Medium: water; 900 mL.

Apparatus 2: 75 rpm, the distance between the blade and the inside bottom of the flask being maintained at 4.5 ± 0.5 cm during the test.

Time: 90 minutes.

Procedure— Determine the amount of C22H24N2O8 dissolved from UV absorbances at the wavelength of maximum absorbance at about 276 nm of filtered portions of the solution under test, suitably diluted with Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Doxycycline Hyclate RS in the same medium.

Tolerances— Not less than 85% (Q) of the labeled amount of C22H24N2O8 is dissolved in 90 minutes.

(Official January 1, 2007)

Mobile phase, Diluent, Resolution solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Doxycycline Hyclate.

Assay preparation— Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of doxycycline, to a 100-mL volumetric flask, add about 75 mL of Diluent, sonicate for 5 minutes, shake for 15 minutes, dilute with Diluent to volume, and mix. Filter through a membrane filter of 0.5 µm or finer porosity.

Procedure— Proceed as directed for Procedure in the Assay under Doxycycline Hyclate. Calculate the quantity, in mg, of doxycycline (C22H24N2O8) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Doxycycline Hyclate RS in the Standard preparation, P is the designated potency, in µg of doxycycline per mg, of USP Doxycycline Hyclate RS, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.