VetInfo Digest    September 2000

 

This Month:

ODDS and ENDS

Phosphate Binders

West Nile Virus

EEE

Losing Toe Nails

Spironolactone

Vaccine Associated Sarcomas

Mammary Tumors

Asthma in Cats

Adverse Drug Reaction Reports

Melanoma Vaccine

Seizure Control in Pets

Out of Time

September Note

I have always answered questions from subscribers in the order in which they were received. I have done this because I do not wish to miss any questions and it was easiest to keep track of them if I just went through them one by one. However, some questions take as long as two or three hours of research to answer and others take only a minute or two but may be quite important. As our subscription rate has increased, there have been times recently when it has taken me almost a week to get to some questions. I have decided that I am going to have to prioritize the mail, answering the easier questions first and researching the more difficult ones as I can. It is still my intention to try to answer all subscriber questions and to try to do it in a timely manner. I anticipate that there will be some problems as we switch to a system of trying to sort the mail before answering it. Please continue to let us know if you do not receive a response within 3 to 5 days

Odds and Ends

There are always a few small tidbits of information that we run across during a month that seem like they would be good to pass on, but which don't really merit a separate article. This month, I have collected several of these items and have put them together in the "Odds and Ends" section.

Dogs and Cats with Kidney Disease and High Phosphorous Levels

Phosphate binding agents are often recommended for dogs and cats with chronic renal failure in order to control phosphorous levels in the body. Amphogel (tm) was the recommended product to use, but this has gotten hard to find. Aluminum hydroxide, the active ingredient, is available as a generic product, though. Your pharmacist should be able to get this for you, if phosphate binders have been recommended. The dosage is 30 to 90mg/kg/day, adjusted based on serum phosphorous levels. Phosphate binders must be mixed with the meal or administered simultaneously with meals to be effective. This presents problems in cats who eat small amounts of food all day and this may make aluminum hydroxide ineffective in these patients.

West Nile Virus

The West Nile virus that was detected on the East Coast last summer has made a come back this summer. This virus is most likely to infect and kill birds, especially crows, but there have been reported deaths in humans, horses and one kitten (DVM Newsmagazine August 2000). The kitten is the only known feline victim and was found in New Jersey. Adult cats and dogs are considered to be unlikely to have clinical illness from this virus, though and should not be involved with transmission of the disease to humans.

Eastern Equine Encephalomyelitis (EEE)

This is another disease that has been affecting the East Coast this year. This is primarily a virus of birds and horses, as well. Humans can develop this infection and there have been some deaths in humans, this year. Due to this, I have been asked a number of times whether this virus can infect dogs and cats and if so, if they can transmit it to a human. There are a few scattered reports of infection in dogs but in general there seems to be good resistance to this virus in dogs. I haven't found reports of death or infection from the virus in cats. Both species are thought to be incapable of serving as reservoirs for this virus. This virus is spread by biting insects from birds to susceptible species, including humans, so avoiding walking dogs during the peak mosquito times might be a good precaution for dogs and their owners.

Losing Toe Nails

For some time it has been apparent that rottweilers are prone to a disorder in which they lose toe nails, usually one at a time, over the course of several months, until all nails are affected. When nails grow back after being lost they tend to be soft (crumbly), short or misshapen. This condition has been a mystery. It is now recognized to occur in other dog breeds, including German shepherds and schnauzers. There is still no known cause but the disorder has its own name now. It is being called lupoid onchodystrophy. My own rottweiler developed this problem and did not respond well to medical therapy, which seems to be a common occurrence.

The condition is usually treated with high (immunosuppressive) dosages of prednisone or with tetracycline and niacinamide combination therapy. Fatty acid supplementation may be helpful. Although our rottie never regrew normal nails she was not uncomfortable walking after the nails were all affected and regrew, even though they were always short and easily broken at the tips.

