OBJECTIVE To establish a liquid chromatography-tandem mass spectrometry （LC-MS/MS） method for the simultaneous determination of bepotastine and hydroxychloroquine concentrations in human breast milk and apply it in clinical practice. METHODS The milk samples （50 μL） were precipitated with 200 μL methanol containing the internal standard （100 ng/mL chloroquine）， and the supernatant was taken for analysis after vortexing and centrifugation. The separation was performed on a Waters ACQUITY UPLC HSS T3 column with mobile phase consisted of 0.1% formic acid-10 mmol/L ammonium acetate solution （phase A） and methanol （phase B） at gradient elution of 0.35 mL/min. The injection volume was 2 μL， and the analysis time was 4 min. The detection of the analytes was performed by electrospray ionization in positive mode by multiple reaction monitoring with the transition of m/z 388.9→201.9 （bepotastine）， m/z 336.3→247.1 （hydroxychloroquine）， and m/z 320.2→247.2 （chloroquine）. The established LC-MS/MS method was researched in methodology and used to determine the drug concentrations in the breast milk of 1 case of lactating patient. RESULTS The linear range of bepotastine was 2-200 ng/mL（ r＝0.999）， and hydroxychloroquine was 50-1 000 ng/mL （r＝0.998）. The intra-assay and inter-assay precisions were both ≤15%， and the accuracy， extraction recovery， matrix effect， and stability all met the acceptance criteria for bioanalytical method validation. The concentration result of bepotastine and hydroxychloroquine in the breast milk of the lactating patient showed， after 2 h and 14 h， the concentrations of bepotastine in the breast milk of the patient were 34.95 ng/mL and 5.72 ng/mL； those of hydroxychloroquine were 211.92 ng/mL and 104.18 ng/mL， respectively. The relative infant doses were 1.83% and 0.56%， respectively. CONCLUSIONS The established method is simple， rapid， and sensitive. It is suitable for simultaneous determination of bepotastine and hydroxychloroquine concentrations in human milk and can provide reference for safe drug use during lactation.

OBJECTIVE To establish a liquid chromatography-tandem mass spectrometry （LC-MS/MS） method for the simultaneous determination of bepotastine and hydroxychloroquine concentrations in human breast milk and apply it in clinical practice. METHODS The milk samples （50 μL） were precipitated with 200 μL methanol containing the internal standard （100 ng/mL chloroquine）， and the supernatant was taken for analysis after vortexing and centrifugation. The separation was performed on a Waters ACQUITY UPLC HSS T3 column with mobile phase consisted of 0.1% formic acid-10 mmol/L ammonium acetate solution （phase A） and methanol （phase B） at gradient elution of 0.35 mL/min. The injection volume was 2 μL， and the analysis time was 4 min. The detection of the analytes was performed by electrospray ionization in positive mode by multiple reaction monitoring with the transition of m/z 388.9→201.9 （bepotastine）， m/z 336.3→247.1 （hydroxychloroquine）， and m/z 320.2→247.2 （chloroquine）. The established LC-MS/MS method was researched in methodology and used to determine the drug concentrations in the breast milk of 1 case of lactating patient. RESULTS The linear range of bepotastine was 2-200 ng/mL（ r＝0.999）， and hydroxychloroquine was 50-1 000 ng/mL （r＝0.998）. The intra-assay and inter-assay precisions were both ≤15%， and the accuracy， extraction recovery， matrix effect， and stability all met the acceptance criteria for bioanalytical method validation. The concentration result of bepotastine and hydroxychloroquine in the breast milk of the lactating patient showed， after 2 h and 14 h， the concentrations of bepotastine in the breast milk of the patient were 34.95 ng/mL and 5.72 ng/mL； those of hydroxychloroquine were 211.92 ng/mL and 104.18 ng/mL， respectively. The relative infant doses were 1.83% and 0.56%， respectively. CONCLUSIONS The established method is simple， rapid， and sensitive. It is suitable for simultaneous determination of bepotastine and hydroxychloroquine concentrations in human milk and can provide reference for safe drug use during lactation.