Selection of analytic methods for therapeutic drug monitoring

Selection of an analytic method for therapeutic drug monitoring usually involves an initial choice between chromatography and immunoassay. Once this decision has been made, numerous options remain within these two broad categories. There is no single correct or preferred assay technique. The best decision, based on technical, clinical, and economic considerations, will vary in different clinical and laboratory environments. The laboratory that has sufficient resources to maintain more than one type of technology will have a greater degree of flexibility in solving special problems.

Sustained ventricular tachycardia after repair of tetralogy of Fallot: new electrophysiologic findings

Ventricular arrhythmia originating from the outflow tract of the right ventricle is a presumed cause of late sudden death in patients after repair of tetralogy of Fallot. Exercise testing has been shown to enhance detection, and phenytoin has been shown to control ventricular arrhythmias in these patients. This study reports new findings in 3 patients who underwent electrophysiologic studies at postoperative cardiac catheterization; in each, sustained ventricular tachycardia was induced and found to originate from the inflow-septal area of the right ventricle. Using serial studies, the same sustained ventricular tachycardia was induced during therapeutic serum concentrations of phenytoin but not after propranolol. No patient had ventricular arrhythmia during a 24-hour electrocardiogram or during exercise. Although no patient had normal hemodynamic function, only 1 patient had right ventricular pressure greater than two-thirds systemic pressure. Each patient had undergone initial intracardiac repair at a relatively late age (3, 9, and 9 years).

EMIT antiepileptic drug assays adapted to an Abbott-VP Analyzer and compared with a gas-chromatographic procedure

The Abbott-VP Bichromatic Analyzer was used for the determination of four antiepileptic drugs (phenobarbital, phenytoin, carbamazepine, primidone) in serum by means of a modified EMIT homogeneous enzyme immunoassay procedure. The main objective of the work was to examine the precision and the accuracy of the results obtained with this system and its cost effectiveness in comparison to the manual method. Day-to-day precision for all four drugs is excellent with coefficients of variation averaging around 5% in the therapeutic range of concentrations. Results for sera analyzed by this procedure and by a gas chromatographic method do not show any significant difference for phenytoin and phenobarbital. There are however slight differences between the two methods for carbamazepine and primidone. These small differences do not modify significantly the clinical interpretation of the results. The procedure is simple and rapid, and requires only one third of the reagents needed in the recommended manual EMIT procedure using the Gilford Stasar III, thus greatly reducing the operation costs.

Enzyme immunoassays in clinical chemistry: present status and trends

The most important enzyme immunoassay techniques are described. The enzymes currently used as labels, the methods of coupling them to antigens or haptens and the possible applications of these assays are reviewed. Furthermore, an overview is given of the reliability and practicability of commercially available enzyme immunoassay kits used in clinical chemical laboratories. Special consideration is given to possible interferences, the detection limits and the mechanization of these tests. Various methods for curve-fitting are listed. It is concluded that most of the currently commercially available enzyme immunoassays are suitable for routine application in appropriate centers like clinical chemical laboratories of larger hospitals. The future role of enzyme immunoassays in clinical chemistry is briefly discussed.

Rapid, reproducible enzyme immunoassay for gentamicin

An enzyme immunoassay for gentamicin utilizing glucose-6-phosphate dehydrogenase was compared to the radioimmunoassay. The enzyme immunoassay for gentamicin was accurate, specific, and easily performed. It offers an ulternative method to assay aminoglycosides and could be used in institutions using enzyme immunoassay to assay other drugs.

The treatment of severe drug intoxication with charcoal hemoperfusion in series with hemodialysis

Two patients were treated for serious phenobarbital intoxication with charcoal perfusion and hemodialysis in series. Both patients experienced decreases in coma, but both of them bled after treatment. Phenobarbital levels were decreased to 50% with treatments, and there was not any significant difference of the clearance for the two devices.

Enzyme multiplied immunoassay of phenytoin and carbamazepine using the Centrifichem analyser

Procedures for the enzyme multiplied immunoassay of phenytoin and carbamazepine using the Centrifichem centrifugal analyser are described. Within-batch, between-batch, and between-day precision are reported. Accuracy is assessed by recovery experiments. The technique is compared with gas-liquid chromatography in the analysis of a number of human serum samples containing a range of concentrations of the drugs.

Automation of diphenylhydantoin and phenobarbital measurements using the ABA-100 with emit reagents

1. The EMIT-AED procedures for phenobarbital and diphenylhydantoin have been adapted for use on the ABA-100. 2. A basic language computer program has been developed for data reduction and quality control. 3. Within-run and run-to-run coefficients of variations were, in general, less than 8% across the concentration range tested. 4. Performance data on agreement of duplicates and recovery from "spiked" samples were aceptable. 5. The automated procedure provides a two-thirds savings in reagents.

Enzyme multiplied immunoassay technique: a review

A brief review of the various immunoassays is presented before the basic mechanism of the enzyme multiplied immunoassay technique (EMIT) is described. This is followed by a presentation of the specific advantages and disadvantages of this method, as well as its correlation with other methods as applied to qualitative and quantitative determinations of each type of drug for which EMIT technology is available.

Determination of phenobarbital and phenytoin in serum by a mechanized enzyme immunoassay (EMIT) in comparison with a gas-liquid chromatographic method

The antiepileptic drugs phenobarbital and phenytoin were determined in serum by enzyme immunoassay (Emit, Syva Corp.) and gas-liquid chromatography. The Emit assays were mechanized by the use of an Eppendorf analyzer 5010. The precision of the Emit system was sufficient (coefficient of variation within series 6-13% and from day to day 8-15% with various calibrators and control sera). Moreover the Emit method is rapid, specific and easy to perform. The procedure requires only 10 microliter of serum per determination. A disadvantage however is the high cost of the reagents. A comparison of the results obtained by Emit and gas-liquid chromatography in a series of about 50 patients showed a good correlation between both methods (correlation coefficient r = 0.968 for phenobarbital and 0.978 for phenytoin).