Page 228 - Small Animal Internal Medicine, 6th Edition

200 PART I Cardiovascular System Disorders

Coughing or (less often) dyspnea after treatment can be as levamisole or stibophen as adulticides is not recom-
related to the HWD itself (pneumonitis), inflammatory reac- mended. Levamisole does not consistently kill adult HWs,
VetBooks.ir tion in the lungs and pulmonary vasculature secondary to although it is somewhat effective against male worms and
may sterilize adult female worms.
worm die-off, or dead worm fragments causing PTE. In
The use of a flexible alligator forceps with fluoroscopic or
general, these reactions are steroid responsive and can be
mitigated by administration of antiinflammatory prednisone transesophageal echocardiographic guidance has been advo-
course concurrently with melarsomine. Most clinical signs cated as a way to reduce the worm burden in accessible seg-
noted in dogs treated with melarsomine have been behav- ments of the main or branch pulmonary arteries before
ioral (e.g., tremors, lethargy, unsteadiness and ataxia, rest- adulticide therapy, even in dogs without caval syndrome.
lessness); respiratory (e.g., panting, shallow breathing, Removing as many worms as feasible reduces the risk for
labored respirations, crackles); or injection-site related (e.g., postadulticide PTE in heavily infected dogs. However, this
edema, redness, tenderness, vocalization, increased aspartate procedure is not routinely performed due to requirements
aminotransferase and creatine kinase activities). Injection for imaging equipment and technical expertise, the need for
site reactions are generally mild to moderate and resolve sedation or anesthesia, and the potential for worm breakage
within 4 (to 12) weeks. Occasionally these reactions are with exacerbated pulmonary reaction.
severe. The manufacturer reports that firm nodules might
persist indefinitely at the sites. General signs of lethargy, POSTADULTICIDE PULMONARY
depression, and anorexia occur in about 15% or fewer dogs; THROMBOEMBOLIC COMPLICATIONS
other adverse effects, including fever, vomiting, and diar- Pulmonary arterial disease worsens from 5 to 30 days after
rhea, occur occasionally. Adverse effects generally are mild adulticide therapy and can be especially severe in previously
at recommended doses. Hepatic and renal changes have not symptomatic dogs. Dead and dying worms promote throm-
proved clinically relevant in animals receiving recommended bosis and pulmonary artery obstruction, with exacerbation
doses of melarsomine. Overall, melarsomine causes less sys- of platelet adhesion, myointimal proliferation, villous hyper-
temic toxicity than its predecessor, thiacetarsamide. Never- trophy, granulomatous arteritis, perivascular edema, and
theless, melarsomine has a low margin of safety. Overdose hemorrhage. Severe ventilation-perfusion mismatch may
may cause collapse, severe salivation, vomiting, respiratory result from pulmonary hypoperfusion, hypoxic vasocon-
distress resulting from pulmonary inflammation and edema, striction and bronchoconstriction, pulmonary inflamma-
stupor, and death. tion, and fluid accumulation. PTE is most likely to occur 7
Strict exercise restriction should be enforced for 4 to 6 to 10 days after adulticide therapy but can occur up to 4
weeks after each dose of adulticide therapy to reduce the weeks later. As expected, the caudal and accessory lung lobes
effects of adult worm death and PTE. The rest period for are most commonly and severely affected. Pulmonary blood
working dogs should probably be longer because increased flow obstruction and increased vascular resistance further
pulmonary blood flow in response to exercise exacerbates strain the RV and increase oxygen demand. Poor cardiac
pulmonary capillary bed damage and subsequent fibrosis. output and hypotension can result.
HW Ag testing (with concurrent microfilaria testing) is Depression, fever, tachycardia, tachypnea or dyspnea, and
recommended 6 months after the final adulticide injection; cough are common clinical signs. Hemoptysis, right-sided
results should be negative with successful treatment. Many CHF, collapse, or death can also occur. Interstitial and alveo-
dogs are HW Ag-negative by 3 to 4 months after adulticide lar pulmonary inflammation and fluid accumulation cause
therapy. Persistent antigenemia 6 months after three-dose pulmonary crackles on auscultation. Focal lung consolida-
melarsomine protocol may occur due to latent worm die-off, tion can cause areas of muffled lung sounds. Thoracic radio-
persistence of a small number of live worms postadulticide, graphs show patchy alveolar infiltrates with air bronchograms,
or reinfection if monthly preventative was not given consis- especially near the caudal lobar arteries. Thrombocytopenia
tently. The Ag test should be repeated again 6 months later. or neutrophilia with a left shift may be seen on CBC.
A positive Ag test 12 months posttreatment despite adher- Treatment of PTE (whether it occurs before or after adul-
ence to a monthly preventative schedule suggests persistent ticide therapy) includes strict rest (i.e., cage confinement)
infection. Because the three-dose melarsomine protocol kills and glucocorticoid therapy to reduce pulmonary inflamma-
98% of worms, some dogs will remain Ag positive after treat- tion (e.g., prednisone, 0.5 mg/kg PO q12h for a week, then
ment due to presence of a small number of residual worms. decreasing to 0.5 mg/kg q24h for a week, then decreasing
The decision to repeat adulticide therapy is guided by the again to 0.5 mg/kg q48h for 1 to 2 additional weeks). Supple-
patient’s overall health, performance expectations, and age. mental oxygen therapy is recommended to reduce hypoxia-
Complete worm kill is probably not necessary; even if a few mediated pulmonary vasoconstriction, and sildenafil
adult HWs survive, pulmonary arterial disease improves (1-3 mg/kg PO q8-12h) is indicated to decrease pulmonary
considerably after adulticide therapy. vascular resistance. Antiplatelet therapy (clopidogrel or
Thiacetarsamide is an older arsenical agent that previ- aspirin), as well as anticoagulant therapy (unfractionated
ously was the only adulticide available. It had no advantages heparin or low-molecular-weight heparin), may be consid-
and greater toxicity potential compared with melarsomine ered for severe cases of thromboembolism. A bronchodilator
and is no longer used. Likewise, the use of other drugs such (e.g., oral theophylline, 10 mg/kg q12h); judicious fluid