Spironolactone Makes a Comeback

Prior to the availability of furosemide (Lasix Rx), many veterinarians used spironlactone as a diuretic for patients with congestive heart failure. Furosemide is a more effective diuretic so it rapidly replaced spironolactone. However, spironolactone is better at suppressing aldosterone. This is now thought to be a very beneficial effect, as aldosterone suppression lowers sodium retention and also contributes to fibrosis of heart muscles and blood vessels.

At first, it seemed like a good idea to go back to spironolactone as the first choice diuretic for heart failure in dogs but it has been determined that the aldosterone suppression occurs at dosages of 0.25 to 1mg/kg per day, which is below the diuretic dose. This allows the use of spironolactone for its strong effect, aldosterone suppression, and to use furosemide at normal doses for its better diuretic effect. Other cardiac medications, such as enalapril and digoxin can be used in addition to spironolactone and furosemide so there is usually no need to change present therapies when adding spironolactone.

Vaccine Associated Sarcomas

For several years it has been apparent that some vaccinations administered to cats had the potential to induce cancers (sarcomas) at the injection site. These tumors are highly invasive and are malignant. Fibrosarcomas form naturally in cats, as well, so not all of these tumors are due to vaccination. It does not matter, from a treatment standpoint, whether the tumor is associated with vaccination or not. It is imperative that the tumor be identified properly, preferably prior to the first surgical attempt to remove it. Based on experience with these tumors to date, carefully planned and very aggressive surgery designed to remove the tumor and at least 2cm of tissue around the tumor, in every direction, provides about a 50% chance for a surgical cure. If the first surgery is unsuccessful in removing all cancerous cells, the cure rate for second or even third surgical attempts is much lower, probably 20% or less. For this reason it is critical that the first surgery be done properly. If your cat is suspected to have a vaccine associated sarcoma it is best to have surgery performed by a surgical specialist or oncology specialist who is experienced a oncological surgery. Most veterinarians will not remove sufficient tissue under the tumor, or in some cases around the tumor, due to the need to remove healthy bone that is in the 2cm zone. I refer these cases due to the need to remove the spinal processes (the bones that form the ridge of the back) or portions of the shoulder blade, in a number of cats with this problem. I would prefer to send these patients to a facility that can do contrast enhanced MRI or CT studies in order to help plan the surgery. If your vet feels that he or she is the best person to remove one of these tumors ask specifically what they intend to do about removing bone around the tumor and how they are going to identify affected areas. This is one surgery where the first chance is usually the only chance to get it right.

Canine and Feline Mammary Gland Tumors

For some time, I have been relying on studies that reported canine mammary gland tumors as being malignant about 20% of the time. More recent studies suggest that this figure is higher, with about 50% of canine mammary gland tumors now thought to be malignant. This higher figure justifies earlier removal of small mammary lumps and makes it more important to consider submitting mammary gland tumors to the pathologist to assess the potential for malignancy.

The great majority of feline mammary tumors are malignant, at least 90%. Siamese cats are approximately twice as likely to develop mammary cancer than other breeds of cats. Since approximately 1 in 4000 cats develops mammary cancer, overall, this makes the rate in Siamese cats about 1 in 2000, which is still not extremely high. It is a good idea to take chest X-rays, at least three views, and to consider having these reviewed by a radiologist prior to making a decision about surgery, since spread of the tumors makes it clear that the cancer is malignant and has spread. If no tumors are visible in the chest, radical mastectomy is the treatment of choice, with removal of the most affected side of the mammary glands first, followed by removal of the other side about a month later. Even with radical surgery and follow-up chemotherapy, the majority of cats with mammary tumors die within 1 year.

Acute Asthma Attacks in Cats

Terbutaline (Brethine Rx) comes in an injectable form, which can be given subcutaneously (directly under the skin) to cats having severe asthmatic attacks. It will normally have a beneficial effect within 5 to 10 minutes. This helps in the veterinary hospital, of course, but this is also something to consider for at home use, to help prevent visits to the emergency veterinary hospital, according to Dr. Philip Padrid, writing in Kirk's Current Therapy XIII. If the medication is working the heart rate should increase to approximately 240 beats per minute and/or the respiratory rate should decrease by about 50%.

