The treatment plan should depend on the results of the FECRT. If FEC reduction is >95%, treatment should be considered effective. Drugs are not 100% effective, even against drug-susceptible worms; thus, some eggs may be seen, particularly when pretreatment FEC is high. Because resistance can be ruled out, eggs seen on previous fecal examinations are most likely a result of larval leakage. The patient should be treated with an anthelmintic monthly, and fecal examinations should be conducted every few months. Moxidectin can be a good choice in dogs with larval leakage, although any effective anthelmintic should work.
If FEC reduction is between 90% and 95%, FECRT should be repeated a few weeks later at the next treatment.
If FEC reduction is between 75% and 90%, FECRT can be repeated for more conclusive results, or because there is a high chance the worms are resistant, the treatment plan suggested below can be followed.
If FEC reduction is <75%, treatment should be considered ineffective and adjusted to a triple anthelmintic combination with all drugs administered concurrently at the labeled doses. Drugs should be administered sequentially on the same day and not mixed together.
This treatment plan has been successful in eliminating active infections in persistent hookworm cases26:
- Febantel (25 mg/kg PO)/pyrantel pamoate (5 mg/kg PO)/praziquantel (5 mg/kg PO) + moxidectin (2.5 mg/kg topical), or
- Fenbendazole (50 mg/kg PO once daily for 3 days) + pyrantel pamoate (5 mg/kg PO) + moxidectin (2.5 mg/kg topical)
Treatment success using this triple-drug combination depends on whether the hookworms are moxidectin-resistant. MDR hookworms studied by the authors were all ivermectin-resistant but may still be moxidectin-sensitive. The aforementioned regimen should be effective if hookworms are moxidectin-sensitive; however, this approach may be ineffective if the infecting source hookworms were previously treated with moxidectin. The authors have diagnosed recent cases of moxidectin-resistant A caninum in greyhounds in which monthly moxidectin treatments offered little benefit. If this monthly treatment regimen is effective in eliminating egg shedding, the patient will need to remain on this treatment for several months, or possibly for life, as somatic tissue stores will continually leak and repopulate the intestine for an extended time.
Extra-label administration at higher-than-label doses might improve efficacy, but there are currently no data to support such a recommendation. In addition, some parasitologists recommend repeating moxidectin treatment every 2 weeks for the first 4 treatments, then treating monthly, as this allows the moxidectin to rapidly reach a steady-state tissue concentration due to the long half-life of moxidectin in dogs.27-29 This is reasonable and potentially beneficial, although no specific data presently exist. Other products containing moxidectin may also be effective, but there are no published data to support the effectiveness of those products against MDR A caninum isolates.