Need Answers/opinions Regarding Heartworm/treatment

[Guest TanyaM]

A friend has an outside dog who has recently tested positive for heartworm (they have well-cared for outside dogs - they just live with a lot of natural area in their backyard). I have always heard that you do not start a dog on heartworm medication if they have already been diagnosed as having heartworms. They need to do the treatment (which is very expensive) and then when the dog is clear, they can use the treatment as a preventative.

 

The friend cannot really afford the heartworm treatment right now, but DBF and I spoke with an evet who indicated that it is okay to start the heartworm preventative medication, and that new ones will not start, and there is a possibility that the existing heartworms will die off. She said it's not a popular stance, and not one that you readily hear coming from vets, but if the issue is using the preventative vs. no treatment at this time, then use the preventative. The dog is a young male - about 4 years old.

 

As always, this board has lots of experienced individuals, so I am asking if anyone has heard of that approach, or what their opinions are on this. Is it dangerous? No judgement on the individual who cannot swing the heartworm treatment right now - they are willing to try the preventative and see how things go in the future i.e. resolve itself. (this particular dog made his way to their home due to another family no longer wanting him and he was going to be put down).

 

As mentioned above, this advice came straight from the e-vet.

 

Thanks for any opinions.

 

 

[Guest argolola]

We consulted with 2 vets that suggested the "unpopular" method, which is what we opted for.

 

Lola was heartworm positive when we adopted her and there were not funds at the adoption clinic for the expensive treatment. The track vet, as well as our personal vet, talked to us about HeartGard Plus. Within 6 months of only HeartGard Plus as treatment (and a lot of prayer) Lola was heartworm free. That was 3 1/2 years ago.

 

Please keep us posted.

Edited May 26, 2007 by argolola

[ahicks51]

A friend has an outside dog who has recently tested positive for heartworm (they have well-cared for outside dogs - they just live with a lot of natural area in their backyard). I have always heard that you do not start a dog on heartworm medication if they have already been diagnosed as having heartworms. They need to do the treatment (which is very expensive) and then when the dog is clear, they can use the treatment as a preventative.

 

The friend cannot really afford the heartworm treatment right now, but DBF and I spoke with an evet who indicated that it is okay to start the heartworm preventative medication, and that new ones will not start, and there is a possibility that the existing heartworms will die off. She said it's not a popular stance, and not one that you readily hear coming from vets, but if the issue is using the preventative vs. no treatment at this time, then use the preventative. The dog is a young male - about 4 years old.

 

As always, this board has lots of experienced individuals, so I am asking if anyone has heard of that approach, or what their opinions are on this. Is it dangerous? No judgement on the individual who cannot swing the heartworm treatment right now - they are willing to try the preventative and see how things go in the future i.e. resolve itself. (this particular dog made his way to their home due to another family no longer wanting him and he was going to be put down).

 

As mentioned above, this advice came straight from the e-vet.

 

Thanks for any opinions.

 

 

Treatment for existing heartworm infections is extremely dangerous. Here's what the Merck Veterinary Manual has to say (emphasis mine):

 

"The only available heartworm adulticide is melarsomine dihydrochloride, which is effective against mature (adult) and immature heartworms of both genders. For Class I and II patients, melarsomine is given at 2.5 mg/kg, deep IM in the epaxial (lumbar) musculature in the L3-L5 region using a 22 g needle (1 in. long for dogs <10 kg or 1.5 in. for dogs >10 kg). Pressure is applied during delivery and for 1 min after the needle is withdrawn to prevent SC leakage. The procedure is repeated on the opposite side 24 hr later. Approximately one-third of dogs will exhibit local pain, swelling, soreness with movement, or sterile abscessation at the injection site. Local fibrosis is uncommon.

 

Dogs with high worm burdens are at risk of severe pulmonary thromboembolism from several days to 6 wk postadulticide. Dogs with Class III infection receive the alternate (split-dose) regimen of 1 injection, followed in 1 mo by 2 injections 24 hr apart. Administration of a single initial dose results in a graded (~50%) worm kill and reduced pulmonary complications. By initially killing few worms and completing the treatment in 2 stages, the cumulative impact of worm emboli on severely diseased pulmonary arteries and lungs can be reduced. This 3-injection protocol is becoming the treatment of choice of many veterinarians regardless of stage of disease, due to its increased safety and efficacy.

 

Other treatment protocols recommend the administration of prophylactic doses of ivermectin for 1-6 mo prior to administration of melarsomine, if the clinical presentation does not demand immediate intervention. The rationale for this approach is to greatly reduce or eliminate circulating microfilariae and migrating D immitis larvae, stunt immature HW, and reduce female worm mass by destroying the reproductive system. This results in reduced antigenic mass, which in turns reduces the risk of pulmonary thromboembolism.

