Rapid Measurement of Anticonvulsant Drug Concentrations in the Out-Patient Clinic, Using HPLC with Direct Injection of Plasma

Abstract

A manual column-switching technique is described for the measurement of phenytoin, phenobarbitone, carbamazepine, and carbamazepine 10,11-epoxide. The analytical system is designed to be portable for use at the out-patient clinic and comprises an isocratic pump, UV detector and injection valve, together with a preparation column. Diluted plasma or serum is injected, without pre-extraction, onto a preparation column which replaces the sample loop on the injection valve. After washing unwanted material to waste, the preparation column is switched in-line with the analytical column, where separation of analytes occurs. The precision, accuracy and carryover of this extra-laboratory system are comparable with those obtained with laboratory-based immunoassay systems. Operation of the system allows the reporting of results within 5 min of sample injection and requires no specialist skills. The technique should be of particular interest to district general hospital laboratories where workload does not justify the cost of an automated HPLC system as the total capital cost is comparable to that of a portable glucose analyser. In contrast to immunoassay systems consumable costs are minimal. The equipment is easy to transport and may be used in the out-patient department to provide an analytical service similar to that provided for the determination of prothrombin time at the anticoagulant clinic.