Pharmacokinetics of Stable Caesium after Single Administration of Caesium Chloride in Japanese Black Cattle

Pharmacokinetic (PK) parameters of stable caesium (SCs) were determined in adult Japanese Black Cattle (JBC, n=20). They were divided into two groups, i.e, intravenous (IV) and oral (PO) administration groups, and each of them was administered 133 CsCl solution (20 mg/kg b.w.). SCs in biological samples was measured by ICP-MS, and their concentration-time courses were monitored for 182 days. The PK parameters determined in plasma and blood in each group were as follows (mean±SD); area under the concentration-time curve (AUC;µg/L · h): 0.54±0.06 (IVp), 0.42±0.05 (POp), 0.87±0.11 (IVb), and 0.71±0.33 (POb), mean residence time (MRT; day); 20.9±3.2 (IVp), 19.3±2.9 (POp), 24.7±3.6 (IVb), and 23.6±5.2 (POb), bioavailability (F%); 82±29 and 83±38, clearance (CL; mL/min/kg): 0.46±0.05 (IVp), 0.49±0.06 (POp), 0.29±0.04 (IVb), and 0.31±0.08 (POb), and distribution volume (Vd; L/kg) was 3.3 (Vdp) and 4.4 (Vdb). The biological half-life of the terminal elimination phase (T1/2) was estimated to be approximately 30 days. The urine recovery for the dose was 28±6 (IV) and 28±8 (PO), and the fecal recovery was 85±21 (IV) and 122±42% (PO). The time course via both routes of administration showed similar biphasic distribution and elimination profile in any biological samples and elucidated by compartment analysis with consideration of background level. Based on the PK parameters, elimination profile of radioactive caesium (RCs) from the JBC kept long in the RCs contaminated area can be explained.