Giardia spp. infection is common in healthy dogs. The objective of this study was to determine whether administration of drugs with known anti-Giardia activity would eliminate infection in healthy dogs.
Feces from healthy dogs evaluated in clinics in north central Colorado were assayed for Giardia spp. antigen using a commercially available kit (SNAP® Giardia, IDEXX Laboratories, Portland, Maine) and by fecal flotation using zinc sulfate centrifugation. Giardia spp. infected dogs were administered fenbendazole at 50 mg/kg, PO, daily for five days or nitazoxanide at 25 mg/kg, PO, twice daily for five days. The Giardia antigen assay and fecal flotation were repeated on samples collected on days 10, 14, and 34.
Overall, 16 Giardia spp. infected dogs were administered fenbendazole (seven dogs) or nitazoxanide (nine dogs). Excess salivation, vomiting, or diarrhea developed in three fenbendazole-treated dogs and five nitazoxanide-treated dogs resulting in removal from the study. Of the dogs that completed the treatment protocols, six of eight (two fenbendazole; four nitazoxanide) were positive in one or both tests on Day 10, four of eight (one fenbendazole; three nitazoxanide) were positive in one or both tests on Day 14, and five of eight (two fenbendazole; three nitazoxanide) were positive in one or both tests on day 34.
As both drugs have been used safely in other studies, the cause of the potential side-effects is unclear. Of treated dogs, 62.5% were Giardia positive on day 34 suggesting persistent infection or re-infection.