HPLC-Method for Deliberation of Drug Mammary Transfer —Evaluation of Over-the-Counter Drugs (Loxonin®-S, Bufferin® A) in Mother Mice

Loxoprofen (Loxonin®), an antipyretic painkiller, was approved as an over-the-counter (OTC) drug (Loxonin®-S) in January 2011. With regard to self-medication using OTC drugs, the information that pharmacists provide to consumers is very important. Although loxoprofen is a very versatile drug and can be used during breastfeeding, information regarding its mammary gland transfer is inadequate. In this study, we established a simple method to evaluate mammary transfer of drugs, and compared loxoprofen's mammary gland transfer with that of aspirin. Loxoprofen 12 mg/kg and aspirin 132 mg/kg was orally administered to mother mice (ddY), and blood and milk samples were collected. Twenty microliters of ethanol was added to the blood and milk samples (10 μL), and the mixture was centrifuged for 15 min (12000 g); the supernatant was analyzed by high-performance liquid chromatography. Since aspirin was immediately metabolized, we analyzed salicylic acid concentrations. Maximum concentration of loxoprofen was observed at around 15 min after its oral administration, with the concentrations in the blood and milk being 2.9 and 0.5 μg/mL, respectively. The drug was metabolized promptly thereafter. In contrast, maximum concentration of salicylic acid was observed at 30 min after aspirin administration, with the concentrations in the blood and milk being 187.2 and 64.4 μg/mL, respectively. These concentrations remained constant from 60 to 120 min. Salicylic acid could be detected 240 min after aspirin administration. Thus, mammary gland transfer of loxoprofen is lower than that of aspirin, suggesting that loxoprofen does not accumulate in milk.