Quantitation of free drug by LC-MS/MS with ultrafiltration separation and application to toxicity and toxicokinetic study of liposomal drug

China Bioanalysis Forum 2025 -- Typical antibiotic treatments are often ineffective against biofilm-related infections since bacteria residing within biofilms have developed various mechanisms to resist antibiotics. To overcome these limitations, antimicrobial-loaded liposomal nanoparticles are a promising anti-biofilm strategy as they have demonstrated improved antibiotic delivery and eradication of bacteria residing in biofilms. Drug A is an oxazolidinone antibacterial drug, encapsulated into liposome for delivery to the site of infection. For pharmacokinetic investigation and safety evaluation of liposomal formulations, it is essential to assess the plasma profiles of both liposome-associated and free (or non-liposomal) drugs. Hence, sample preparation to separate the different forms while maintaining integrity of the liposome and avoiding contamination of nonencapsulated drug by liposome is a critical component of a successful bioanalytical method for a liposomal drug. A sensitive and specific LC-MS/MS method in nonhuman primate (NHP) plasma has been developed to effectively separate and quantify the free drug utilizing ultrafiltration. The method was used in the bioanalysis of free drug A of liposomal drug in NHP toxicity and toxicokinetic study, in which incurred samples have extremely low free drug (0.011%~0.12% free rate of liposome).