Monitoring of phenytoin in human breast milk, maternal plasma and cord blood plasma by solid-phase extraction and liquid chromatography.

A rapid liquid chromatographic method for the quantitation of phenytoin in human breast milk, maternal plasma and cord blood plasma was developed using a Develosil C85 micron reverse phase column and a potassium dihydrogen phosphate buffer/acetonitrile mobile phase. Phenytoin and mephenytoin as an internal standard were detected by ultraviolet absorbance at 240 nm. The sample preparation method involves a rapid and simple procedure based on solid-phase extraction using a C18-bonded phase. Phenytoin could be determined in the concentration range of 0.05-3 micrograms ml-1. The recovery of phenytoin added to human breast milk and plasma were 91.6-94.7 and 91.6-96.0%, respectively, with coefficient of variation less than 4.2 and 8.7%. The method has been used for drug level monitoring in the human breast milk, maternal plasma and cord blood plasma samples that were taken from patients treated with phenytoin. The average ratio between the breast milk concentrations versus the plasma concentration was 0.28 +/- 0.1, with a rather poor correlation (r = 0.3033).