Medium: 0.1Nhydrochloric acid;900mL.

Apparatus 2: 50rpm.

Time: 45minutes.

Procedure— Determine the amount of C8H11N5O3dissolved from UVabsorption at the wavelength of maximum absorbance at about 254nm on filtered portions of the solution under test,suitably diluted with 0.1Nhydrochloric acid in comparison with a Standard solution having a known concentration of USP Acyclovir RSin the same Medium.

Tolerances— Not less than 80%(Q)of the labeled amount of C8H11N5O3is dissolved in 45minutes.

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

Test preparation— Use the Assay preparation.

Procedure— Inject a volume (about 20µL)of the Test preparationinto 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 riis the peak response for each impurity;and rsis 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.

Change to read:

Mobile phase— Prepare a filtered and degassed solution of 0.02Macetic acid.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

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

System suitability preparation 2— Dissolve an accurately weighed quantity of guanine in 0.1Nsodium hydroxide,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 2.0µg per mL.USP28

Standard preparation— Dissolve an accurately weighed quantityUSP28of USP Acyclovir RSUSP28in 0.1Nsodium hydroxide,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentrationUSP28of about 0.1mg per mL.USP28

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

Chromatographic system (see Chromatography á621ñ)— 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 1.5mLper minute.Chromatograph System suitability preparation 1,USP28and record the peak responses for acyclovirUSP28as directed for Procedure:the relative retention times are about 0.6for guanine and 1.0for 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 peakUSP28is 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%.USP28

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto 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 Cis the concentration,in mg per mL,of USP Acyclovir RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.