Article Text
Abstract
Techniques are now available for estimating the plasma concentration of several drugs used in psychiatry. These techniques are clearly important for research but they can hardly be expected to improve the clinical management of patients unless the estimation is sensitive, reliable and reasonably quick; the method should be specific for the particular drug but should also specifically estimate any active metabolites. Even when reliable figures have been obtained, much more information is needed before they can be interpreted. The relationship between plasma (or plasma water) concentration and relevant tissue concentration (e. g. in the brain) must be known. Plasma samples should be taken at appropriate times, e. g. after the attainment of ‘steady-state’ conditions: plasma and tissue levels will then be in equilibrium. Diagnoses must be soundly based if inferences are to be drawn. Reliable methods of assessing clinical response must be available. These requirements pose difficult problems in psychiatry.