Heartworm drug resistance: It's real

[sinkingfeeling]

http://news.vin.com/VINNews.aspx?articleId=28284

In the world of canine heartworm disease research, reluctance to use the R word has evaporated. Leading authorities in pet parasites now concur that resistance to the class of drugs used in heartworm preventive drugs is real.

“We now have proof there is resistance to the macrocyclic lactone (ML) class,” said Dr. Byron Blagburn, an Auburn University parasitologist who did much of the research on strains of heartworm found in the Mississippi Delta, where loss of efficacy to preventive drugs was first suspected. “It’s accepted by the entire industry now,” Blagburn said.

The macrocyclic lactone class of drugs in question comprises avermectin drugs (ivermectin and selamectin) and milbemycins (milbemycin oxime and moxidectin). These drugs are found in all commercial heartworm preventives, including: Heartgard (ivermectin), Tri-Heart Plus (ivermectin), Sentinel (milbemycin oxime), Revolution (selamectin), Advantage Multi (moxidectin), ProHeart6 (moxidectin), and Trifexis (milbemycin oxime).

The resistance finding begs the question: Is there any point to using the products?

Absolutely, say Blagburn and Little. Both state that the preventive products still work very well. There may be breaks in prevention with certain products in certain areas, but to the expert mind, this state of affairs only increases the need for year-round preventive action and annual testing for heartworm disease.

“To make a presumption that because resistance exists, the products should be discontinued is absolutely ludicrous,” Blagburn said.