Bioavailability of dalarelin--a superactive GnRH analogue--in rats

125I-marked dalarelin (a modified analogue of GnRH) or GnRH (gonadotropin-releasing hormone) were administered to the tested rats in single doses of 127 ng/kg by subcutaneous injections. Dalarelin and GnRH were absorbed from the injected doses in 0.64 and 0.49%, respectively. Only one remarkable maximal concentration of these hormones was noticed in rats' blood 30 min after the administration. Dalarelin maximal concentration was 261.5 pg/cm3 and was 93.43% higher than the maximal concentration of GnRH. Dalarelin bioavailability was 1651.89 pg/cm3, whereas GnRH bioavailability was 718 pg/cm3 h. The bioavailability level of dalarelin was 230% compared with that for GnRH, which was accepted as a pattern of bioavailability.