Assay preparation 1 (where it is represented as being in a single-dose container)—Constitute Colistimethate for Injection in a volume of water,accurately measured,corresponding to the volume of diluent specified in the labeling.Withdraw all of the withdrawable contents,using a suitable hypodermic needle and syringe,and quantitatively dilute with Buffer No.6to obtain a solution having a convenient concentration.

Assay preparation 2 (where the label states the quantity of colistin equivalent in a given volume of constituted solution)—Constitute Colistimethate for Injection in a volume of water,accurately measured,corresponding to the volume of diluent specified in the labeling.Quantitatively dilute an accurately measured volume of the constituted solution with Buffer No.6to obtain a solution having a convenient concentration.

Procedure— Proceed as directed for Colistimethate Sodium under Antibiotics—Microbial Assays á81ñ,using an accurately measured volume of Assay preparationdiluted quantitatively with Buffer No.6to yield a Test Dilutionhaving a concentration assumed to be equal to the median dose level of the Standard.