Automated on-line dialysis, trace enrichment and high-performance liquid chromatography. Inhibition of interaction with the dialysis membrane and disruption of protein binding in the determination of clozapine in human plasma.
Problems related to interaction of drugs with the dialysis membrane and to protein binding must be overcome in order to develop automated methods for drug analysis based on on-line dialysis, trace enrichment and HPLC. In order to study these problems, clozapine and its active metabolite N-desmethylclozapine were chosen as model compounds because they were found to interact with the dialysis membrane, and clozapine is highly protein bound. Addition of a cationic surfactant, dodecylethyldimethyl ammonium bromide, to the donor solution and to the plasma samples was found to inhibit interaction of the drugs with surfaces. The protein binding in plasma was disrupted prior to dialysis by lowering the pH with hydrochloric acid and the plasma proteins were solubilised with glycerol. The results obtained were used to develop a fully automated method for the determination of clozapine and N-desmethylclozapine in human plasma. More than 100 samples could be analysed within 24 h. The limit of detection in human plasma was 0.050 mumol/l for clozapine and 0.055 mumol/l for N-desmethylclozapine. Linearity was found for drug concentrations between 0.25-3 mumol/l. The relative standard deviations were between 1.2-6.7% and the method was applicable for therapeutic drug monitoring.
Johansen
K
K
School of Pharmacy, University of Oslo, Norway.
Krogh
M
M
Rasmussen
K E
KE
D014150:Antipsychotic Agents / Q000097:blood* / Q000737:chemistry / Q000378:metabolism; D001798:Blood Proteins / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003024:Clozapine / Q000031:analogs & derivatives / Q000097:blood* / Q000737:chemistry / Q000378:metabolism; D003956:Dialysis / Q000295:instrumentation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008567:Membranes, Artificial; D011485:Protein Binding; D015203:Reproducibility of Results
D014150:Antipsychotic Agents; D001798:Blood Proteins; D008567:Membranes, Artificial; C058272:norclozapine; D003024:Clozapine