United States Pharmacopeia's Veterinary Practitioner's Reporting Program

When an adverse reaction to a medication occurs it is best to report it to the drug manufacturer and the FDA (medications) or USDA (vaccines). To make reporting easier, the United States Pharmacopeia has established a central reporting service. If a veterinary practitioner reports a drug reaction, the USP-VPRP reports to the drug manufacturer, the FDA or USDA and the American Veterinary Medical Association with one phone call to 800-487-7776. The web site for this organization is www.usp.org.

Revolutionary Melanoma Treatment

Vets at the Animal Medical Center, in Manhattan, in cooperation with the Memorial Sloan-Kettering Cancer Center have developed a DNA based vaccine which works against melanomas, a malignant cancer in dogs. This vaccine has to be administered through special air injection syringes and is only available at the Animal Medical Center at the present time. If this method of treatment works, it would obviously be a major advance in therapy for melanomas and perhaps later for many cancers. (from DVM, May 2000).

Seizure Control Medications for Pets

Seizure control in pets can sometimes be extremely frustrating but there are some new medications and some new uses for old medications that can sometimes help when seizures are not responding to standard treatments.

Phenobarbital is the current standard medication for treatment of general seizures in dogs and cats. It is generally effective when serum levels of the medication can be maintained between 20 and 40 ug/ml. Due to the need to keep serum levels in this range, the dose range for phenobarbital is pretty wide, from 2 to 8mg/kg in dogs and 2mg to 4mg/kg in cats. It can take a month, or more, for this medication to reach a steady state in the serum and exert seizure control on a constant basis, so some patience is necessary when assessing the action of phenobarbital. It is when this medication does not work, or when it causes liver problems, that most people start to look for alternatives. Phenobarbital is addictive and it must be withdrawn slowly when it is discontinued to prevent complications such as an increase in seizure activity.

Primidone (Neurosyn Rx) is an older seizure control medication that is still favored by some vets, primarily because it is not a controlled substance, making record keeping requirements less burdensome. It is also the only seizure control medication that is actually approved for use in dogs. However, primidone is more likely than phenobarbital to cause liver disease and its method of action appears to be through conversion in the body to phenobarbital, so it is hard to justify its use its use in dogs. Primidone should not be used in cats due to neurotoxicity in this species, according to the prescription label for Neurosyn, but at least one clinical trial found no problems in the cats studied. There are occasional reports of dogs who respond to primidone when phenobarbital was not successful, but these are infrequent enough that other medications should probably be considered before primidone.

Potassium bromide is often used in conjunction with phenobarbital to aid in the control of seizures that can not be controlled with phenobarbital alone or to enable use of a lower dosage of phenobarbital when it is causing serious side effects. More recently, there are veterinarians who are trying this medication as a primary, or sole, seizure control medication. Potassium bromide has been used in both dogs and cats, although there are no controlled studies of its use in cats, that I know of. The usual dose for this medication is 20 to 30mg/kg/day but its use should be monitored by measuring serum blood levels, as well. It may take up to six weeks for bromide to reach consistent serum levels capable of controlling seizures, so it is necessary to look for long term results rather than short term results when using potassium bromide for seizure control. This medication causes significant incoordination in some dogs and cats, which may last for several weeks after starting the medication. This effect does resolve with time but it can be disturbing if people are not warned that it may occur.

Phenytoin (Dilantin Rx), which is used in humans is not used much in pets. In dogs, it has to be administered too frequently (at least three times a day) to make it practical as a chronic use medication for most clients. In cats, it has a very long half life (about 40 hours) which makes the chance for toxicity high enough to make most veterinarians reluctant to use phenytoin.

