CN116298257A

CN116298257A - Phenytoin detection kit

Info

Publication number: CN116298257A
Application number: CN202310364997.8A
Authority: CN
Inventors: 龚俊; 祁金祥; 张启飞; 肖兰萍; 王贵利; 刘希
Original assignee: Beijing Strong Biotechnologies Inc
Current assignee: Beijing Strong Biotechnologies Inc
Priority date: 2019-01-09
Filing date: 2019-12-31
Publication date: 2023-06-23
Also published as: CN111504920A; CN111693473A; CN116699122A; CN111537452B; CN112285037B; CN111504920B; CN116698772A; CN116699125A; CN116679047A; CN111650135B; CN116381253A; CN116298330A; CN116718761A; CN111487208B; CN116773795A; CN116430056A; CN116338215A; CN116559425A; CN111239060B; CN116840467A

Abstract

The present application relates to phenytoin assay kits. In particular, the mutant glucose 6-phosphate dehydrogenase of the present application comprises one mutation compared to the wild-type glucose 6-phosphate dehydrogenase selected from the group consisting of: d306C, D375C, G426C. The detection kit prepared by using the glucose 6-phosphate dehydrogenase mutant has the advantages of strong specificity, high sensitivity, convenient operation, short detection time, accurate quantification and suitability for high-throughput detection.

Description

Phenytoin detection kit

The application is a divisional application of Chinese patent application No. 201911403882.5 (application date 2019, 12, 31) of 6-phosphoglucose dehydrogenase mutant and application of the mutant in preparation of phenytoin detection reagent.

Technical Field

The application relates to the field of biological detection, in particular to a multi-site mutant enzyme glucose 6-phosphate dehydrogenase (G6 PDH for short) and application thereof in a phenytoin detection kit.

Background

Hapten, some small molecule substances (molecular weight less than 4000 Da) alone are not able to induce an immune response, i.e. are not immunogenic, but are immunogenic when crosslinked or conjugated to a carrier such as a macromolecular protein or non-antigenic polylysine, inducing an immune response. These small molecule substances can bind to the response effect products, are antigenic, are only immunoreactive, are not immunogenic, and are also called incomplete antigens.

Hapten can bind to the corresponding antibody to generate antigen-antibody reaction, and antigen which can not independently excite human or animal body to generate antibody can not be generated. It is only immunoreactive, not immunogenic, also known as incomplete antigen. Most polysaccharides, lipids, hormones and small molecule drugs belong to the hapten group. If hapten is chemically bound to a protein molecule (carrier), new immunogenicity is obtained and the animal is stimulated to produce the corresponding antibody. Hapten, once bound to a protein, constitutes an antigenic cluster of the protein. Some chemically active substances (such as penicillin, sulfonamides, etc.) which have a smaller molecular weight than the general hapten but a specific structure are called simple haptens.

Small molecule antigens or haptens, which lack two or more sites available for sandwich methods, cannot be assayed by the double antibody sandwich method, and are often in competition mode. The principle is that the antigen in the specimen and a certain amount of enzyme-labeled antigen compete for binding with the solid phase antibody. The more the antigen content in the specimen, the less the enzyme-labeled antigen is bound on the solid phase, and the lighter the color development. ELISA assay for small molecule hormones, drugs and the like is commonly used.

Phenytoin (PTN), a specific example of hapten, is an antiepileptic exogenous small molecule drug. This substance is not present in serum or plasma of normal humans, and is generally used clinically in the form of its sodium salt.

Phenytoin sodium as traditional antiepileptic drug with pharmacological action mechanism mainly of blocking voltage dependence Na ⁺ Channels, reduce Na ⁺ The influx stabilizes the neuronal cell membrane, reducing its excitability, thereby preventing the diffusion of local abnormal discharges into normal brain tissue.

The phenytoin sodium reaches peak concentration 1.5 to 30 hours after oral administration, and the effective blood concentration can be reached after continuous administration for 6 to 10 days generally, and the phenytoin sodium has low price and definite curative effect and is widely used in clinic at present. However, due to the special pharmacokinetics, the treatment window is narrow, excessive drug is easy to poison, clinical manifestations after poisoning are various, and misdiagnosis is easy. Therefore, during clinical diagnosis, it is necessary to constantly monitor the concentration of phenytoin in blood.

