Isotope tracer labeling method for determination of sifuvirtide concentration

125I-sifuvirtide is over 99.0%, and the specific activity of ¹²⁵I-sifuvirtide is 3.9 GBq•g-1. The labeled product still maintain some biological activity. The radioactivity in plasma is determined by trichloroacetic acid precipitation method. The pharmacokinetics of 125I-sifuvirtide is successfully modeled using two-compartmental after subcutaneous (SC) or intravenous (IV) administration in rhesus monkeys according to the curve of radioactivity of TCA precipitable vs time. The mean half-life (t1/2) value is 95.83 h, the mean time to maximum concentration is 3.35 h, and the mean bioavailability is 85.2% after SC administration.125I-sifuvirtide is prepared by Iodogen method, the radiochemical purity of