Application of coated green source carbon dots with silica molecularly imprinted polymers as a fluorescence probe for selective and sensitive determination of phenobarbital

Herein, a selective and sensitive fluorescence sensor was developed for the detection of phenobarbital, an epilepsy drug, using molecularly imprinted polymers (MIPs) coated on the surface of green source carbon dots (GSCDs). First, GSCDs were synthesized through a hydrothermal method using Cedrus as a carbon source. Then, a MIPs-GSCDs as a fluorescence probe was obtained by coating a thin film of silica on the surface of the GSCDs using a reverse micro emulsion method. In this step, phenobarbital, 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) were applied as a template, a functional monomer, and cross linker, respectively. The fluorescence signal of MIPs-GSCDs was selectively quenched by phenobarbital rebinding with MIP cavities. The fluorescence quenching signal was applied for phenobarbital sensing at the pH = 8 without the interference of other materials. After optimizing the factors affecting the sensor's response, a linear range between 0.4 and 34.5 nmol L^-1 with a detection limit of 0.1 nmol L^-1 was obtained. The sensor's capability in the real sample analysis was investigated by phenobarbital determination in a human blood plasma samples.

Phenobarbital loaded microemulsion: development, kinetic release and quality control

ABSTRACT This study aimed to obtain and characterize a microemulsion (ME) containing phenobarbital (PB). The PB was incorporated in the proportion of 5% and 10% in a microemulsion system containing Labrasol(r), ethanol, isopropyl myristate and purified water. The physicochemical characterization was performed and the primary stability of the ME was evaluated. An analytical method was developed using spectrophotometry in UV = 242 nm. The kinetics of the in vitro release (Franz model) of the ME and the emulsion (EM) containing PB was evaluated. The incorporation of PB into ME at concentrations of 5 and 10% did not change pH and resistance to centrifugation. There was an increase in particle size, a decrease of conductivity and a change in the refractive index in relation to placebo ME. The ME remained stable in preliminary stability tests. The analytical method proved to be specific, linear, precise, accurate and robust. Regarding the kinetics of the in vitro release, ME obtained an in vitro release profile greater than the EM containing PB. Thus, the obtained ME has a potential for future transdermal application, being able to compose a drug delivery system for the treatment of epilepsy.

An ImmunoChip prototype for simultaneous detection of antiepileptic drugs using an enhanced one-step homogeneous immunoassay

The development and characterization of a one-step homogeneous immunoassay-based multiwell ImmunoChip is reported for the simultaneous detection and quantitation of antiepileptic drugs (AEDs). The assay platform uses a cloned enzyme donor immunoassay (CEDIA) and a Beta-Glo assay system for generation of bioluminescent signal. Results of the one-step CEDIA for three AEDs (carbamazepine, phenytoin, and valproic acid), in the presence of serum, correlate well with the values determined by fluorescence polarization immunoassay. CEDIA intra- and interassay coefficients of variation are less than 10%. A microfabrication process, xurography, was used to produce the multiwell ImmunoChip. Assay reagents were dispensed and lyophilized in a three-layer pattern. The multiwell ImmunoChip prototype was used to detect and quantify AEDs in serum samples containing all three drugs. Luminescent signals generated from each well were recorded with a charge-coupled device (CCD) camera. The assays performed on an ImmunoChip were fast (5 min), requiring only small volumes of both the reagents (<1 microl/well) and the serum sample. The ImmunoChip assay platform described in this article may be well suited for therapeutic monitoring of drugs and metabolites at the point-of-care setting.

Immunological studies on delayed hypersensitivity to phenytoin--I. A new method for preparing phenytoin antiserum

The present study was initiated to produce an antiserum to phenytoin with high specificity and sensitivity which would be suitable not only for determination of blood phenytoin concentration but also for induction of a hypersensitivity reaction to phenytoin in experimental animals. p-Aminophenytoin was synthesized and identified by means of IR, 1H-NMR and mass spectroscopy. BSA-phenytoin conjugate was prepared by using p-aminophenytoin, BSA and, as a coupling reagent, glutaraldehyde. Satisfactory response to immunization was achieved at a 9.8:1 molar ratio of p-aminophenytoin to BSA. The antiserum obtained from rabbits immunized with BSA-phenytoin conjugate exhibited practically no cross-reactivity with either phenytoin metabolites or other anti-epileptic drugs, indicating that this antiserum provides sufficiently high specificity. In our experiments, the lower limit for detecting phenytoin was 2 ng using RIA, whereas 200 ng was the minimum amount detectable by HPLC. Thus, by a difference of two orders of magnitude, the present RIA method shows a much higher sensitivity than that of HPLC, though we found a good correlation of simultaneous determinations of serum phenytoin between the two methods. Reproducibility of phenytoin determination in plasma was confirmed by calculating the coefficient of variance. The values were less than 10%.

