Pharmacokinetics of methotrexate

Huffman, David H.; Wan, Suk Han; Azarnoff, Daniel L.; Hoogstraten, Barth

doi:10.1002/cpt1973144part1572

Cited by 129 publications

(33 citation statements)

References 7 publications

(8 reference statements)

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“…Quite marked interpatient variation in the rate of distribution after an i.v. dose was evident in this study, and was similar to that reported in adults (Huffman et al, 1973). This may have been due to differences in tissue-or serum protein-binding associated with very high drug concentrations.…”

supporting

confidence: 89%

Serum profiles of methotrexate after its administration in children with acute lymphoblastic leukaemia

Pinkerton¹,

Welshman²,

Bridges³

1982

Br J Cancer

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supporting

confidence: 89%

Serum profiles of methotrexate after its administration in children with acute lymphoblastic leukaemia

Pinkerton¹,

Welshman²,

Bridges³

1982

Br J Cancer

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“…While the utility of routine pharmacokinetic monitoring is apparent, in practice the existing techniques for methotrexate assay have been complex, time consuming, and of limited availability. The other methods include a highly sensitive dihydrofolate reductase inhibition assay (9,11), radioimmunoassay (24), a less sensitive fluorometric method (9), and the use of radiolabeled drug (22,23). The present competitive binding procedure has sensitivity comparable to the enzymatic method, and is capable of determining levels below 5 X 10-9 M, the probable threshold for toxicity to normal tissue (25).…”

mentioning

confidence: 99%

Competitive protein binding assay for methotrexate.

Myers¹,

Lippman²,

Elliot³

et al. 1975

Proc. Natl. Acad. Sci. U.S.A.

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(1) and osteogenic sarcoma (2). Both systemic and intrathecal regimens have been hampered by the occasional development of serious toxicities, such as neurologic sequelae (3), renal failure (4), and myelosuppression. While the etiology of these complications is not well understood, they appear in some cases to be associated with delayed elimination of drug from cerebrospinal fluid (5) or the systemic circulation (6), and pharmacokinetic monitoring may be helpful in their prevention and management (6).Heretofore, routine monitoring of methotrexate pharmacokinetics has not been possible in most institutions due to the complexity of existing assay methods. In the present report, we describe the development of a highly specific, rapid, and sensitive assay based on the high affinity binding of methotrexate to dihydrofolate reductase. In addition to its advantages for routine clinical use, the assay has broad potential application to antifolate research in that it utilizes techniques which allow direct measurement of the association constant of antifolates and dihydrofolate reductase under optimum binding conditions. MATERIALS AND METHODSPartially purified dihydrofolate reductase from dichloromethotrexate-resistant Lactobacillus casei (New England Enzyme Center, Boston, Mass.) was used throughout this study. This enzyme preparation formed 4.6 Aumol of tetrahydrofolate/min per mg protein at pH 7.5 and 370 and was able to bind 1.9 nmol of methotrexate per mg of protein at pH 6.2 and 23'.Unlabeled methotrexate (0.15 M potassium phosphate buffer, pH 6.2, and 23°) (Drug Research and Development Branch, National Cancer Institute) and 4-amino-4-deoxy-10-methylpteroic acid (a gift of Dr. David Johns, National Cancer Institute) were purified by chromatography on DEAE-cellulose with a HC03-elution gradient as previously described (7,8). [3',5',9(n)-3H]methotrexate, 9.5 Ci/ mmol (Amersham-Searle) was diluted in 0.1 M potassium phosphate, pH 8.0, to a final concentration of 2 mCi/ml, and stored at -70°. This methotrexate preparation proved unstable and decomposed, forming radioactive decomposition products which were not adsorbable by charcoal, thus increasing the background. For this reason, the labeled methotrexate was also repurified by chromatography on DEAE-cellulose as described above whenever the background exceeded 150 cpm.Plasma samples containing 100 units of heparin per ml were obtained from patients receiving high dose methotrexate infusion and cerebrospinal fluid was obtained from patients receiving intrathecal methotrexate. All samples were stored at -20°. Prior to analysis samples were acidified to Immediately following addition of the enzyme-NADPH solution, the tubes were mixed by Vortex agitation and 25 Al of a charcoal slurry was added (Norit A, 10 g/100 ml; bovine serum albumin, Fraction V, 2.5 g/100 ml; and high-molecular-weight dextran, 0.1 g/100 ml, all from Sigma Chemical Co.) and pH was adjusted to 6.2 with 1 N HCL. Samples were again mixed by Vortex agitation and centrifuged at 700 X g for 30 min. A 200 ...

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“…In man, 4-amino-N10-methyl pteroic acid is found in the urine 24-96 h after the administration of MTX, in amounts up to 30%o of the total dose MTX given. It is, however, not detectable at all during the first 24 h (Huffman et al, 1973). Because of the cross-reactivity of 4-amino-N10-methyl pteroic acid in the MTX RIA of urine, samples collected more than 24 h after a single dose of MTX, or at any time during long-term MTX treatment, will give falsely high results for urinary MTX excretion.…”

Section: Antiserum Productionmentioning

confidence: 99%

“…The great improvement in antitumour therapy achieved with it in recent years has resulted not only from increased clinical experience, but also from a knowledge of the pharmacokinetics of the drug (Henderson et al, 1965a;Henderson, Adamson and Oliverio, 1965b;Huffman et al, 1973;Bischoff et al, 1971;Dedrick, Bischoff and Zaharteo, 1970). The value of measuring the concentration of MTX in various body fluids during treatment has recently been shown by a number of workers (Bleyer, Chabner, and Ommaya, 1973;Freeman-Narrod et al, 1975;Frei et al, 1975;Shapiro, Young and Mehla, 1975).…”

mentioning

confidence: 99%

Development and application of a radioimmunoassay for methotrexate

Aherne¹,

Piall²,

Marks³

1977

Br J Cancer

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Summary.-An antiserum to methotrexate has been produced in a sheep against a conjugate of ovalbumin and methotrexate (MTX) prepared using a water-soluble carbodiimide. The antibodies produced were specific for substances containing the 2,4-diamino pteridine structure. Naturally occurring folates did not interfere with the assay. A radioimmunoassay has been developed using this antiserum, which can be used to measure MTX concentrations of less than 1 ng/ml in biological samples without prior extraction. The concentrations of MTX in the blood and urine of patients following a single i.v. bolus injection and following oral administration of the drug have been measured. The published radioimmunoassays for MTX have been compared.

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Pharmacokinetics of methotrexate

Cited by 129 publications

References 7 publications

Serum profiles of methotrexate after its administration in children with acute lymphoblastic leukaemia

Serum profiles of methotrexate after its administration in children with acute lymphoblastic leukaemia

Competitive protein binding assay for methotrexate.

Development and application of a radioimmunoassay for methotrexate

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