Methotrexate AssayAccurately 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%)   
  • Features & Benefits

    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.

    Technical Specifications

    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

    1