Change to read:

Change to read:

Solution A— Prepare a filtered and degassed mixture of 0.17Macetic acid and methanol (125:8).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Solution B: methanol,filtered and degassed.

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed for Chromatographic system.Make adjustments to either solution as necessary (see System Suitabilityunder Chromatography á621ñ).

System suitability solution— Dissolve suitable quantities of purine and USP Acyclovir RSin Solution Ato obtain a solution containing about 0.5µg of each per mL.

Acyclovir standard solution— Dissolve an accurately weighed quantity of USP Acyclovir RSinSolution A,and dilute quantitatively,and stepwise if necessary,withSolution Ato obtain a solution having a known concentration of about 5µg per mL.

Guanine solution— Dissolve about 25mg of guanine,accurately weighed,in 50mLof 0.1Nsodium hydroxide in a 500-mLvolumetric flask,dilute with water to volume,and mix.

Standard solution 1USP28— Transfer 5.0mLofAcyclovir standard solution USP28to a 50-mLvolumetric flask,dilute withSolution Ato volume,and mix.

Standard solution 2— Transfer 5.0mLof Guanine solutionto a 50-mLvolumetric flask,dilute with Solution Ato volume,and mix.USP28

Test solution— Constitute and combine not fewer than 10vials of Acyclovir for Injection.Transfer an accurately measured quantity,equivalent to about 100mg of acyclovir,to a 200-mLvolumetric flask,dilute with Solution Ato volume,and mix.

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 flow rate is about 1mLper minute.The chromatograph is programmed as follows. Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the resolution,R,between purine and acyclovir is not less than 2.0.Chromatograph Standard solution 1and Standard solution 2,USP28and record the peak responses as directed for Procedure:the typicalUSP28retention times for guanine and acyclovir are about 5.8minutes and 14minutes,USP28respectively;and the relative standard deviation of the acyclovir peak area and the guanine peak area for replicate injections is not more than 1%.

Procedure— Separately inject equal volumes (about 50µL)of the Standard solution and the Test solutioninto the chromatograph,record the chromatograms,and measure the peak area responses.Calculate the percentage of guanine in the Acyclovir for Injection by the formula: in whichCis the concentration,in mg per mL,of guanine in theStandard solution;Wis the total weight,in mg,of acyclovir in theTest solutionbased on the label claim;rgis the peak response for guanine,if present,in theTest solution;andrsgis the peak response of guanine in theStandard solution:not more than 1.0%is found.Calculate the percentage of each other impurity in the Acyclovir for Injection by the formula: in which Cis the concentration,in mg per mL,of USP Acyclovir RSin the Standard solution;Wis the total weight,in mg,of acyclovir in the Test solution based on the label claim;riis the peak response for each impurity;and rSis the peak response of acyclovir in the Standard solution:not more than 0.15%for any peak having a relative retention time of about 0.7compared to the acyclovir peak is found;not more than 0.5%of any other individual impurity is found;and the total of all other impurities is not more than 1.0%.

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 0.1Nsodium hydroxide to obtain a solution having known concentrations 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 0.1Nsodium hydroxide to obtain a solution having a known concentration of about 2.0µg per mL.USP28

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

Assay preparation— Constitute,with water,1vial of Acyclovir for Injection.Transfer an accurately weighed amount of this solution,equivalent to about 10mg of acyclovir,to a 100-mLvolumetric flask,and dilute with water to volume.

Chromatographic system (seeChromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.2-mm ×25-cm column that contains packing L1.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 Acyclovir for Injection 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.