Determination of tiamulin concentration in minipig plasma by LC-MS/MS and its application in pharmacokinetic studies of different formulations

The present study aimed to establish an LC-MS/MS method for the quantification of tiamulin in minipig plasma and to further conduct a pharmacokinetic comparison of different formulations. The plasma samples were extracted with acetonitrile (meloxicam as internal standard), separated on a C₁₈ column, and quantified by multiple reaction monitoring mode (ESI⁺). Sanyuan minipigs were used as experimental animals. Plasma samples were collected after intravenous injection (10 mg/kg) and intragastric administration (20 mg/kg). The method showed good linearity, with intra- and inter-batch RSD of 1.00%–8.13% and RE within ±15%. The extraction recovery, matrix effect and stability of the analytical methods met the relevant requirements. Tiamulin fumarate active pharmaceutical ingredient was intravenously administered, with c₀ of about (4383.73±2676.78) ng/mL, AUC_0-t of about (4803.50±965.68) h·ng/mL, t_1/2 of about (4.66±1.68) h, and CL of about (2.14±0.46) L/(kg·h). Three tiamulin formulations were intragastrically administered, with c_max of (552.00±328.55), (545.00±136.97) and (590.60±237.02) ng/mL, t_max of (1.47±0.68), (0.69±0.75) and (0.72±0.72) h, and F of 24.85%, 15.28% and 16.97%, respectively. The validated method meets the requirements for biological sample analysis and is applicable for the pharmacokinetic evaluation of tiamulin formulations in minipigs.