Simultaneous determination of clobazam, N-desmethyl clobazam and clonazepam in plasma by high performance liquid chromatography.

A method is described for the simultaneous determination of clobazam, its active metabolite N-desmethylclobazam, and clonazepam in plasma by high performance liquid chromatography. The drugs are extracted with diethyl ether from 1.0 ml plasma adjusted to pH 9.0 and separated on a C18 reverse phase column using a mobile phase of 40% acetonitrile in phosphate buffer pH 3.0. The ultraviolet absorbance is monitored at a wavelength of 313 nm. The method has a coefficient of variation of less than 5% and an overall recovery of greater than 85% and is sufficiently sensitive for the therapeutic monitoring of these drugs.