 

Following melarsomine injection, exercise must be severely restricted for 4-6 wk to minimize thromboembolic lung complications. A low cardiac output should be maintained in order to reduce thrombosis and endothelial damage and facilitate lung repair. Adverse effects of melarsomine are otherwise limited to local inflammation, brief low-grade fever, and salivation. Hepatic and renal toxicity are seldom seen.

 

Class III patients should be stabilized prior to melarsomine administration. Stabilizing treatment variably includes cage confinement, oxygen, corticosteroids, and heparin (75-100 U/kg, SC, tid) for 1 wk prior to the alternate melarsomine treatment protocol.

Patients with right-sided CHF should be treated with furosemide (1-2 mg/kg, bid), a low-dose angiotensin-converting enzyme (ACE) inhibitor such as enalapril (0.25 mg/kg, bid, possibly increased to 0.5 mg/kg, bid after 1 wk pending renal function test results), and a restricted sodium diet. Digoxin, digitoxin, and arteriolar dilators, such as hydralazine and amlodipine, should not be administered. Digoxin is not effective for cor pulmonale; arteriolar dilators, and occasionally even ACE inhibitors, are likely to cause systemic hypotension.

 

Postadulticide thromboembolic complications can occur 2-30 days following treatment, with signs most likely 14-21 days after treatment. Clinical signs are coughing, hemoptysis, dyspnea, tachypnea, lethargy, anorexia, and fever. Laboratory findings may include an inflammatory leukogram, thrombocytopenia, and prolonged activated clotting time or prothrombin time. A postinjection increase in serum CK may be noted. Local or disseminated intravascular coagulopathy may occur when platelet counts are <100,000/µL. Treatment for severe thromboembolism should include oxygen, cage confinement, a corticosteroid at an anti-inflammatory dosage (eg, prednisone at 1.0 mg/kg, PO, sid), and low-dose heparin (75-100 U/kg, SC, tid) for several days to 1 wk. Most dogs respond within 24 hr. Severe lung injury is likely if, after 24 hr of oxygen therapy, no improvement is noted and partial pressures of oxygen remain <70 mm Hg.

 

Both the standard melarsomine protocol and the alternate regimen kill all or most worms in ~75% of dogs. Antigen testing is performed 6 mo after the first 2 doses of the standard protocol or 4-6 mo after the third dose of the alternate protocol. A positive test result should be followed by retreatment (2 injections, 24 hr apart) if the antigen test is strongly positive, if the patient is still symptomatic, and if the patient is an athlete or a working dog. Mild infection, a weakly positive antigen test, absence of clinical signs, advanced age, and a sedentary dog are factors that may negate the need for a repeat melarsomine treatment. Maintaining dogs on ivermectin/pyrantel pamoate to slowly kill residual worms over the following 20 mo is an alternative in nonperforming dogs with a post-melarsomine weakly positive antigen test result.

 

Ivermectin/pyrantel pamoate administered monthly for ~2 yr beginning at 5-7 mo post-L3 inoculation eradicates most adult worms. Further, during this time period, some older worms are also killed. However, the use of ivermectin/pyrantel pamoate is seldom a substitute for melarsomine treatment because the slow kill may allow pulmonary pathology to progress in the interim.

In caval syndrome cases (class IV), surgical removal of worms from the right atrium and orifice of the tricuspid valve is necessary to save the life of the dog. This may be accomplished by using local anesthesia and either a rigid or flexible alligator forceps, or an intravascular retrieval snare, introduced preferentially via the right external jugular vein. With fluoroscopic guidance, if available, the instrument should continue to be passed until worms can no longer be retrieved. Immediately following a successful operation, the clinical signs should lessen or disappear. Fluid therapy may be necessary in critically ill, hypovolemic dogs to restore hemodynamic and renal function. Within a few weeks following recovery from surgery, adulticide chemotherapy is recommended to eliminate any remaining worms, particularly if many are still visible echocardiographically."

 

The 4-6 weeks of restricting activity is important as bits and peices of the worms break free; if they lodge in the lungs, cardiac arteries, or brain, that can be the end of Fluffy.

 

What the vet is recommending is presumably starting heartworm prophylaxis- presumably as ivermectin- to prevent, as you note, additional microfilariae from swimming around the system and taking up residence in the heart, as they do. If the titer is low, and the existing number of worms is small, this is presumably a "better-than-nothing" tack, and if you're *really* lucky, only one or two worms have taken up residence in the heart. The existing worms cannot reproduce effectively, and may even perish from the treatment (I *think*- I'm admittedly a little vague on that aspect of Dirofilariasis).

