A laboratory can validate a method to measure two medicines in a combination tablet. Applying the same method to blood introduces a new specimen with different potential interferences. Ashour and Kattan developed a high-performance liquid chromatography method for clidinium bromide and chlordiazepoxide in pharmaceutical preparations.
The researchers used a reversed-phase C8 column, ultraviolet detection and almotriptan as an internal standard. They separated the two ingredients from one another and checked accuracy, precision, linearity and robustness. The chromatogram from the tested tablet preparation showed clear separation of the drug peaks, without an observed interference from the tablet excipients under those conditions.
Tablet recovery and separation support a conclusion about the preparations the investigators tested. A blood or urine method would have to address endogenous compounds, extraction losses and potentially interfering drugs or metabolites in that specimen. In a laboratory review, match the stated detection limit and selectivity to the actual sample and method. Figures established for a tablet extract should be interpreted within that analytical setting.