount they feed their pets. Truthfully, I even mess up on this count at times, as I like to give my dogs more treats than I should. I keep reasonably good control of the total calories by cutting back on regular food to match the caloric intake of the treats, though. Using a medications isn't as good as practicing self control for the owner and quantity of food control for the pet, but it is an option. It is still questionable to me whether it is good medical practice to put a pet on a medication with the potential for side effects when there is a way to deal with their weight control problems that doesn't involve a risk of side effects but I know from experience that it may be the only way to control weight for some pets.

The other issue that I suspect may be a problem with dirlotapide is a temptation on the part of people to take the drug themselves in the hope of losing weight easily. Due to the cross-over in usefulness of drugs for people and pets, it is easy to assume that if a medication is safe for pets it will probably be safe for humans. In the case of this particular medication, one effect noted in the studies in dogs should preclude that presumption in the case of dirlotapide. In the studies cited it was noted that dirlotapide lowered high density lipid levels in the dogs in the studies. Since the high density lipids (HDLs) are the ones thought to be protective against heart disease, in contrast to low density lipids (LDLs), this could be a really serious side effect in humans. Dogs, with the exception of doberman pinschers, do not normally develop atherosclerosis. This makes the changes in lipid levels less likely to be a problem. It would be scientifically interesting if the changes in lipid makeup in dogs caused heart disease, but hopefully that won't happen.

Vaccine to Prevent Periodontal Disease

Dental care for pets lags far behind dental care for humans, at least on the average. It is possible to brush some pet's teeth without much resistance from the pet but for most pets twice daily tooth brushing is a goal that is never achieved. Thorough teeth cleaning is really impossible to do in dogs who are not anesthetized as there is no reliable way to get a dog to open its mouth and hold it open while the inside of the teeth are examined and cleaned. It is possible to do a reasonably good job of teeth cleaning in cats without anesthesia since cats have fewer teeth and less problem with tartar accumulation on the inside of the teeth but even in cats a much better job of cleaning and examination can be done with anesthesia. Unfortunately, anesthesia is not completely safe and it also adds significantly to the cost of teeth cleaning. So most pets do not get either routine dental care or intermittent regular teeth cleaning sufficient to really control periodontal disease. This has prompted a search for easier ways to clean teeth and other ways to prevent periodontal disease. Recently, a vaccine has been approved, on a provisional basis by the USDA, for use in dogs as an aid in controlling periodontal disease.

Porphyromonas Vaccine helps to control the anaerobic bacterial population that is mostly responsible for infection under the gums and that is the biggest contributor to bone loss around tooth roots. It does not control the aerobic bacteria that are most responsible for tartar production. Therefore, it is a vaccine that contributes to the overall care of teeth but doesn't replace regular dental care.

It is always hard to figure out if the potential risks associated with vaccination justify the use of the vaccine in a particular pet. This is going to be a particularly difficult problem when considering the use of Porphyromonas Vaccine. Approximately 85% of dogs over three years of age have either gingivitis or periodontal disease. It would be reasonable given this situation to consider vaccination of all dogs since the vaccine has the best chance of helping when used as a preventative measure. However, the vaccine has been studied in only a limited population, so far, and it is not possible to be certain that there will not be problems with vaccine side effects in the larger population at this time, despite a good safety record (as reported by Pfizer, the manufacturer) in clinical trials to date. This vaccine is actually a bacterin, or a vaccine made to prevent bacterial infection. In most cases bacterins do not provide immunity for as long as vaccines made to prevent viral infections so it is likely that booster vaccination will be required at least annually and possibly as often as twice a year. At this time the manufacturer does not appear to be making a specific recommendation for frequency of booster immunizations.

The vaccine may be given to puppies as young as seven weeks of age. Obviously, no one can predict at this age with any certainty which individual dogs would require it in the future when it is given to puppies this young. Despite this, there are certain breeds in which periodontal disease is so likely that it may make sense to start the vaccine early and continue to give booster vaccinations over the lifetime of the dog. Among the breeds that are highly likely to develop periodontal disease, greyhounds, hunting hound breeds, miniature poodles and dachshunds immediately come to mind.

