SUMMARY Serum and milk concentrations of caffeine were measured in 5 breast-feeding mothers after a standardised oral dose of caffeine. Peak concentrations of caffeine in serum and milk were attained 60 minutes later. Binding of caffeine by constituents of serum and breast milk was low (25 and 3 *2 % respectively). In breast milk, caffeine binding is associated with the cream layer, and correlates with the butter fat content. Caffeine does not diffuse freely into breast milk and concentrations in milk are lower than in maternal serum.Most breast-feeding mothers will ingest daily some quantity of caffeine from coffee, tea, or soft drinks. Information about the passage of caffeine from serum into breast milk, however, is limited (Illingworth, 1953). We studied the relationship between serum and milk concentrations of caffeine after the ingestion ofa standardised oral dose.
SubjectsFive healthy white women participated in the study. The subjects ranged in ages from 25 to 31 years, weighed 53 1 to 70 kg, and had been nursing their infants for periods of 4 months to one year. The purpose and procedure of the study was explained to each woman and her informed consent obtained. Each was asked to refrain from taking any coffee, tea, or soft drinks in the 24-hour period immediately before the study.
MethodsAll studies were done approximately 2 hours after a morning meal. 150 or 300 mg caffeine in the form of caffeine sodium benzoate diluted with approximately 2 oz (60 ml) water was taken by each woman within a 3-min period. Blood and milk were collected at time 0 and at 30, 60, and 120 minutes after taking the caffleine.The caffeine concentrations in serum and breast milk were measured by gas liquid chromatography. 250 V.1 milk and 100 ,ud serum were pipetted into 12 ml conical tubes into which etidocaine, the internal standard, had previously been pipetted and dried. Samples were capped and stored at -200C until analysis. Extraction was carried out by adding 5 ml isopropyl alcohol and chloroform (5:95) to each specimen, mixing for 30 seconds with a Vortex mixer, freezing the aqueous layer by immersion of the tube in a dry ice and acetone bath, and decanting the organic layer. The extraction was repeated, and the organic phases pooled and dried under nitrogen.Each dried extract was redissolved in 50 V-1 chloroform and 2 Fd was injected into the gas chromatograph. A Hewlett-Packard 5830A gas chromatograph was equipped with a flame ionisation detector and a 1I8 m glass column packed with 3 %4 SE-30 on 100-120 Gas Chrom. Q (Applied Science). The initial oven temperature of 1950C was kept for 2 minutes and then it was increased at a rate of 20/min. Injector temperature was 2500C, and the detector temperature 3000C. Nitrogen flow was 35 ml/min. Retention time of caffeine and etidocaine were 3 * 44 and 6 * 8 minutes respectively. Peak height ratios were calculated and compared with drug supplemented standards processed identically for determination of concentrations of caffeine in the samples of milk and serum.