Usually, the blood concentration can reach the optimal treatment effect at 10-20 mug/ml, and the drug does not have toxic and harmful effects on human bodies. When the blood drug concentration is higher than 20 mug/ml, the drug can cause toxicity to the liver and the kidney of a human body, and the patient is in coma and die in severe cases. Generally, the blood concentration of phenytoin can be reduced to a level of 0.5 μg/ml or less after stopping administration for 2-4 weeks and metabolizing via human liver and kidney.

The currently known methods for detecting phenytoin mainly comprise: enzyme-linked immunosorbent assay, homogeneous enzyme immunoassay, chemiluminescent immunoassay, high performance liquid chromatography, fluorescence polarization method, etc. However, the detection methods have many defects, such as radioactive pollution, short effective period, inconvenient operation and the like of radioimmunoassay isotopes, and the ELISA method has the defects of complicated operation, long time consumption and inapplicability to clinical use. The chemiluminescence has better sensitivity, but needs matched special equipment, and has higher input use cost and is not beneficial to popularization. In clinical detection and diagnosis, homogeneous enzyme immunoassay (EMIT) is the dominant method.

Principle of homogeneous enzyme immunoassay: in a liquid homogeneous reaction system, enzyme-labeled antigen (such as G6 PDH-phenytoin) and unlabeled antigen (phenytoin) compete for being combined with quantitative antibody (phenytoin antibody), when the more the antibody is combined with unlabeled antigen, the more the activity of the enzyme-labeled antigen is released, the more the enzyme-catalyzed substrate NAD+ generates NADH, and the absorbance change of NADH is detected at the wavelength of 340nm, so that the phenytoin content in the liquid can be deduced.

Disclosure of Invention

In view of the needs in the art, the present application provides a novel glucose 6-phosphate dehydrogenase mutant and its use in preparing phenytoin assay kits.

According to some embodiments, a glucose 6-phosphate dehydrogenase mutant is provided. Unlike the mutants of glucose 6 phosphate dehydrogenase of the prior published patent US006090567A (Homogeneous immunoassays using mutant glucose-6-phosphate dehydrogenases), the glucose 6-phosphate dehydrogenase mutants of the present application comprise a mutation selected from the group consisting of: d306C, G426C, D375C.

According to some embodiments, there is provided a glucose 6-phosphate dehydrogenase mutant, the glucose 6-phosphate dehydrogenase mutant being represented by a sequence selected from the group consisting of: SEQ ID No.2, SEQ ID No.3, SEQ ID No.4.

According to some embodiments, a polynucleotide encoding a glucose 6-phosphate dehydrogenase mutant of the present application is provided.

According to some embodiments, there is provided an expression vector comprising a polynucleotide of the present application.

According to some embodiments, a host cell is provided comprising an expression vector of the present application. The host cell may be prokaryotic (e.g., bacteria) or eukaryotic (e.g., yeast).

According to some embodiments, there is provided a conjugate which is a glucose 6-phosphate dehydrogenase mutant of the present application and a hapten in a molar ratio of 1: and n is coupled.

In some embodiments, n is 1 to 50, e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50.

In some specific embodiments, the molar ratio of the glucose 6-phosphate dehydrogenase mutant to hapten of the present application is preferably 1:1.

in some specific embodiments, the hapten has a molecular weight of 100Da to 4000Da, for example: 100. 150, 200, 250, 300, 350, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 520, 550, 570, 600, 620, 650, 700, 750, 800, 850, 900, 950, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000.

In light of the present application, the skilled artisan will appreciate that "hapten" also includes the form of its derivative. In order to facilitate coupling with glucose-6-phosphate dehydrogenase, haptens (e.g., phenytoin) that do not themselves carry a coupling group (e.g., a group that reacts with a thiol group) may be engineered to carry a linker for covalent binding to the thiol group. Thus, in the present application, hapten derivatives refer to haptens engineered to bear a thiol-reactive group.

The hapten is selected from the group consisting of: small molecule drugs (e.g., antibiotics, psychotropic drugs), hormones, metabolites, sugars, lipids, and amino acids.

