Ivermectin disposition kinetics after subcutaneous and intramuscular administration of an oil-based formulation to cattle

Slight differences in formulation may change the plasma kinetics and ecto-e ndoparasiticide activity of endectocide compounds. This work reports on the disposition kinetics and plasma availability of ivermectin (IVM) after sub cutaneous (SC) and intramuscular (IM) administration as an oil-based formul ation to cattle. Parasite-free Aberdeen Angus calves (n=24; 240-280kg) were divided into three groups (rt = 8) and treated (200 mu g/kg) with either a n IVM oil-based pharmaceutical preparation (IVM-TEST formulation) (Bayer Ar gentina S.A.) given by subcutaneous (Group A) and intramuscular (Group B) i njections or the NM-CONTROL (non-aqueous formulation) (Ivomec(R), MSD Agvet ) subcutaneously administered (Group C). Blood samples were taken over 35 d ays post-treatment and the recovered plasma was extracted and analyzed by H PLC using fluorescence detection. IVM was detected in plasma between 12h an d 35 days post-administration of IVM-TEST (SC and IM injections) and IVM-CO NTROL formulations. Prolonged IVM absorption half-life (p < 0.05) and delay ed peak plasma concentration (p < 0.001) were obtained following the SC adm inistration of the IVM-TEST compared to the IVM-CONTROL formulation. No dif ferences in total plasma availability were observed among treatments. Howev er, the plasma residence time and elimination half-life of IVM were signifi cantly longer after injection of the IVM-TEST formulation. IVM plasma conce ntrations were above 0.5 ng/ml for 20.6 (CONTROL) and 27.5 days (IVM-TEST S C), respectively (p < 0.05). The modified kinetic behaviour of IVM obtained after the administration of the novel oil-based formulation examined in th is trial, compared to the standard preparation, may positively impact on it s strategic use in cattle. (C) 1999 Elsevier Science B.V. All rights reserv ed.