The pharmacokinetics of (-)-N-(trans-4-isopropylcyclohexanecarbonyl)-D-phenylalanine (nateglinide) and its enantiomer (L-enantiomer) was studied in Goto-Kakizaki (GK) rats after intravenous administration of nateglinide or L-enantiomer at a dose of 40 micromol/kg body weight. Nateglinide, its L-enantiomer and their metabolites in serum, bile and urine were determined. The total clearance (CL(tot)) and the volume of distribution (Vd) was slightly higher for nateglinide than those for L-enantiomer in control rats, although the differences were not statistically significant. The cumulative excretions of L-M1 (major metabolite of L-enantiomer) and L-M2 (major metabolite of L-enantiomer) into bile were almost the same as that of M1 (major metabolite of nateglinide)and M2 (major metabolite of nateglinide). In GK rats, CL(tot) and Vd were higher for nateglinide than those for L-enantiomer. The cumulative excretion of L-M1 and L-M2 were not different from those of M1 and M2, respectively, into bile or urine. CL(tot) and Vd for nateglinide or L-enantiomer in GK rats were not different from those in control rats. The total excretion of M1, M2, L-M1, and L-M2 into bile or urine in GK rats was not substantially different from that of control rats. These results suggest that the L-enantiomer of nateglinide shows higher CL(tot) and Vd compared with nateglinide, especially in the diabetic state.
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