Hapten such as, but not limited to: phenytoin, vitamin D, 25 hydroxy vitamin D, 1, 25 dihydroxyvitamin D, folic acid, cardiac glycoside, zymophenolic acid, lei Paming, cyclosporin A, amiodarone, methotrexate, tacrolimus, serum amino acids, bile acids, glycocholic acid, phenylalanine, ethanol, uronikotin metabolite cotinine, uromorphine, uromonophenol derivatives, neuropeptide tyrosine, plasma galanin, polyamines, histamine, thyroid stimulating hormone, prolactin, placental lactation, growth hormone, follicle stimulating hormone, luteinizing hormone, adrenocorticotropic hormone, antidiuretic hormone, calcitonin, procalcitonin, parathyroid hormone, thyroxine, triiodothyronine, anti-triiodothyronine, free thyroxine, free triiodothyronine, cortisol, urine 17-hydroxycortisterol urinary 17-ketosteroid, dehydroepiandrosterone, sulfate, aldosterone, urovanillyl mandelic acid, plasma renin, angiotensin, erythropoietin, testosterone, dihydrotestosterone, androstenedione, 17 alpha hydroxy progesterone, estrone, estriol, estradiol, progesterone, human chorionic gonadotrophin, insulin, proinsulin, C peptide, gastrin, plasma prostaglandin, plasma 6-keto prostaglandin f1α, prostacyclin, epinephrine, catecholamine, norepinephrine, cholecystokinin, natriuretic acid, cyclic adenosine monophosphate, cyclic guanosine monophosphate, vasoactive peptide, somatostatin, secretin, substance P, neurotensin, thromboxane A2, thromboxane B2, 5 hydroxytryptamine, neuropeptide Y, osteocalcin.

In a specific embodiment, the hapten is phenytoin or a derivative thereof.

In a specific embodiment, the hapten is a phenytoin derivative bearing a sulfhydryl reactive group such as, for example, a maleimide, bromoacetyl, vinyl sulfone, or aziridine. In a specific embodiment, the hapten is a phenytoin derivative, as shown in formula I:

according to some embodiments, there is provided an agent comprising a conjugate of the present application.

According to some embodiments, there is provided the use of a glucose 6-phosphate dehydrogenase mutant of the present application in the preparation of a phenytoin detection reagent.

According to some embodiments, there is provided the use of a conjugate of the present application in the preparation of a phenytoin detection reagent.

In specific embodiments, the detection reagent is selected from the group consisting of: ELISA detection reagent, chemiluminescent detection reagent, homogeneous ELISA detection reagent and latex enhanced turbidimetry detection reagent.

In a specific embodiment, the detection reagent is preferably a reagent for competition-based detection.

According to some embodiments, there is provided a phenytoin detection kit comprising:

-a first reagent comprising a substrate and a phenytoin antibody; the substrate is a substrate for glucose-6-phosphate dehydrogenase;

-a second agent comprising a conjugate of the present application;

-optionally, a calibrator comprising 10mM to 500mM buffer, 0mg/L to 42mg/L phenytoin; and

-optionally, a quality control comprising 10mM to 500mM buffer, 0mg/L to 42mg/L phenytoin.

According to one embodiment, there is provided a phenytoin assay kit comprising:

a first reagent comprising:

10mM to 500mM buffer,

5mM to 25mM substrate,

0.1mg/L to 5mg/L phenytoin antibody,

10mM to 300mM NaCl,

0.1g/L to 5g/L of stabilizer,

0.1g/L to 5g/L of surfactant,

0.1g/L to 5g/L preservative;

a second reagent comprising:

10mM to 500mM buffer,

0.1mg/L to 1mg/L of a conjugate according to the present application,

0.1g/L to 5g/L of stabilizer,

0.1g/L to 5g/L of surfactant,

0.1g/L to 5g/L preservative.

In some embodiments, the buffer is selected from one or a combination of the following: tromethamine buffer, phosphate buffer, tris-HCl buffer, citric acid-sodium citrate buffer, barbital buffer, glycine buffer, borate buffer, tris buffer; preferably, a phosphate buffer; the concentration of the buffer is 10mmol/L to 500mmol/L, preferably 100mM; the pH of the buffer is 6-8, preferably 7.2 or 7.0.

In some embodiments, the stabilizer is selected from one or a combination of the following: bovine serum albumin, trehalose, glycerol, sucrose, mannitol, glycine, arginine, polyethylene glycol 6000, polyethylene glycol 8000; bovine serum albumin is preferred.

In some embodiments, the surfactant is selected from one or a combination of the following: brij35, triton X-100, triton X-405, tween20, tween30, tween80, coconut fatty acid diethanolamide, AEO7, preferably Tween20.

In some embodiments, the preservative is selected from one or a combination of the following: azide, MIT, PC-300, merthiolate; the azide is selected from: sodium azide and lithium azide.

In some embodiments, the substrate comprises: glucose-6-phosphate, beta-nicotinamide adenine dinucleotide.

