Medium: 0.1 N hydrochloric acid; 900 mL.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C8H11N5O3 dissolved from UV absorption at the wavelength of maximum absorbance at about 254 nm on filtered portions of the solution under test, suitably diluted with 0.1 N hydrochloric acid in comparison with a Standard solution having a known concentration of USP Acyclovir RS in the same Medium.

Tolerances— Not less than 80% (Q) of the labeled amount of C8H11N5O3 is dissolved in 45 minutes.

Mobile phase, Standard preparation, and Chromatographic system— Proceed as directed in the Assay.

Test preparation— Use the Assay preparation.

Procedure— Inject a volume (about 20 µL) of the Test preparation into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the percentage of each impurity in the portion of Tablets taken by the formula: in which ri is the peak response for each impurity; and rs is the sum of the responses for all of the peaks: not more than 2.0% of guanine is found; and not more than 0.5% of any other impurity is found.

(Official January 1, 2007)

Mobile phase— Prepare a filtered and degassed solution of 0.02 M acetic acid. Make adjustments if necessary (see System Suitability under Chromatography 621).

System suitability preparation 1— Dissolve accurately weighed quantities of USP Acyclovir RS and guanine in 0.1 N sodium hydroxide, and dilute quantitatively, and stepwise if necessary, with water to obtain a solution having a known concentration of about 0.1 mg of each per mL.

System suitability preparation 2— Dissolve an accurately weighed quantity of guanine in 0.1 N sodium hydroxide, and dilute quantitatively, and stepwise if necessary, with water to obtain a solution having a known concentration of about 2.0 µg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Acyclovir RS in 0.1 N sodium hydroxide, and dilute quantitatively, and stepwise if necessary, with water to obtain a solution having a known concentration of about 0.1 mg per mL.

Assay preparation— Weigh and finely powder not fewer than 10 Tablets. Transfer an accurately weighed quantity of powder, equivalent to about 10 mg of acyclovir, to a 100-mL volumetric flask, dissolve in 10 mL of 0.1 N sodium hydroxide, dilute with water to volume, mix, and filter.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The column temperature is maintained at 40. The flow rate is about 1.5 mL per minute. Chromatograph System suitability preparation 1, and record the peak responses for acyclovir as directed for Procedure: the relative retention times are about 0.6 for guanine and 1.0 for acyclovir; the resolution, R, between guanine and acyclovir is not less than 2.0; and the relative standard deviation for replicate injections for the acyclovir peak is not more than 2.0%. Chromatograph System suitability preparation 2, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the peak responses. Calculate the quantity, in mg, of acyclovir (C8H11N5O3) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Acyclovir RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.