Methotrexate Assay

Accurately screen for MTX with low-end sensitivity.

The ARK Methotrexate Assay is the only liquid methotrexate assay on the market. It provides a broad assay range of 0.04–1.20 µmol/L for accurate measurements of Methotrexate. The measurements obtained are used in monitoring levels of methotrexate to help ensure appropriate therapy. Methotrexate is an antimetabolite used in the treatment of specific cancers, psoriasis, rheumatoid arthritis, and other autoimmune conditions.

  • Proven homogeneous enzyme immunoassay similar to EMIT® technology
  • Applications available for ADVIA® Chemistry Systems, Dimension® and Dimension Vista® Integrated Systems, and Viva™ Drug Testing Systems
  • Convenient, liquid-stable, ready-to-use reagents
  • 10X more sensitive than Syva Emit assay—can provide physicians with results when needed, especially at 72-hour mark post-dose, when levels are expected to be <0.05
  • Very low cross-reactivity to 7-hydroxymethotrexate (<0.07%)
Fale Conosco

Características e Benefícios

The ARK Methotrexate assay is the only liquid methotrexate assay on the market. It provides an assay range of 0.04–1.20 µmol/L that meets customers’ needs for low-end sensitivity.

  • Methotrexate is an antineoplastic drug that is used in the treatment of specific cancers (especially pediatric), psoriasis, rheumatoid arthritis, and other autoimmune conditions.
  • Methotrexate is extremely potent and has the potential to be very toxic. It inhibits a key enzyme and affects DNA/RNA synthesis in the cells. Thus, it prevents the growth of cells that grow rapidly, such as cancer, bone marrow, and skin cells.
  • Methotrexate serum levels are dependent on many variables, including dose, mode of administration, individual metabolism, and individual pharmacokinetics. Leucovorin is usually administered intravenously as a rescue (counteracting) therapy.

Guidelines for methotrexate therapy with leucovorin rescue usually recommend continuance of leucovorin until the methotrexate level falls below 0.05 μmol/L, although ≤0.10 μmol/L is sometimes followed. This is why low-level sensitivity is so important, especially for pediatric patients.

Especificações Técnicas

Precision
Precision was determined as described in CLSI/NCCLS Protocol EP5-A2. The six-level ARK Methotrexate Control and pooled human specimens containing methotrexate were used in the study. Each level was assayed in quadruplicate twice a day for 20 days. Each of the runs per day was separated by at least two hours. The within run, between day, total SD, and percent CVs were calculated.

 

 

 

Within Run

Between Day

Total

Sample

N

Mean (µg/mL)

SD

CV (%)

SD

CV (%)

SD

CV (%)

ARK Methotrexate Control

LOW

160

0.06

0.005

8.2

0.005

7.3

0.007

10.7

MID

160

0.37

0.011

3.0

0.008

2.1

0.014

3.8

HIGH

160

0.76

0.032

4.3

0.030

4.0

0.045

5.9

5*

160

4.8

0.15

3.1

0.13

2.8

0.20

4.2

50*

160

49

1.36

2.8

2.32

4.8

2.72

5.6

500*

160

476

15.17

3.2

30.75

6.5

34.66

7.3

Patient Pool

LOW

160

0.07

0.006

9.1

0.005

7.5

0.008

11.7

MID

160

0.41

0.013

3.3

0.026

6.4

0.029

7.2

HIGH

160

0.82

0.037

4.5

0.043

5.2

0.057

7.0

5*

160

4.6

0.14

3.1

0.183

4.0

0.24

5.3

50*

160

45

1.33

3.0

2.63

5.9

2.93

6.6

500*

160

461

11.84

2.6

27.04

5.9

29.60

6.4

Specificity
Cross-reactivity to 7-Hydroxymethotrexate, the major metabolite
The ARK Methotrexate Assay did not crossreact with the major metabolite 7-OH-MTX.

Reagent Lot

7-OH MTX (µmol/L)

Serum Control (µmol/L)

MTX (µmol/L)

Cross Reactivity (%)

Cross Reactivity 7-OH MTX in the presence of 0.05 µmol/L MTX

D2

5.0

0.06

0.06

0.01

D3

5.0

0.04

0.05

0.02

Cross Reactivity 7-OH MTX in the presence of 0.05 µmol/L MTX

D2

50.0

0.44

0.47

0.07

D3

50.0

0.46

0.48

0.05

Cross-reactivity to the minor, inactive metabolite 2,4-diam ino-N10-methylpteroic acid (DAMPA)
The ARK Methotrexate Assay crossreacts substantially with the minor metabolite DAMPA. Tests were performed in the absence of the parent drug methotrexate. Crossreactivity to DAMPA ranged 64.3 to 100%. The assay should not be used during possible compassionate therapy with glucarpidase (carboxypeptidase G2) that rapidly converts circulating methotrexate to DAMPA.

Drugs that crossreact
The ARK Methotrexate Assay crossreacts slightly with triamterene and trimethoprim, however these drugs may be contraindicated for MTX cancer treatment due to additional adverse effects if co-administered. The structures of these compounds closely match the pteridine ring moiety of methotrexate.

Compound

Tested (µmol/L)

Apparent MTX (µmol/L)

Cross Reactivity (%)

MTX Absent

Triamterene

25

0.46

1.85

Trimethoprim

100

0.17

0.17

MTX Present 0.05 (µmol/L)

Triamterene

25

0.89

3.32

Trimethoprim

100

0.16

0.12

MTX Present 0.05 (µmol/L)

Triamterene

25

1.04

2.31

Trimethoprim

100

0.99

0.54

Cross-reactivity to folate analogs and other compounds
The ARK Methotrexate Assay did not cross-react (≤ 0.01%) with folate analogs or other compounds at ≥ 1000 μmol/L as tested.

Compound

Texted (μmol/L)

Adriamycin

1000

Cyclophosphamide

1500

Cytosine

1000

Dihydrofolic Acid

1000

DL-6-Methyl-5,6,7,8-Tetrahydropterine

1000

Folic Acid

1000

Folinic Acid (leucovorin)

1000

5-Fluorouracil

3000

6-Mercaptopurine

1000

5-Methyltetrahydrofolic acid

1000

Prednisolone

1000

Pyrimethamine

1000

Sulfamethoxazole

1600

Tetrahydrofolic Acid

1000

Vinblastine

1000

Vincristine

1000