Editorial preface

International Journal of Clinical Pharmacy, Dec 1979

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Editorial preface

For several years past the quality control of serum drug level determinations has attracted much attention. Not only reliable, from day to day reproducible results must be obtained by each laboratory, but also different laboratories must obtain comparable results: accuracy and precision are required. The value of drug level determinations for clinical practice depends heavily on the fulfilment of these requirements. At the last FIP-congress at Brighton this point was stressed by several speakers. With the rising demand f o r drug level determinations the need for quality control became evident. In 1974 DIJKHUISin the Netherlands developed his serum preparation for a regular interlaboratory quality control programme for antiepileptic drugs. One of the aims of a programme of this type, a critical comparison of assay methods, was attained in the same year on a small scale with 15 cooperative laboratories, 6 antiepileptic drugs, each in i concentration, and 3 assay methods (based on GLC, spectrophotometry or spectrofluorometry). The results were published in this journal [DUKHUIS, I. C. (1975) Pharm. Weekblad I i o , 1177-1199 ]. Such a review, however, cannot provide more than a snapshot. New drugs become available, new laboratories participate in the control programme and new assay techniques are applied. A logical continuation of the first investigation, which might be regarded as a pilot experiment, was to attempt to organise an interlaboratory survey on a larger scale and to prepare a new appraisal of existing assay methods. In a large scale investigation with many participating laboratories methods which are not frequently used, may appear also in the collected material in sufficient number to allow a distinction to be made between deviating laboratories and deviating assay methods. Preparatory contacts between DIJKHUIS, PIPPENGER and RICHENS took place from 1977. These formed the basis on which the 1 9 7 8 - survey could be organised. About 640 laboratories from all over the world participated in it. It was carried out with 8 antiepileptic drugs - including i metabolite, each in 3 concentrations. The assay methods used proved to be based on 6 different principles, I-IPLC,RIA and EMIThaving been introduced in recent years. The results of this investigation with a critical discussion of the assay methods are published in the first article of this issue of the Scientific Edition. The second paper by DIJKHUIS,DE FLINES and RENGERINKgives an account of the preparation and the analysis of the serum which was used. Its quality is decisive for the whole investigation. In the fourth paper by HAGENAAR and DE JONG a short description is given of the processing of the test results. Of the remaining articles devoted to quality control the first by RICHENSdescribes his continuous international quality control programme and refers to the American programme installed by PIPPENGER. The second paper by JANSEN, one of the pioneers in the field of q u a l i t y control in clinical chemistry, describes the Dutch interlaboratory quality control programme in clinical chemistry. It is to be expected that much can be learned from the experience acquired in this discip!ine [see for instance also the recent paper by STAMM, J. Clin. Chem. Clin. Biochem. (1979) 17, 283297]. One must realise that a whole quality control programme for drug level determinations can be outlined, comprising the choice of the body fluid to be analysed, time and frequency of sampling, technique of sampling up to the presentation of the results. Only one of the last steps, the actual drug determination, is now under discussion. For a review of the very first question, when serum drug levels should b e monitored, the reader is referred to a recent paper by RICHENS and WARRINGTON [Drugs (1979) z7, 488-500]. Insofar as the antiepileptics are drugs, of which serum levels have been determined for a long time and also very frequently, it is correct that the international survey described concerns this group of drugs. With a view to the above mentioned changing circumstances regarding drugs, laboratories and techniques, a repetition at a certain time might be desirable. For other drugs, for instance cardio-active drugs, theophylline, lithium, tricyclic antidepressants, aminoglycoside antibiotics, a similar survey seems to be very useful also, though in some cases much attention must still be given to the complicating role oftherapeutically active drug metabolites. The paper by RICHEr~Sdraws attention to yet another problem, the use of different units in presenting the results, viz. in /~mol/1 versus /zg/ml or mg/l. The use of the mole as unit of amount of substance is often accepted in clinical chemistry or in the process of being accepted. Probably because in diagnostics the results of chemical determinations (expressed in mol/1) are compared with reference values expressed in the same unit, the changing of mass units to units of amount of substance, presents no special problem. In therapeutics, however, the results of drug level determinations will be compared to the administered dose of the drug. So long as drug dosage is expressed i n mass units, the danger of confusion exists. In his recent paper on achieving comparable analytical results from a n u m b e r of laboratories, WILSON[Analyst (1979) zo4, 273289] drew attention to the possibility of mistakes, occuring through the use of different units in result reporting. Finally the Editorial Board expresses the wish that the presentation of the comparison of assay methods will stimulate those who are concerned with quality control of drug level determinations to review their own methods critically and, if necessary, not to hesitate to move towards more accurate and precise methods, guided by the experience of others.


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Editorial preface, International Journal of Clinical Pharmacy, 1979, 1169-1170, DOI: 10.1007/BF02293427