In some embodiments, a method of preparing a conjugate is provided, comprising the steps of:

1) Providing a phenytoin derivative, preferably in an aprotic solvent;

2) Providing a glucose 6-phosphate dehydrogenase mutant as defined in claim 2, preferably providing said glucose 6-phosphate dehydrogenase mutant in a buffer;

3) Contacting said phenytoin derivative and said mutant glucose 6-phosphate dehydrogenase at 18 ℃ to 28 ℃ for 1 hour to 4 hours, preferably 2 hours to 3 hours, such that said phenytoin derivative and said mutant glucose 6-phosphate dehydrogenase are coupled to obtain said conjugate;

4) Optionally, purifying, preferably desalting, the conjugate;

steps 1) and 2) may be interchanged or parallel;

the buffer is selected from the group consisting of: PBS, tris, TAPS, TAPSO, the buffer pH is from 6.0 to 8.0;

the aprotic solvent is selected from one or a combination of the following: acetonitrile, dimethylformamide, dimethyl sulfoxide;

preferably, prior to step 3), the glucose 6-phosphate dehydrogenase mutant comprises a free thiol group; more preferably, the glucose 6-phosphate dehydrogenase mutant has a free thiol group at position 306, 375 or 426.

Drawings

FIG. 1 is a diagram of the structure of phenytoin.

FIG. 2 shows the structure of phenytoin derivative.

FIG. 3A. G6PDH (wild type) amino acid sequence (SEQ ID No. 1); is derived from Leuconostoc pseudomesenteroides Leuconostoc pseudomesenteroides.

FIG. 3B.G6PDH (D306C) amino acid sequence (SEQ ID No. 2).

FIG. 3C.G6PDH (D375C) amino acid sequence (SEQ ID No. 3).

FIG. 3D.G6PDH (G426C) amino acid sequence (SEQ ID No. 4).

Detailed Description

Examples

EXAMPLE 1 Synthesis of phenytoin derivatives

1. Synthesis of Compound 2

Phenytoin (2.00 g,7.94 mmol) and K ₂ CO ₃ (1.65 g,11.90 mmol) was dissolved in DMF (10 mL) and the reaction system was charged with the resulting solutionCompound 1 (1.42 g,6.35 mmol) was reacted for 16h at 50 ℃.

The reaction system was returned to room temperature (20-25 ℃) and water was added to the reaction system, and extraction was performed using ethyl acetate, and the organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and the organic solvent was removed under reduced pressure, and purified by chromatography (EA/pe=1:3) to give compound 2 (2.04 g, 81.6%) as a colorless oil.

2. Synthesis of Compound 3

Compound 2 (2.04 g,5.20 mmol) was dissolved in ethanol (50 mL), naOH (2N, 10 mL) was added to the reaction, and the mixture was stirred at room temperature (20-25 ℃ C.) for 2h. The pH was adjusted to 5 using HCl (1N), the solvent was removed under reduced pressure and purified by column chromatography (MeOH/DCM=1:20) to give compound 3 as a white solid (1.20 g, 60.0%).

3. Synthesis of phenytoin derivatives

Compound 3 (117 mg,0.32 mmol) and compound 4 (56 mg,0.32 mmol) were dissolved in DCM (5 mL), triethylamine (98 mg,0.96 mmol) was added dropwise thereto, HATU (147 mg,0.39 mmol) was added and stirred at room temperature (20-25 ℃ C.) for 5h. Water (30 mL) was added to the reaction system, the mixture was extracted with DCM, and the organic phase was washed with saturated brine and dried Na ₂ SO ₄ Drying, removal of solvent under reduced pressure, preparation of plate purification, to give phenytoin derivative (100 mg, 67%).

The effect of this example is to make phenytoin carry a group that can bind to the enzyme.

EXAMPLE 2 coupling of phenytoin derivatives with G6PDH molecules

The G6 PDH-phenytoin conjugate according to the present application was coupled as follows: the thiol-reactive group (such as, but not limited to, a maleimide group) on the phenytoin derivative molecule is covalently bound to the thiol group on the G6PDH molecule.

1. Preparing a solution:

phenytoin derivative solution: 10mg/ml of the phenytoin derivative prepared in example 1 was dissolved in DMF;

g6pdh solution: g6PDH (mutant of the present application or prior art mutant), PB 100mmol, naCl 100mmol, ph=8.0;

coupling solution: 100mM PB/K, 100mM EDTA, 150mM NaCl, pH=7.2;

desalination solution: 100mM PB/K, 100mM EDTA, 150mM NaCl, pH=7.2.

