Effects of monensin on the bioavailability and elimination of selenium from blood in lambs.

A bioavailability study was conducted in lambs following intravenous and oral administration of sodium selenite (0.4 mg selenium/kg body weight) with and without concurrent oral monensin. Two- or three-compartment open models with first-order absorption after oral administration adequately described plasma selenium disposition irrespective of whether monensin was being administered. No significant differences were observed between groups of lambs receiving intravenous selenium with or without monensin with respect to distribution or elimination half-lives of selenium, areas under the concentration-time curve (AUC), volumes of distribution (Vd(ss)), or clearances (Cl). In lambs given selenium per os, no significant differences were observed with animals receiving monensin as well with respect to absorption and elimination half-lives, Vd(ss), or the time at which peak selenium concentrations occurred (tmax). However, peak selenium levels (Cmax) and AUC values were significantly higher in the group given monensin. The bioavailability of selenium with and without monensin was estimated to be 60% and 43%, respectively.