Excretion of cefprozil into human breast milk

The excretion of cefprozil into breast milk in nine healthy, lactating female subjects was investigated. Each subject received a single 1,000-mg oral dose of cefprozil consisting of cis and trans isomers in an approximately 90:10 ratio. Serial blood, urine, and breast milk samples were collected and analyzed for the concentrations of the cis and trans isomers by a specific high-pressure liquid chromatography-UV assay. The mean pharmacokinetic parameters for both isomers were essentially the same. The mean peak concentrations in plasma for the cis isomer were 14.8 micrograms/ml, and the area under the concentration curve was 54.8 micrograms.h/ml. The mean values of elimination half-life, renal clearance, and urinary excretion for the cis isomer were 1.69 h, 164 ml/min, and 60%, respectively. The mean concentrations in milk of the cis isomer over a 24-h period ranged from 0.25 to 3.36 micrograms/ml, with the maximum concentration appearing at 6 h after dosing. The average maximum concentration in milk of the trans isomer was less than 0.26 micrograms/ml. The concentrations of the trans isomer in plasma and in breast milk were about 1/10 of those for the cis isomer. Less than 0.3% of the dose was excreted in breast milk for both isomers of cefprozil. Even if one assumes that the concentration of cefprozil in milk remains constant at 3.36 micrograms/ml (the highest concentration of cefprozil observed in breast milk), an infant ingesting an average of 800 ml of milk per day will be exposed to a maximum amount of about 3 mg of cefprozil per day. This value represents about 0.3% of the maternal dose. Low excretion of cefprozil in breast milk and the excellent safety profile of cefprozil suggest that this cephalosporin may be administered to nursing mothers when indicated.