2. Coupling operation: 4ml of G6PDH solution, 15.2ml of coupling solution and 0.8ml of phenytoin derivative solution were reacted at room temperature (20 to 25 ℃) for 4 hours.

3. After the reaction system is subjected to oscillation reaction for 4 hours at room temperature, eluting by using a desalting column by using the desalting solution, and collecting protein peaks to obtain a product, namely the G6 PDH-phenytoin conjugate.

EXAMPLE 3 preparation of the kit

The following kit for detecting phenytoin was prepared, which comprises:

reagent R1 comprising:

100mM PB buffer, pH 7.2

15mM glucose 6-phosphate

15mM beta-nicotinamide adenine dinucleotide

2.5mg/L phenytoin antibody (commercially available antibody, without particular limitation)

150mM NaCl

1g/L bovine serum albumin

1g/L Tween20

1g/L sodium azide;

reagent R2, comprising:

100mM PB buffer, pH 7.2

0.1mg/L G6 PDH-phenytoin conjugate

1g/L bovine serum albumin

1g/L Tween 20

1g/L sodium azide;

calibration material: 100mM PB buffer, pH 7.2, 0, 2.5, 5.0, 10, 20, 42mg/L phenytoin (or added as needed);

quality control product: 100mM PB buffer, pH 7.2, and 5.0, 15, 25mg/L phenytoin (or added as needed).

Test case

Reaction time: 10min, wherein the incubation time is 4.7min, after adding reagent R2 and incubating for 1min, the read absorbance A1 is measured, after incubating for 1min again, the read absorbance A2 is measured, and Δa= (A2-A1)/min is calculated. Calculating the content of phenytoin in the sample by a calibration curve: phenytoin = sample tube absorbance × calibrator concentration/calibrator absorbance.

The phenytoin assay kit prepared in example 3 was subjected to performance testing, with the main testing properties being total inaccuracy, reproducibility, recovery, linearity, and accelerated stability at 37 ℃.

TABLE 1 full automatic Biochemical instrument parameters

Detection example 1 phenytoin detection kit calibration absorbance

TABLE 2 scaling absorbance for phenytoin assay kits

Note that: the mutant with the code of A45C in the prior art has a mutation site corresponding to the 46 th position of the FIG. 3A.

Detection example 2 total imprecision of phenytoin detection kit

TABLE 3 Total imprecision

Detection example 3 phenytoin detection kit reproducibility

TABLE 4 repeatability

Detection example 4 recovery of phenytoin detection kit

TABLE 5 recovery

Detection example 5 phenytoin detection kit linearity

TABLE 6 linearity

Test example 6.37℃acceleration stability

TABLE 7 accelerated stability at 37℃

The calibrated absorbance drops by about 15% after 7 days of acceleration at 37℃for the reagent of the present application, and by about 95% after 7 days of acceleration at 37℃for the control reagent.

Detection example 7 antibody inhibition Rate

1. Principle of detection of antibody inhibition

When the antibody is combined with the G6 PDH-phenytoin conjugate, the activity of the G6PDH enzyme is influenced due to steric hindrance, so that the efficiency of catalyzing NAD to be converted into NADH is reduced, and the difference between an added antibody and an experimental group without the added antibody is compared by detecting the change of the NADH amount, wherein the difference is expressed as the inhibition capability of the antibody on the G6 PDH.

2. Reaction system

TABLE 8 preparation of reagents for detection of antibody inhibition

TABLE 9 detection of on-machine parameters for antibody inhibition

Detecting machine type	Yaban C16000
		Analysis/time/point	Rate/10 min/28-32 points
R1/S	120:20
		Wavelength (auxiliary/main)	405/340
Reaction type	Incremental increases

3. Results

And comparing the absorbance measurement value of the G6 PDH-phenytoin conjugate when the antibody is added with the antibody is not added with the antibody, and obtaining the inhibition condition of the antibody on the G6 PDH.

Antibody inhibition ratio = [1- (absorbance change value of G6 PDH-phenytoin with antibody/absorbance change value of G6 PDH-phenytoin without antibody) ] ×100%.

Compared with published mutation sites, the mutant has obviously improved antibody inhibition rate, and can reach more than 30% and up to 55%. Whereas the inhibition rate of the mutation sites (e.g.A45C, K C) which have been used before is only about 40% or even lower.