The development of periodontal disease follows a path that usually starts with tartar (calculus) formation on the teeth, progresses to gum inflammation (gingivitis) and then to periodontal disease. With this in mind it wouldn't be too hard to evaluate the risk for development of periodontal disease in an individual dog. If a dog's teeth stay very clean and its gumline is sharp and uninflamed then it is unlikely that dog will go on to develop periodontal disease, making vaccination for it unnecessary. On the other hand, a dog who has tartar by the time he is eight months old or who has gingivitis visible during a physical exam when he is one or two years of age is very likely to go on and develop periodontal disease. This dog would be a good candidate for vaccination with Porphyromonas Vaccine.

Regardless of whether or not a dog is vaccinated against periodontal disease it is still necessary to continue with regular dental care to the extent that it is possible to do so. Teeth cleaning is still important on a regular basis. It may be possible to extend the time between cleanings some due to vaccination but it will not be advisable to ignore calculus accumulation on the teeth altogether.

It is going to take some time to determine the best use of Porhyromonas Vaccine. Like most products that make it to the market, real world use among a bigger population of dogs will bring any significant problems with the use of the vaccine to the surface over time. For dogs who have a known tendency towards periodontal disease already the choice whether to use the vaccine or not may be easier, as the long term risk to overall health from periodontal disease would justify taking the small risk of a vaccine reaction. This vaccine should be available to veterinarians soon and is something to watch for if your dog has problems with periodontal disease.

Vaccine Recommendations for Cats

In the past I have recommended giving one dose of modified live vaccine to cats when giving the RCP (rhinotracheitis, calicivirus, panleukopenia) vaccine to cats. This is also sometimes referred to by other names, such as feline distemper (for the panleukopenia portion) or feline herpes virus (for the rhinotracheitis) vaccine. The new guidelines from the American Association of Feline Practitioners (AAFP) strongly recommends giving at least two doses of the RCP vaccine during the initial vaccination series. Their recommendation is to start giving the vaccine at 6 to 8 weeks of age and to give it every 3 to 4 weeks until the kitten receives one of the vaccinations at 16 weeks of age or older.

I really do not like to give the kitten or puppy series of vaccinations more frequently than once every 3 weeks but the AAFP research suggests that any interval longer than 2 weeks apart is acceptable. The only circumstance in which it would make much sense to vaccinate every 2 weeks that I can think of would be cats in a shelter or densely populated cattery. A kitten in a home by itself or with less than 5 other housemates is pretty unlikely to be exposed to any of these viruses on a consistent enough basis to require vaccination as frequently as every 2 weeks.

There is now a vaccine available from Ft. Dodge Animal Health to prevent infection with the new more virulent strain of calcivirus that has been causing outbreaks of fatal infection with calicivirus. This problem started on the West Coast but has been moving eastward with pockets of outbreaks. It is a very deadly virus which seems to have limited its spread to some degree, since most infected cats die quickly. While this virus is not a huge threat to most cats it is definitely worth considering for cats who travel a lot, are boarded frequently or who are taken to cat shows or other places where cats gather. The vaccine is available as a stand-alone vaccine or in combination with the traditional RCP vaccine.

Iverhart Max ™ , monthly heartworm, roundworm, hookworm and tapeworm prevention

We have a few dogs in our practice who seem to get tapeworms over and over again. Dogs and cats acquire tapeworms in several ways, but primarily from ingesting fleas, rabbits or small rodents. The species of tapeworm that is acquired by eating fleas, Dipylidium caninum, is thought to be the most common tapeworm species affecting dogs and cats. The most common species of tapeworm acquired by eating rabbits is Taenia pisiformis. Ingesting rodents is a way of acquiring several species of tapeworms, including Spirometra mansonoides and Taenia taeniaformis.