 

See also:

 

http://www.vetmed.auburn.edu/distance/cardio/aiello.htm

 

http://publications.royalcanin.com/renvoie...session=2138011

 

It is estimated that 50% of people who DO use heartworm preventatives don't use them correctly- hence the annual re-testing before handing out new meds. If one were to start prophylaxis on an animal that was already infected, it would be critical to stick with it for the remainder of the animal's life.

[Hubcitypam]

The long term Heartgard treatment is sometimes used on dogs that have compromised health and might not withstand the more expensive and harder on the system option. They have to do what they have to do -- and it can work.

[Burpdog]

I think I've heard of using Interceptor on heartworm positive dogs. With Heartguard (from memory because I don't use it) you cannot use it on some breeds like collies.

 

Can't they talk to a regular vet and see what he/she says? If they can get a vet on board with this type of treatment, it would be better all around.

[Guest KennelMom]

I think using the heartworm preventative method of treating heartworm infestations depends on what stage the infestation is at. With lower numbers of heartworms, you can just give the heartworm preventative, keeping them from getting any new heartworms and eventually the existing heartworms will die off leaving the dog clear of worms. If the dog has a high "worm count" I don't think it's recommended to treat that way. Not sure though...just recalling what I've read in the past in other threads.

 

Google American Heartworm Society...they have a lot of good information .

[Guest Tenderhearts]

When I worked for our small humane society here, I coordinated with both veterinarians. My vet refused anything other than the traditional treatment with the immiticide injections, but the other vet had successfully treated positive dogs giving the interceptor.

[Guest LynnM]

Yes, one can treat with Heartguard (the dosage in the chewables is low enough that it *is* safe for ivermectin sensitive herding breeds) over a long period of time, so that hopefully the adult worms die of old age and no new ones mature to take their place. When we've done it, we do it every 2 weeks (so you're only killing 2 weeks worth of larvae, rather than a whole month's worth). The rationale is that clearing a less more often is less stressful on the dog's system than clearing more, less frequently. Actually, any of the commercially available heartworm preventatives except, perhaps, Filaribits, will not harm a heartworm positive dog.

 

Remember that commercially available Heartguard WILL NOT clear microfilarae. Only a higher dose of ivermectin will do this, and if the vet decides they need to do that, it's best to premedicate with Benedryl (Pred, too, if he wants to be really careful). If bad things are going to happen, doing this is what's going to cause them, but it is sometimes necessary. Only the vet can determine that.

 

Lynn

Edited May 26, 2007 by LynnM

[Guest TanyaM]

Thanks so much for the replies. I will hunt around on the internet and see what else I can find out. Finances are an issue for them, but I'll see if they can get an opinion from a local vet (or tap that evet again and see what else she says). I saw that the heartguard plus is presciption formula - we'll have to find a vet that will go along with that approach and get a presciption for it.

 

I wonder if the local humane society or animal control offers any 'mobile vet' clinics, conceptually like a free clinic for people except for animals where folks can't really afford vet fees?

 

Thanks - as always, some great advice here.

[Guest MeAndMyDog]

As a former vet tech (in the deep south) and having recently adopted and treated a HW+ dog myself, here's what I've seen to be the case:

 

It is safe to give Heartgard to a HW+ dog and I think it's even FDA approved for use in HW+ dogs. This will kill the microfilaria (that's how it prevents new infections). Obviously, they won't stay gone because the adults will keep producing them. It also reduces the risk of transmission to other dogs in the area. I've never heard that it won't kill all of them, but if someone has better information than me, I'm not one to argue. It might not be a bad idea to give the first dose under veterinary supervision. I've seen this done at clinics I've worked at, but none of the dogs ever had a problem. Most vets that I worked for would prescribe Heartgard if the dog was unable to undergo the Immiticide treatment for any reason (finances, health problems, too hyper to keep crated for weeks at a time, etc.)

 

DO NOT give Interceptor. The Heartgard (ivermectin) kills slowly, which causes the microfilaria to die off slowly. The Interceptor (milbemycin oxime) kills very quickly which is not an issue if the dog doesn't have a high microfilaria burden. However, if the dog does have an advanced infection, large numbers of microfilaria dying quickly can send the dog into anaphylaxis. I actually treated a case like this while working in an emergency clinic in Atlanta.

 

 

[VinnieAndRexsMom]

I think I've heard of using Interceptor on heartworm positive dogs. With Heartguard (from memory because I don't use it) you cannot use it on some breeds like collies

As Lynn stated, there is a Heartguard for collies/herding dogs. We used it on Bobby since he appeared to be a terrier/border collie mix. Since we always went to the same vet, I didn't have to worry about which Heartguard we got because it was in his files, but for folks who buy online, they will have to be cautious. I'm only including my response because the original post doesn't say what breed the outside dogs are.

Edited May 27, 2007 by VinnieAndRexsMom