Diazepam (Valium Rx) can be used to control seizures in dogs but it has a very short duration of action and dogs develop resistance to its anti-seizure effect, so it is used primarily in attempts to stop long seizures (> 5 minutes) or to help prevent cluster seizures in this species. In cats, diazepam has a longer duration of action and is sometimes used as the only seizure control medication, since it doesn't seem to lose its effectiveness in cats the way that it does in dogs. The usual dose for use in cats, for long term seizure control, is 0.25 to 0.5mg/kg every 8 to 12 hours. Diazepam causes liver toxicity in some cats, usually 5 to 10 days after starting the medication, so it is important to carefully observe cats on this medication to be sure they continue to eat and feel well and it is a good idea to consider lab tests after a few days on the medication to check on the liver. In dogs, diazepam is used to stop seizures when they last more than a few minutes or to try to fend off clusters of seizures in dogs known to have this problem.The intravenous form of this medication is used in these cases, but it is possible to administer it rectally, rather than intravenously and achieve the same effectiveness. This makes it possible for pet owners whose dogs have very severe seizures, or who have cluster seizures, to treat their pets at home, after instruction from their veterinarian on the exact procedure and dosage for rectal administration for their pet. Diazepam may be given rectally in cats, if necessary to stop uncontrolled seizure activity. Diazepam is very sensitive to light and it can not be stored in a plastic syringe for long periods, so it is necessary for veterinarians to dispense it in the original injection vial and for pet owners to be able to accurately measure the medication into a syringe for use. It is a controlled substance and your vet may ask you to keep a log of the use of the medication for legal purposes.

There are some newer relatives of diazepam that will sometimes work as a second medication to control difficult seizures in dogs or that work better to stop current seizure activity in a few patients. These are clorazepate ( Tranxene-SD Rx) and clonazepam (Klonopin Rx). Clorazepate is usually dosed at 1 to 2mg/kg every 12 hours and used as an adjunct treatment with phenobarbital for seizures that are difficult to control. It seems to be particularly helpful as an aid in controlling cluster seizure activity. Clonazepam may be used long term as an aid to seizure control at dosages of 0.5mg/kg or it may be used like diazepam to stop continuous seizures (status epilepticus) when necessary.

Some dogs and cats have partial seizures. These pets will usually respond to general seizure control medications but not always. Felbamate (Felbatol Rx) is used in some dogs to control partial seizures with good success, even though it has not proven to be highly effective for generalized seizures. It is usually given at dosages of 20mg/kg three times a day and then adjusted from there. I have not seen any mention of the use of this medication in cats. Another relatively new seizure control medication that has found its primary use in the control of partial seizures is gabapentin (Neurotonin Rx). It is dosed based on patient response to the medication, usually starting with doses as low as 100mg/kg three times a day and then working up to doses as high as 1200mg/kg three times a day. Both felbamate and gabapentin may be helpful for control of generalized seizures when combined with phenobarbital or potassium bromide.

The combination of phenobarbital and potassium bromide has allowed veterinarians to control most seizure activity in pets since it was recognized that these compounds could be used at the same time for seizure control. Despite this, there are times when it is not possible to use this combination or when undesirable effects of the medications necessitate looking for other methods of seizure control. We are fortunate to have a number of seizure control medications to choose from at this time. With persistence it is usually possible to find a mediation, or combination of medications, that will control seizures.

There are still a few dogs and cats whose seizures prove to be difficult, or impossible, to control with medications. When it is necessary to use medications other than phenobarbital, potassium bromide and diazepam it may be beneficial to seek the help of a veterinary internal medicine specialist or veterinary neurologist, who will have more experience using the less commonly prescribed seizure control medications.

Out of Time

One of the comments (questions?) we get frequently from subscribers goes about like this: "my vet did not provide me with this much information, why not?"

