Organic arsenical compounds are the only effective heartworm adulticides.

Immiticide (Melarsomine dihydrochloride) [Rhone-Merieux]

Dosage:

Mild-moderate disease
2.5 mg/kg I.M., twice, 24 hours apart.

Severe disease
One injection 2.5 mg/kg then give complete treatment in one month. 2.5 mg/kg I.M., twice, 24 hours apart.

Contraindications
Caval syndrome.

Possible Reactions
Coughing, lethargy, decreased appetite, pulmonary thromboembolism.

Injections must be given deep in the epaxial muscularture to decrease the possibility of discomfort and abscessation.

Caparsolate (Thiacetarsamide) [Rhone-Merieux]

Dosage:

Contraindications
Neoplasia, renal failure, cardiomyopathy.

Possible Reactions
Hepatotoxicity, azotemia, vomiting, lethargy, anorexia.

Heartworm macrolides—given monthly, Heartgard or Heartgard Plus® (ivermectin) [Merck] or Interceptor® (milbemycin oxime) [Ciba Geigy]

Diethylcarbamazine—given daily, Filaribits or Filaribits Plus [Pfizer], and several other manufacturers.

The American Heartworm Society recommends that dogs be examined yearly for heartworm, even if they are on prophylaxis, because false negative status could occur if: initial testing was during the 6-7 month latent period after exposure; there was client non- compliance with giving preventive; and from possible problems with absorption of product (vomiting, spitting out, etc.) Testing should begin at 6 months of age.

Other recent articles include:

• American Heartworm Society Eighth Triennial Meeting. Canine Practice 20 (3): 15-18, 1995.
  
• LeSage, G. Freeman, KP: Critical use of heartworm antigen titers. Canine Practice 20 (3): 6-9, 1995.
  
• Hoover, JP, et al: Comparison of eight diagnostic blood tests for heartworm infection in dogs. Canine Practice 21 (1): 11-19, 1996.
  
• Hoover, JP, et al: Comparison of visual interpretations and optical density measurements of two antigen tests for heartworm infections in dogs. Canine Practice 21 (3): 12-20, 1996.