[Simultaneous determination of 4 anticonvulsant drugs by high pressure liquid chromatography (HPLC)]

We describe a sensitive and precise method for the simultaneous high pressure liquid-chromatography determination of phenobarbital, diphenylhydantoin, primidone, and carbamazepine in serum. The drugs are extracted into chloroform, dried and dissolved in the mobile phase. The drugs are eluted from a reverse-phase column with methanol/water and detected by their absorption at 214 nm. Concentrations are estimated from their peak heights. The results, when compared with those by enzyme-immunoassay, gave correlation coefficients of 0.990 for phenobarbital, 0.993 for diphenylhydantoin, 0.992 for primidone and 0.994 for carbamazepine.

Evaluation of the bioavailability of a solid dispersion of phenytoin in polyethylene glycol 6000 and a commercial phenytoin sodium capsule in the dog

In this study a solid dispersion of phenytoin in polyethylene glycol 6000 was prepared by the melt method. The content uniformity of the dispersion indicated a range of 98.7-102.0%. X-ray crystallographic data showed no changes in the crystalline structure of the phenytoin in the dispersion when compared with that in the bulk reagent. Scanning electron micrographs of the dispersion show a reduction in the size of the crystals when compared with the bulk reagent. The commercial product and the dispersion were compared using the USP criteria for the prompt phenytoin sodium dissolution test. The salt dissolved at a rate four times greater than the dispersion. Bioequivalency comparisons between the dispersion containing phenytoin and the commercial prompt phenytoin sodium were studied in six mixed-breed dogs. All samples were analyzed using a commercial enzyme immunoassay system. Statistical analysis of the plasma levels obtained from the animal studies indicate no significant differences (p greater than 0.05) between area under the curve, maximum plasma concentration, and time to peak for the commercial salt and the acid formulation.

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.

Elevated serum phenytoin concentrations in a uremic patient when measured by enzyme-multiplied immunoassay

A patient with chronic renal failure did not respond to "therapeutic" serum phenytoin concentrations as measured by enzyme-multiplied immunoassay (EMIT). Her seizure disorder was not controlled despite phenytoin concentrations of 25-35 micrograms/ml. When her serum samples were reassayed by high pressure liquid chromatography and gas-liquid chromatography, the phenytoin serum concentrations were found to be approximately 1/2 of the previously reported values, that is, 16.0 micrograms/ml vs. 33 micrograms/ml. The precise reason for this discrepancy is currently unknown. Our findings suggest that the EMIT assay may yield falsely elevated serum phenytoin concentrations in uremic subjects.

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.

Accuracy of serum anticonvulsant measurements. A comparison of enzyme multiplied immunoassay technique and gas-liquid chromatography

An enzyme multiplied immunoassay technique is compared with a gas-liquid chromatographic technique for the measurement in blood serum of the anticonvulsants phenytoin, carbamazepine, phenobarbitone, primidone, and ethosuximide. The correlation between results obtained by each method was excellent, and both systematic and random errors were well within acceptable limits.

Enzyme immunoassay of theophylline with the Abbott ABA-100

The enzyme immunoassay of theophylline using the "EMIT" reagents was adapted to the Abbott ABA. The method greatly increases the maximum tests per kit. The correlation with high pressure liquid chromatography was 99%. No interference with bilirubin was found at 15 mg/dl. of total bilirubin. The method is useful for pediatric patients including newborns.

A micromethod for simultaneous estimation of blood levels of some commonly used antiepileptic drugs

The analysis of serum samples for the antiepileptic drugs carbamazepine, phenobarbital and phenytoin by a simple extraction technique and chromatographic analysis by high-pressure liquid chromatography is described. The method is a micro one which correlates well with gas-liquid chromatographic procedures. Coefficients of variation are smaller than 3%.

Rapid and micro high-pressure liquid chromatographic determination of plasma phenytoin levels

A rapid and simple high-pressure liquid chromatographic microanalytical method was developed for the determination of clinically encountered plasma phenytoin levels. This method is accurate down to about 1 microgram of phenytoin/ml of plasma and requires as little as 10 microliter of sample. Total analysis time is about 10 min. The method involves deproteinizing with acetonitrile followed by monitoring the deproteinized sample at 254 nm. Phenytoin's primary metabolite in humans, 5-(p-hydroxyphenyl)-5-phenylhydantoin, also can be quantitated when present in moderately high clinically encountered concentrations. Plasma profiles of phenytoin and its metabolite were followed with time after an intravenous bolus injection to a rabbit.