TABLE 10 antibody inhibition by different G6PDH mutants

While not being limited to a particular theory, it may be explained in part as: compared with the G6PDH mutant in the prior art, the mutation site (i.e. the site for introducing free sulfhydryl) in the enzyme mutant (D306C, D375C, G C) is the coupling site with hapten (such as hormone, small molecule drug and the like). When hapten is combined with hapten specific antibody at this position, the steric hindrance formed has the greatest effect on the activity of G6PDH enzyme, and after mutation is introduced, the steric folding of the molecule cannot be substantially influenced. Therefore, the position of this mutation site is very important, and it is necessary to combine the activity of the G6PDH enzyme, the spatial folding of the coupling molecule, and the sufficient exposure of the hapten epitope.

Because the enzyme mutant has obvious improvement on the antibody inhibition rate, after the conjugate of the enzyme mutant and phenytoin is prepared into a kit, the reagent has obvious performance improvement on the performance aspects of repeatability, total inaccuracy, linearity, stability and the like.

Claims

1. A phenytoin assay kit comprising:

-a first reagent comprising a substrate, a phenytoin antibody;

-a second agent comprising a conjugate;

-optionally, a quality control comprising 10mM to 500mM buffer, 0mg/L to 42mg/L phenytoin;

the conjugate is prepared from a glucose 6-phosphate dehydrogenase mutant and a phenytoin derivative according to a molar ratio of 1:1, coupling;

preferably, the phenytoin derivative is represented by formula I below:

the glucose 6-phosphate dehydrogenase mutant comprises the mutation D306C compared to the wild-type glucose 6-phosphate dehydrogenase; the glucose 6-phosphate dehydrogenase mutant is shown in SEQ ID No. 2.

2. The phenytoin assay kit of claim 1, comprising:

a first reagent comprising:

10mM to 500mM, preferably 100mM to 300mM, buffer,

5mM to 25mM, preferably 10mM to 20mM, substrate,

0.1 to 5mg/L, preferably 1 to 2.5mg/L, of phenytoin antibody,

10mM to 300mM, preferably 150mM to 200mM NaCl,

0.1g/L to 5g/L, preferably 1g/L to 5g/L, of a stabilizer,

0.1g/L to 5g/L, preferably 1g/L to 5g/L, of surfactant,

0.1g/L to 5g/L, preferably 1g/L to 5g/L preservative;

a second reagent comprising:

10mM to 500mM, preferably 100mM to 300mM, buffer,

0.1mg/L to 1mg/L of the conjugate,

0.1g/L to 5g/L, preferably 1g/L to 5g/L, of a stabilizer,

0.1g/L to 5g/L, preferably 1g/L to 5g/L, of surfactant,

0.1g/L to 5g/L, preferably 1g/L to 5g/L preservative;

the buffer is selected from one or a combination of the following: tromethamine buffer, phosphate buffer, tris-HCl buffer, citric acid-sodium citrate buffer, barbital buffer, glycine buffer, borate buffer, tris buffer; the pH of the buffer is from 6 to 8, preferably from 7 to 7.5;

the stabilizer is selected from one or a combination of the following: bovine serum albumin, trehalose, glycerol, sucrose, mannitol, glycine, arginine, polyethylene glycol 6000, polyethylene glycol 8000;

the surfactant is selected from one or a combination of the following: brij35, triton X-100, triton X-405, tween20, tween30, tween80, coconut fatty acid diethanolamide, AEO7;

the preservative is selected from one or a combination of the following: azide, MIT, PC biologic preservative, merthiolate;

the azide is selected from: sodium azide, lithium azide

The substrate comprises: glucose-6-phosphate, beta-nicotinamide adenine dinucleotide.

3. The phenytoin assay kit of claim 1, comprising:

a first reagent comprising:

100mM PB buffer, pH 7.2,

15mM glucose 6-phosphate,

15mM beta-nicotinamide adenine dinucleotide,

2.5mg/L phenytoin antibody,

150mM NaCl、

1g/L bovine serum albumin,

1g/L Tween20、

1g/L sodium azide;

a second reagent comprising:

100mM PB buffer, pH 7.2,

0.1mg/L of the conjugate,

1g/L bovine serum albumin,

1g/L Tween20、

1g/L sodium azide;

a calibrator, comprising:

100mM PB buffer, pH 7.2

0mg/L to 42mg/L phenytoin;

a quality control article comprising:

100mM PB buffer, pH 7.2

5.0mg/L to 25mg/L phenytoin.