A rapid and specific radioimmunoassay for methotrexate

Area of Science:

• Pharmacology
• Analytical Chemistry
• Biochemistry

Background:

• Accurate quantification of methotrexate is crucial for optimizing patient treatment and minimizing toxicity.
• Existing methods may lack the sensitivity or practicality required for routine clinical monitoring.

Purpose of the Study:

• To develop and validate a sensitive and precise radioimmunoassay (RIA) for methotrexate.
• To assess the utility of the RIA in pharmacokinetic studies and clinical monitoring.

Main Methods:

• Development of a RIA using rabbit-induced antibodies, tritium-labeled methotrexate, and nitrocellulose membrane separation.
• Characterization of antibody specificity by competitive displacement assays.
• Validation against an established enzymic assay for serum samples.

Main Results:

• The developed RIA demonstrated high sensitivity, measuring as little as 0.1 to 1 pmole of methotrexate.
• Assays of serum, cerebrospinal fluid, and urine samples were rapid and easy to perform.
• RIA results correlated well with enzymic assay measurements in pharmacokinetic studies.
• Naturally occurring folates did not interfere with the assay.

Conclusions:

• The developed radioimmunoassay provides a sensitive, precise, and practical method for monitoring methotrexate levels.
• This RIA is suitable for pharmacokinetic studies and therapeutic drug monitoring in various biological matrices.
• The assay's specificity and lack of interference from folates enhance its clinical applicability.