Safe and effective control of Mycoplasma gallisepticum: pharmacokinetic and residue profiling of doxycycline combined with quercetin nanomicelles.

Although doxycycline is widely used to combat Mycoplasma gallisepticum (MG), misuse promotes antimicrobial resistance. Quercetin exhibits antibacterial potential; however, its application is limited by poor bioavailability, and its nanomicelle-based delivery with doxycycline remains uninvestigated. This study evaluated the efficacy, pharmacokinetics, and residue depletion of doxycycline combined with quercetin and quercetin nanomicelles against MG infection in broilers using a validated green high-performance liquid chromatography approach. One-day-old chicks were divided into seven groups: negative and positive controls, and treatment groups that received doxycycline, quercetin, or quercetin nanomicelles orally at doses of 25, 50, and 50 mg/kg body weight, respectively, either alone or in combination, for five days post-challenge. Pharmacokinetic parameters and residue depletion were investigated in treated groups at multiple time points. Tracheal and lung samples were collected at two intervals for MG enumeration and virulence gene expression. Quercetin and its nanomicelles displayed minimum inhibitory concentrations (MICs) of 0.47 and 0.02 µg/mL, respectively; their combinations with doxycycline had fractional inhibitory concentration indices of 6 and 0.375, respectively. Nanomicelles were characterized by size, polydispersity index, zeta potential, and encapsulation efficiency values of 345.66 nm, 0.14, 19.1 mV, and 96.1%, respectively, with no cytotoxicity up to 8× MIC. In vivo, the greatest reductions in MG counts and in mgc2, adrA, and crmA expression were observed in nanomicelle-treated groups. Co-administration of doxycycline with nanomicellar quercetin improved systemic exposure, prolonged serum persistence above the MIC, and supported extended dosing intervals while maintaining favorable tissue depletion profiles. Conversely, conventional quercetin negatively influenced doxycycline pharmacokinetics, causing therapeutic failure.