First published in Basenji Companions' newsletter March-April 1999
Giardia is a one-celled protozoan parasite that is a fairly common cause of diarrhea in dogs. By mechanisms that aren't well understood, the organisms interfere with absorption of nutrients in the small intestine, usually resulting in a characteristic, smelly, "cow-pat"-like stool. A number of drugs are available to treat this condition, among which are metronidazole (trade name: Flagyl), an antibiotic; albendazole (trade name: Valbazen), a wormer primarily used in cattle, sheep, goats, and swine; and fenbendazole (trade name: Panacur), used commonly as a wormer in dogs.
Of these drugs, metronidazole (Flagyl) is probably the most commonly prescribed. However, according to information provided by parasitologists at the Washington State University College of Veterinary Medicine and various published sources, between one-third and one-half of Giardia strains may be resistant to metronidazole. In addition, metronidazole is a drug with some significant toxicity issues. It has been implicated as a teratogen (cause of birth defects), and possible carcinogen, and can be associated with significant (reversible) neurotoxicity. Because of such issues, this is one of a relatively small group of drugs that is completely banned for use in any animal intended for food, for fear that any residues might enter the human food supply. While I'm sure note of us are planning to turn our Basenjis into burgers (!), such restrictions do bring home the seriousness of the matter.
Albendazole (Valbazen) is a drug that has been shown to have very high efficacy against Giardia, and in general has a very high margin of safety. However, there have been recent reports about severe bone marrow suppression (yielding serious anemia, very low levels of white blood cells and dangerously low levels of platelets) in small animals treated for Giardia with albendazole. Such reactions would appear to be very rare, but are something of which to be aware.
Fenbendazole (Panacur), seems to me to be the drug of choice for treatment of Giardia. It has been demonstrated to have excellent efficacy against the parasite, and is extraordinarily safe. It does not produce toxicity even at doses 100 times the recommended dose, and has been reported to be safe even for extended daily treatment in pregnant bitches and neonatal puppies.
In conclusion, I want to be careful to emphasize that there are definitely legitimate uses for metronidazole. It has, for instance, superb action against certain types of bacterial infections and several protozoal organisms and in such cases may be absolutely the drug of choice. In such circumstances, one should not hesitate to use it. However, in this case, there is a more reliable and much safer alternative. Fenbendazole is what I would use on my own dogs and what I will prescribe to my clients once I'm finished with my training and out in the real world again!
Bibliography
- Barr SC and DD Bowman. Giardiasis in dogs and cats. Compend Contin Educ Prac Vet 16(5):603-614
- Stokol T, et al. Development of bone marrow toxicosis after albendazole administration in a dog and a cat. JAVMA. 1997, June 15; 210(12):1753-6.
- Plumb, DC. Veterinary Drug Handbook (3rd ed.). Iowa State University Press. Ames, IA 1999.
- Tilley, LP and FWK Smnith. The 5 Minute Veterinary Consult. Williams & Wilkins. Baltimore. 1997.
Article copyright © 2001 by Jennifer Yearley.
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