I have thought hard about that question over the last couple of months, since I do practice veterinary medicine full time, as well as answering questions for the VetInfo web site. Our practice is small compared to most, due to its rural location on a peninsula surrounded by water, without much room for additional residents. This allows us to spend a little more time with our clients than many practices, but not a great deal more time. I wonder how many of my clients leave our practice feeling that they do not have adequate information to understand or perhaps even to treat their pet's problem.

A veterinary practice usually has seven or eight hours a day in which all of the pets who need to be seen that day must be scheduled to come in. This is usually done by scheduling appointments in ten minute, fifteen minute or perhaps half-hour intervals. Emergencies that occur are usually squeezed in between these appointments. Ideally, the receptionist can tell the difference between an appointment that will take ten minutes and one that will take an hour, but human nature being what it is, that doesn't always work well. So a practicing veterinarian usually sees 15 to 25 patients a day. A veterinary practice is a business and it must make a profit in order to keep opening its doors. It is a competitive business and it isn't usually possible for a vet to decide to see ten patients a day and just charge more, in order to have more time to diagnose and treat pets and discuss their problems with their owners.

The need to evaluate a pet's illness, make a treatment plan, explain that to the pet's owner and then get to the next patient doesn't leave a lot of time for detailed explanations of disease conditions, especially on a busy day. One of our worst nightmares is to have an emergency, a euthanasia with a distraught client and pet with a serious illness requiring a great deal of careful communication with an owner, such as diabetes or hyperadrenocorticism, all at the same time.

When you can tell that your vet is too fixated on getting through the day, rather than getting information through to you, or when there is obviously an emergency situation that is interfering with your pet's office visit, there are some things you should try to keep in mind.

If the situation with your pet is something like an ear infection, bladder infection or other disease in which a recheck visit will be beneficial, it may be best just to hold off on questions, see if the treatment works and then get additional information you need on the recheck visit, as long as you clearly understand the medication and treatment directions. Tell the receptionist you have a few questions you need to have answered since it was hectic during your first visit and he or she will probably schedule a little more time for the second visit.

If you are confused about an illness that requires immediate treatment, explain that. You may have to be a little patient and wait for someone who has time to get to your questions but if you are willing to do that most veterinary practices will find a way to make sure your questions are answered before you go. A veterinary technician may be able to help as much, or even more than your vet, if the question is routine, such as how to handle flea control, vaccination schedules or something of this nature. If your pet is a new diabetic, has immune mediated hemolytic anemia or some serious problem such as that, you need to stay until you understand the situation. This is also true of post-surgical care instructions for pets who have had orthopedic surgery or any procedure that might need more care than simply instructions to return in seven to ten days for suture removal. This is one time when passive aggression works well. Just stay at the veterinary hospital until someone fully explains the situation to you.

It bothers me that many clients leave our practice without a real understanding of their pet's problems. However, once in a while I spend as much as two to three hours researching a single question from a subscriber, in order to understand a problem enough to explain it. There are lots of problems that I can recognize, that I know the appropriate treatment for and that we manage routinely, that I do not understand well enough to answer detailed questions about. It would be very difficult for me and the client if I said something like "take a seat here in the exam room and I'll be back in a couple of hours to talk with you."

I think that there will always be a need for motivated clients to seek information on their own due to the restraints of business and the restraints of the human memory. No veterinarian can know enough detail about all subjects to satisfy the needs of all of their clients for information. I am glad that I have the opportunity to provide details to motivated pet owners that can not be conveyed in a standard office visit and have come to accept that my patients benefit from the effort but that my clients are sometimes just as shortchanged on explanation as the clients of any other veterinary hospital are.

Michal and I thank you for your support. Since the interest in the web site and newsletter has grown, it is harder for us to respond to questions quickly. We can't fully fix that problem and we do not wish to charge people for services they are not happy with. So, if we do not fully meet your expectations, we will refund the price of the subscription upon request.

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

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