It seems like it would be relatively easy to eliminate Dipylidium caninum tapeworms by controlling the flea population but this doesn't always work. We have some clients who seem to be achieving very good flea control whose pets still seem to get Dipylidium tapeworms fairly frequently. Our assumption is that these pets are exposed to a flea source, such as a neighborhood pet and acquire fleas just long enough to become infected by tapeworms as they pick the flea off themselves, even though overall flea prevention is good.

We also have a number of pets in our rural practice who have access to rodents and rabbits and who therefore acquire frequent tapeworm infestations in this manner. Most of our clients whose pets have access to the outdoors unsupervised are reluctant to limit the pet's freedom. Without doing that, there is no way to prevent tapeworm reinfestation.

When we have a pet who constantly has tapeworm infestations we usually just choose an interval everyone is comfortable with to give medications that kill tapeworms. In most cases this has been every two to three months but there is no reason I know of not to give the medication more frequently if desired. Tapeworms are generally well adapted parasites, meaning that they cause little harm, but most of our clients still want them treated since they are one of the few worms people see on a regular basis and people seem to have an aversion to seeing the tapeworm segments. The pharmaceutical companies seem to have grasped this strong aversion in their pricing, as tapeworm killing medications have consistently cost more than other deworming medications. However, with the introduction of the Iverhart Max, a heartworm prevention medication that also has ingredients to kill roundworms, hookworms and tapeworms, this situation may be changing.

Iverhart Max is only approved for dogs but I know of no reason that it couldn't be used for cats. For dogs who constantly have tapeworm infestations using this combination dewormer monthly should control tapeworms reasonably well with a tablet that is fairly easy to administer. In addition, the pricing of the medication is low enough that it competes well with tapeworm medications alone. For cats, even though the medication is not approved in this form (it is approved in other forms for cats), it is in a form that is likely to be easier to administer than the currently available tapeworm medications approved for cats, since Iverhart is a flavored chewable tablet that could be crushed and mixed with food. In addition to this, the cost of Iverhart Max is about the same cost per tablet at the other medications available to kill tapeworms.

I think that Iverhart Max may be worthwhile to consider for dogs who are used for hunting purposes or who have the ability to scavenge or hunt without supervision at times. There is a species of tapeworm, Echinococcus, for which dogs are a host that is contagious to humans. This species of tapeworm can be fatal in humans and it makes sense to limit exposure to it when it is possible to do so. Using a once monthly heartworm prevention product that also kills tapeworms would be a fairly effective way to do this.

Xylitol poisoning in dogs

While dirlotapide seems reasonably safe for dogs but not so safe for people, the exact opposite situation exists for xylitol. You may recognize xylitol as an ingredient in sugar-free gum or in toothpaste. It is also used to aid people who need sugar substitutes due to diabetes or when a low carbohydrate diet is advisable. There are a number of baked goods available now with xylitol as a sugar substitute. Xylitol is also available for use in home baking. In people, xylitol seems safe. It can be toxic to dogs in quantities that many dogs will readily ingest, though. Dogs have died from xylitol poisoning after eating as little as five or six cookies or 30 pieces of gum ( Dunayer, et all, JAVMA, 2006). For those of you who own dachshunds, you know that 30 pieces of gum is just a start for a dachshund.

Xylitol has two harmful effects in dogs. Many dogs who ingest xylitol will experience an episode of hypoglycemia (low blood sugar) if they ingest more than 0.1gm/kg of xylitol in a single dose. Since there are 190 grams of xylitol in a cup of the granulated sugar substitute and about 0.3gm or more per stick of gum, it is easy for dogs to get this much xylitol (Dunayer, Veterinary Medicine, Dec. 2006). If you know that your dog has ingested xylitol, baked goods containing xylitol or sugar-free gum, it would be a good idea to contact your vet and to consider monitoring for, or treating for, hypoglycemia.

