HPLC determination of tramadol in human breast milk

Tramadol is a centrally acting analgesic used for prevention and treatment of moderate to severe pain. It is estimated that 0.1% of the administered dose passes into breast milk causing potentially unwanted effects in nursing babies. Pharmacokinetically, breast milk is supposed to be a separate compartment into which the drug is excreted-mainly by passive diffusion. Due to a complex composition of breast milk, a suitable sample preparation procedure is needed with a subsequent chromatographic analysis for drug determination. Among several sample cleanup procedures tested we chose the liquid-liquid extraction procedure using n-hexane as an organic phase with back extraction into aqueous phase since it was considered the most suitable and the most compatible with the subsequent HPLC analysis. The precision and the reproducibility of the method were improved approximately two times by using metoprolol as an internal standard thus making the method also more robust with regard to a variable composition of milk samples. These characteristics, together with low detection limit and short analysis time, proved that the developed method is suitable for monitoring of tramadol in human breast milk.