Simultaneous determination of diphenylhydantoin, mephobarbital, carbamazepine, phenobarbital and primidone in serum using direct chemical ionization mass spectrometry

A quantitative method for the simultaneous determination of five anticonvulsants in serum has been developed using chemical ionization mass spectrometry without prior chromatographic separation. The technique was shown to be rapid, simple and sensitive, allowing the routine analysis of 50 microliter of serum with good within-day and day-to-day precision.

A comparison of the "EMIT" assay with two iodinated radioimmunoassays for diphenylhydantoin

In the treatment of epilepsy, it is important for the laboratory to provide blood diphenylhydantoin levels accurately and quickly. However, physicians have often obtained laboratory results which have been inconsistent with the patient's clinical condition. We examined the "Enzyme Multiplied Immuno Technique" (EMIT) and two iodinated radioimmunoassay procedures for their suitability to provide quick and accurate blood diphenylhydantoin levels in laboratories that perform relatively few assays. The results indicated that all three procedures can be used with reasonable success. We found that the simplicity and the long shelf-life of the EMIT procedure made it very desirable for institutions that have a small volume of diphenylhydantoin assays.

Determination of phenytoin in plasma: a comparison of procedures using a new radioimmunoassay, gas chromatography, and enzyme immunoassay

A new commercially available radioimmunoassay (RIA) procedure for the anticonvulsant drug phenytoin has been assessed and compared with a gas-liquid chromatographic (GLC) and an enzyme immunoassay (EMIT) procedure. One hundred and thirty-four plasma samples containing phenytoin were analyzed by the three methods and the results were found to be essentially independent of the procedure used and so would indicate similar clinical interpretation. The correlation coefficients were: RIA/GLC = 0.988; EMIT/RIA = 0.978; EMIT/GLC = 0.981. The cross reactivity of 33 drugs and related compounds was tested in the RIA and EMIT procedures and only a few very closely related substances showed significant cross reactivity. In addition, the three methods were compared with respect to the technical difficulties involved as well as time and cost for the assay of single and multiple samples.

Comparison of the EMIT test with high-performance liquid chromatography for the determination of phenobarbital in serum

The new enzyme immunoassay technique (EMIT) is compared to high-performance liquid chromatography used for determining phenobarbital in serum. After resuming the methods of both techniques, we compare the results of 116 sera collected from patients receiving treatment for epilepsy. The equation of the correlation curve is: HPLC = 0.98 EMIT + 0.12. The reliability characteristics are comparable. The enzyme immunoassay technique is less specific but more practicable.

Correlation of the "EMIT" with a gas-liquid chromatographic method for determination of antiepileptic drugs in plasma

We report a study of the comparison of antiepileptic drugs (phenobarbital, phenytoin, primidone, and carbamazepine) by the Enzyme Multiplied Immunoassay Technique "EMIT" and the gas chromatography (GLC) method. Overall, reasonable correlations were observed for all of the above-mentioned assays by both methods in the majority of samples included in this study. Our observations for statistical and clinical differences at various levels of phenobarbital and phenytoin are discussed. A suggestion is provided in order to avoid a major discrepancy (approximately 30% higher values by EMIT vs GLC) in results observed from the "Bottom of the Bottle Effect" for EMIT reagent.

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.

Enzyme multiplied immunoassay of phenobarbital by LKB reaction Rate Analyser: a comparison with analysis by gas-liquid chromatography

A procedure for the enzyme multiplied immunoassay of phenobarbital using the LKB Reaction Rate Analyser is described. The temperature optimum, linearity, specificity, and precision of the assay are reported. A highly significant correlation coefficient is obtained when the technique is compared with gas-liquid chromatography by analysing human sera containing a range of phenobarbital levels.

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).

Drug screening by enzyme immunoassay (EMIT) and thin-layer chromatography (Drug Skreen)

Urine samples (n = 300) were examined for drugs by thin-layer chromatography ("Drug Skreen", Brinkmann Corp.) and by the "Enzyme Multiplied Immunoassay Technique" ("Emit", Syav Corp.). The results of both methods were compared for the detection of opiates, barbiturates and amphetamines. In more than 90% of the determinations identical results were obtained with both methods. About 10% of the results of the Emit barbiturate assay differed from those of thin-layer chromatography and therefore had to be further investigated by gas liquid chromatography. It could be demonstrated that the barbiturate determination by the Emit system correlated better with the results of gas liquid chromatography. From the results of this study it is suggested that thin-layer chromatography is used as a screening test, and to confirm positive results with other methods such as Emit. If the abuse of barbiturates or opiates is suspected the corresponding Emit test should also be performed, even in cases of a negative thin-layer chromatography screening. Confirmation with a third method such as gas liquid chromatography is necessary, if thin-layer chromatography and Emit lead to divergent results.