A: The retention time exhibited by theophylline in the chromatogram of the Assay preparationcorresponds to that of theophylline in the chromatogram of the Standard preparation,as obtained in the Assay.

B: Transfer a quantity of finely ground Tablets,equivalent to about 100mg of oxtriphylline,to a suitable test tube,and proceed as directed in Identificationtest Bunder Oxtriphylline Delayed-release Tablets,beginning with “add 10mLof methanol.”

Test 1 (for products labeled as 400-mg tablets):If the product complies with this test,the labeling indicates that it meets USPDrug Release Test 1.Proceed as directed for Method Bunder Delayed-release Articles—General Drug Release Standard,except to use Acceptance Table 1under Extended-release Articles—General Drug Release Standard.

pH7.5buffer— Transfer 27.22g of monobasic potassium phosphate to a 4-liter volumetric flask,add 1liter of water and 816mLof 0.2Nsodium hydroxide,and dilute with water to about 3800mL.Adjust with 0.2Nsodium hydroxide or phosphoric acid to a pHof 7.5,and dilute with water to volume.

Medium: 0.1Nhydrochloric acid for the first hour,then pH7.5buffer;900mL.

Apparatus 2: 50rpm.

Procedure— Determine the amount of C12H21N5O3dissolved from UVabsorbances at the wavelength of maximum absorbance at about 248nm of filtered portions of the solution under test,diluted with Dissolution Mediumif necessary,in comparison with a Standard solution having a known concentration of USP Oxtriphylline RSin the same medium.

Timesand Tolerances—

Test 2 (for products labeled as 600-mg tablets):If the product complies with this test,the labeling indicates that it meets USPDrug Release Test 1.Proceed as directed for Method Bunder Delayed-release Articles—General Drug Release Standard,except to use Acceptance Table 1under Extended-release Articles—General Drug Release Standard.

pH7.5buffer ,Medium,Apparatus,and Procedure—Proceed as directed for Test 1.

Timesand Tolerances—