Page 868 - Cote clinical veterinary advisor dogs and cats 4th

420 Heartworm Disease, Dog

• Antithrombotic therapy (aspirin or heparin) the venae cavae and right heart with alligator PROGNOSIS & OUTCOME
is not recommended. Caution should be used forceps, an endoscopic basket retrieval device, • Good in mild to moderate HWIs
VetBooks.ir Allergic pneumonitis: • Avoid damaging the heartworms when • Fair to guarded in severe cases
if corticosteroid and aspirin therapies are
or loop snare device
combined (not advised).
extracting them because PTE and/or
• Poor to grave even with treatment in caval
• Cage rest and corticosteroids (prednisone
anaphylactoid reaction may result.
1 mg/kg PO q 24h for 7-10 days) Microfilaricidal therapy: syndrome, severe PTE, and CHF
Adulticide therapy: • Current protocols using doxycycline with PEARLS & CONSIDERATIONS
• Melarsomine (immiticide) regular doses of macrocyclic lactones at
○ Up to 98% efficacy after three doses; 50% preventative doses have essentially eliminated Comments
of worm burden killed after a single dose the need for post-adulticidal elimination • Macrolide slow-kill adulticide method (using
○ Plan A: melarsomine administered once at of microfilariae. However, the clearance of preventive drugs rather than melarsomine)
2.5 mg/kg IM, followed by two injections microfilariae should be confirmed. does not prevent pathologic response and
at 2.5 mg/kg 24 hours apart, given 1-3 • Only imidacloprid-moxidectin (Advantage- potentially permanent or life-threatening
months later (authors’ preference if owner Multi) is approved by the U.S. Food and lesions from HWI. It also may contribute
finances allow) Drug Administration for the elimination of to the problem of resistance and is therefore
○ Plan B: melarsomine administered as two microfilariae. not recommended unless melarsomine is
2.5 mg/kg IM injections given 24 hours ○ Milbemycin and imidacloprid-moxidectin contraindicated.
apart are more rapidly microfilaricidal (adverse • Exercise restriction is an extremely important
Plan A is the option recommended reactions in approximately 10% of cases) part of HWI therapy.
■
by the American Heartworm Society at the preventive dosage. Patients should • Rarely, heartworm antigen testing may be
because Plan B results in reduced worm be hospitalized, pre-treated, and observed negative due to antigen-antibody complex
death (90% vs. 98%), and treatment for 8 hours for adverse reactions. formation. If HWD is suspected despite
success is generally less. ■ Shock, depression, hypothermia, and negative antigen and microfilaria tests,
○ Strict adherence to manufacturer’s vomiting commercial laboratories can heat treat serum
instructions for intramuscular injection ■ Fluid and corticosteroid (dexametha- for re-testing.
of arsenical agent sone 0.1-0.2 mg/kg IV) therapy, if • The American Heartworm Society
○ Consider corticosteroids (prednisone severe (www.heartwormsociety.org) is an excellent
1 mg/kg PO q 24h) or administration ■ Diphenhydramine 2 mg/kg IM and resource with up-to-date recommendations
of a nonsteroidal antiinflammatory drug dexamethasone 0.25 mg/kg IV may for diagnosis and treatment of HWD.
(NSAID) at manufacturer’s recommended be administered prophylactically to
dosage at the time of IM injections to prevent adverse reactions. Technician Tip
reduce injection-site inflammation. Technicians play a key role in educating clients
○ Doxycycline 10 mg/kg PO q 12h should Chronic Treatment about the importance of heartworm prevention.
be administered for 1 month before the • Preventive therapy
first treatment with melarsomine. ○ Prophylaxis should be administered in a Client Education
○ Exercise restriction for 4-6 weeks after melar- timely manner (i.e., every 30 days or 6 • HWI is a preventable disease.
somine injections is extremely important. months, depending on the product being • Yearly testing is advised.
• Macrolides as adulticides (i.e., slow kill) used). Reliance on the concept of the so- • For a client whose dog has just received
○ Ivermectin and selamectin at preventive called reachback effect is strongly discour- adulticide treatment, provide a client educa-
dosages have 40%-95% efficacy against aged. All are gradually microfilaricidal at tion sheet: How to Care for a Dog After
young HWIs when administered continu- preventive dosages except for milbemycin Heartworm Adulticide Treatment.
ously for 18 or 31 months, respectively. (rapidly microfilaricidal) and imidacloprid- • Small pockets of resistance have been
Moxidectin (Advantage Multi, Coraxis) moxidectin (approved as moderately rapid identified but are geographically restricted.
also has adulticidal effects. microfilaricide at preventive dosage). All preventives are highly effective in the
○ Milbemycin: modest adulticide activity ○ Ivermectin/pyrantel (Heartgard Plus: vast majority of instances.
○ Pulmonary and vascular manifestations ivermectin 6-12 mcg/kg, pyrantel 5 mg/ • Most preventives are broad-spectrum
of HWI still result during macrolide kg PO monthly), or antiparasitic drugs.
adulticide therapy, especially if patient is ○ Selamectin (Revolution): 6-12 mg/kg • Importance of year-round preventives
active. topically monthly, or ○ Adulticidal effect
○ Ivermectin or moxidectam at preven- ○ Milbemycin/spinosad (Trifexis: milbemy- ○ Other parasiticidal effects
tive dosage with a 4-week course of cin 0.5-0.999 mg/kg, spinosad 30 mg/kg ○ Reduced issues of compliance
doxycycline is reserved for cases in which PO monthly), or
financial constraints or concurrent medical ○ Moxidectin/imidacloprid topical (Advan- SUGGESTED READING
problems prohibit melarsomine therapy. If tage Multi; imidacloprid 10 mg/kg, mox- Atkins CE: Canine and feline heartworm disease. In
this therapeutic approach is taken, perform idectin 2.5-6.8 mg/kg topical monthly) Ettinger SJ, et al, editors: Textbook of veterinary
a microfilarae test in 4 months to ensure or moxidectin injectable (ProHeart 6 internal medicine, ed 8, Vol 1, St. Louis, 2017,
that microfilariae are cleared. 0.17 mg/kg SQ every 6 months) Elsevier, pp 1316-1343.
○ Use of the two-dose method (plan B), ■ Package insert states that injectable AUTHORS: Keith Nelson Strickland, DVM, DACVIM;
eschewing pretreatment workup if neces- moxidectin should not be administered Marisa Ames, DVM, DACVIM
sary, is a better option than macrolide to heartworm-positive dogs. EDITOR: Meg M. Sleeper, VMD, DACVIM
adulticidal therapy. In either instance, • CHF (p. 409)
doxycycline therapy for 30 days before • PH (arterial) (p. 838)
adulticidal therapy is recommended. ○ Adulticidal therapy when deemed safe
Worm embolectomy:
• Reserved for caval syndrome treatment Possible Complications
• Blind or fluoroscopically (or sonographically) • Injection-site inflammation (adulticide)
guided surgical removal of heartworms from • PTE

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