Determination of equilibrium solubility and apparent oil-water partition coefficient of tulathromycin
Zhong Yawen
Li Ziyang
Wei Zhifei
Chen Jiaqi
Wu Chunxuan
Xiang Yifei
He Jiakang
Abstract：This study aimed to determine the equilibrium solubility of tulathromycin in phosphate buffers at different pH values and its apparent oil-water partition coefficient(Pow)in n-octanol/water and buffer systems,providing references for developing new tulathromycin formulations.A high-performance liquid chromatography(HPLC)method was established and validated for tulathromycin quantification through precision,stability,repeatability,and recovery tests.The equilibrium solubility of tulathromycin was measured in phosphate buffers(pH 1.0～8.0)and ultrapure water,while the apparent Pow was determined using the shake-flask method in n-octanol/buffer systems across varying pH levels.Results demonstrated that tulathromycin was very slightly soluble in pH 1.0 phosphate buffer,practically insoluble at pH 4.5,5.8,and 6.8 buffers,and insoluble at pH 7.4,8.0 buffers and ultrapure water.The logarithm of Pow(lgPow)ranged between 0 and 1.The established HPLC method exhibited excellent specificity for tulathromycin quantification.Tulathromycin demonstrated poor water solubility with moderate lipophilicity,and both its equilibrium solubility and Pow were pH-dependent,suggesting favorable biomembrane permeability.
Keywords：TulathromycinHigh-performance liquid chromatography(HPLC)Equilibrium solubilityApparent oil-water partition coefficient
Publication Date：2025-07-15
Online Publishing Date：2025-08-22(First online date of this platform, not the publication date of the document)
Pages：5( 1-5 )