Of even more concern is a recently discovered tendency for xylitol to cause acute liver failure in some dogs. This effect appears to be dose related, although that is not certain, yet. If your dog ingests more than 0.5gm/kg of xylitol in any form it is very important to contact your vet or to go to an emergency veterinary center if your primary care veterinarian is not available. There is no specific antidote for xylitol poisoning so treatment is aimed at preventing liver damage by using anti-oxidant therapy, controlling blood glucose levels and monitoring for severe complications such as blood coagulation disorders associated with acute liver failure. Supportive care is worth trying but some dogs will die despite therapy.

Since xylitol is found in many foods that seem to be beneficial for people it is easy to imagine a pet owner giving a dog a product containing xylitol without even thinking of the potential for toxicity. If your pet experience unexplained hypoglycemia or acute liver failure it is important to keep this possibility in mind.

At this time there does not appear to be adverse effects when cats ingest xylitol, other than the possibility of diarrhea if sufficient quantities are ingested.

Flea and Tick Control revisited

Dr. Michael Dryden, one of the most prominent flea and tick researchers, recommends making some changes to the flea and tick control programs that most veterinary clients use. The really effective flea and tick control products are expensive compared to the older generations of flea control products. For this reason, most of my clients choose one product and use it exclusively. Dr. Dryden believes that this approach is likely to lead to resistance to the newer flea and tick products more quickly than it would otherwise occur.

His recommendation is to use one of the topical products that kills fleas well, such as fipronil (Frontline Topspot ™), selamectin (Revolution Rx) or imidocloprid (Advantage ™ ) but also to use a product that controls flea reproduction. Methoprene ( Precor ™ ), pyriproxfen (Nylar ™ ) or lufenuron (Program Rx, Sentinel Rx) suppress flea reproduction. Lufenuron is an oral medication and the other two products are available in a number of forms, including topical spot-ons, sprays and collars.

There is some worry among veterinarians at the present time that resistance to fipronil is occurring in flea populations where the product has been used extensively. At the present time this information is anecdotal and I am not aware of any published reports that document resistance. Despite this, we are somewhat suspicious in our practice that this may be occurring. Most of the time when people tell us that Frontline ™ isn’t working for their pets we discover that they aren’t using it once a month, aren’t using it properly or are buying products over-the-counter that have similar names or appearances but aren’t really Frontline or aren’t treating all the pets in the household. We do have a few clients who at least buy sufficient amounts of Frontline ™ to provide monthly dosing for all their pets who still have flea control problems, though. If you have been using Frontline and you suspect that it isn’t working well there isn’t a product currently available that controls both fleas and ticks as well as Frontline has in the past, but it is possible to get the same effect by daily tick removal or by using Advantix ™

For several years now it has been possible for most of our patients to be flea free by treating them topically with the newer flea control products without having to treat the house or other environments the pets occupy. It has always been possible to gain control of a flea infestation by treating the pet’s environment but it didn’t seem to be essential. In some cases now we have had to go back to this recommendation to get good flea control. This seems to be due to the unusually warm winters in our area, so it may not be true in all areas of the country.

Dr. Dryden recommends year round flea control. This is something that we have not recommended in the past in our area but which we also have found to be necessary in the last couple of years. This is especially true for our patients who have flea allergy dermatitis. The adult flea population has made it through the winter pretty well in Virginia the last two years and for pets who are miserable after as little as one flea bite, continuing flea control has been a necessity.

It was nice for a few years when fipronil and imidocloprid first came out. Flea control went from very difficult to fairly easy for most veterinary clients to handle. There is some hope for a return to those times, at least temporarily, as a new flea and tick product is supposed to be coming on the market soon. Unfortunately, despite my best efforts, I don’t know anything about this product yet. With some luck it will be as effective as Frontline and Advantage were when they first arrived on the market. If so, rotating between the new product and one of the older products, as well as adding a flea reproduction inhibitor, might give the new product the change to be effective for a longer period of time.

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