Serum concentrations of Methotrexate (MTX) were evalated in oral cancer patients treated with combination therapy of MTX·5-FU. The dose of MTX (1-2.5mg/kg) was determined according to the functional condition of the kidney. Blood samples were taken immediately after the administration of MTX and at 6, 24, and 48 hours after the administration. MTX in serum was then measured by Fluorescence Polorization Immunoassay.
The results obtained were as follows :
1.Serum concentration of MTX reached teh effective concentration for therapy (1×10^-5M) immediately after the administration.
2. At 24 hours after the administration, serum concentration of MTX dropped below the concentration (1×10^-5M) that was reported to cause critical side effects.
3. The administration of calcium leucovorin was effective in preventing side effects such as stomatitis.
4. This combination therapy could also be applicable to the patients with slight kidney dysfunction.
These results suggest that monitoring the change of MTX concentration in serum is useful for making a treatment plan of MTX·5-FU therapy and for preventing critical side effects.