Relative bioavailability of rafoxanide following intraruminal and intra-abomasal administration in sheep

The bioavailability of rafoxanide was compared after intraruminal and intra -abomasal administration in healthy adult sheep (n = 6) in a single dose, 2 parallel group study at 7.5 mg/kg. Rafoxanide concentrations in plasma wer e measured by means of HPLC analysis. Primary pharmacokinetic parameters fo r bioavailability and disposition of rafoxanide in plasma for both routes o f administration were determined by noncompartmental and non-linear, I-comp artmental pharmacokinetic analysis, respectively. Significantly (P less tha n or equal to 0.05) higher peak plasma concentrations ((C)max) of rafoxanid e and a more rapid rate of absorption (c. 3.5 times) was observed in sheep after intra-abomasal (i-a) administration compared to intraruminal (i.r) ad ministration. A significantly(P less than or equal to 0.05) longer lag peri od (t(lag)) before absorption (6.8 +/- 2.9 h) occurred after i.r. than afte r i-a treatment (1.9 +/- 0.6 h). There was no significant difference (P > 0 .05) in AUG, MRT and in the rates of elimination (k(10)-HL and t1/2(ss)) be tween the i.r. and i-a routes of administration. The results of the study d emonstrated the important influence of the rumino-reticulum on absorption o f rafoxanide in sheep.