» Methotrexate Tablets contain not less than 90.0 percent and not more than 110.0 percent of the labeled amount of methotrexate (C20H22N8O5).
Packaging and storage Preserve in well-closed containers. A unit-of-use container contains a quantity of Tablets sufficient to provide one week's therapy as indicated in the labeling.
Labeling When packaged in a unit-of-use container, the label indicates the total amount of methotrexate present as one week's supply.
USP Reference standards 11
Identification Dissolve 1 Tablet in 100 mL of dilute hydrochloric acid (1 in 100), and filter the solution: the UV absorption spectrum of the filtrate exhibits maxima and minima at the same wavelengths as that of a solution containing about 2.5 mg of USP Methotrexate RS in 100 mL of dilute hydrochloric acid (1 in 100).
Medium: 0.1 N hydrochloric acid; 900 mL.
Apparatus 2: 50 rpm.
Time: 45 minutes.
Procedure Determine the amount of C20H22N8O5 dissolved from UV absorbances at the wavelength of maximum absorbance at about 306 nm of filtered portions of the solution under test, suitably diluted with Dissolution Medium, in comparison with a Standard solution having a known concentration of USP Methotrexate RS in the same Medium.
Tolerances Not less than 75% (Q) of the labeled amount of C20H22N8O5 is dissolved in 45 minutes.
Uniformity of dosage units 905: meet the requirements.
pH 6.0 Buffer solution , Mobile phase, System suitability solution, System suitability test, and Standard preparationProceed as directed in the Assay under Methotrexate.
Assay preparation Weigh and finely powder not less than 20 Tablets. Weigh accurately a portion of the powder, equivalent to about 25 mg of methotrexate, and transfer to a 250-mL volumetric flask. Add about 200 mL of Mobile phase, and dissolve the methotrexate using a mechanical shaker or ultrasonic bath. Dilute with Mobile phase to volume, and mix.
Procedure Proceed as directed for Procedure in the Assay under Methotrexate. Calculate the quantity, in mg, of methotrexate (C20H22N8O5) in the portion of Tablets taken by the formula:
250C(PU / PS)in which C is the concentration, in mg per mL, of USP Methotrexate RS in the Standard preparation; and PU and PS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.
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USP35NF30 Page 3858