Measurement of ivermectin concentrations in the host gastrointestinal tissues and in Haemonchus contortus recovered from infected lambs

LIFSCHITZ, A.; LLOBERAS, M.; ALVAREZ, L.; ENTROCASSO, C.; BALLENT, M.; VIRKEL, G.; BORDA, B.; LANUSSE, C.

Calgary, Canada

Conferencia; 22 International Conference of the World Association for the Advancement of Veterinary Parasitology; 2009

Asociacion Mundial para el avance de la Parasitología Veterinaria

An improved efficacy against gastrointestinal resistant nematodes in sheep and goats has been documented when the macrocyclic lactones are administered orally compared to their subcutaneous injection. This work aimed to assess the influence of the IVM administration route on the relationship among concentration profiles achieved in the bloodstream, the gastrointestinal fluid/tissues and in a target abomasal parasite (H. contortus) in lambs naturally infected. Twenty (20) parasitized lambs were assigned into two experimental groups treated with IVM either intraruminally or subcutaneously at 0.2 mg/kg. Blood samples were collected from six animals in each treated group between 0 and 15 days post-treatment (plasma disposition study). Four animals from each group were sacrificed at day 3 post-treatment. Mucosa and content samples from abomasum and small intestine were collected. Adult specimens of H. contortus were recovered from the abomasum. Drug concentrations were measured by HPLC. The IVM plasma availability was higher (P<0.05) after the subcutaneous administration. However, IVM concentrations recovered in the gastrointestinal contents were higher in lambs treated by the intraruminal route. The ratio between IVM concentrations measured in the abomasal contents and mucosa were 0.07 (subcutaneous) and 2.97 (intraruminal). The content/mucosa ratios in the small intestine were 1.39 (subcutaneous) and 1.99 (intraruminal). IVM concentrations were 15-fold higher in H. contortus recovered from intraruminally treated lambs. The higher IVM concentrations achieved in the digestive tract shortly after the oral treatment may account to the observed enhanced efficacy compared to the parenteral administration against parasites of reduced susceptibility.