The pharmacokinetics of norethisterone in the rabbit and rat after systemic and oral administration: effect of phenobarbitone [proceedings].

ABSTRACT

PIP The pharmacokinetics of norethisterone in the rabbit and the rat after systemic and oral administration and the effect of phenobarbitone on pharmicokinetic parameters is presented. Norethisterone was given by iv and oral routes (85 mcg/kg) in the rabbit and by portal administration in the rat. Blood samples were collected over 24 hours in the rabbit and over 2 hours in the rat. Norethisterone was measured in plasma by radioimmunoassay. The plasma concentration-time curve was resolved into values for "fast disposition" half-life, "slow disposition" half-life, and the area under the curve (AUC). In the rabbit, AUC after oral administration was 53% of iv administration, while in the rat the AUC after portal administration was 32% of that after iv administration. In the rabbit phenobarbitone was without effect on plasma norethisterone concentrations after iv administration but significantly reduced the plasma concentration after oral administration. In the rat phenobarbitone had little effect on plasma norethisterone concentrations despite evidence of enzyme induction.^ieng