(tye'' roe thrye' sin).
» Tyrothricin is an antibacterial substance produced by the growth of Bacillus brevis Dubos (Fam. Bacteriaceae). It consists principally of gramicidin and tyrocidine, the tyrocidine usually being present as the hydrochloride. It contains not less than 900 µg and not more than 1400 µg of tyrothricin per mg.
Packaging and storage Preserve in tight containers.
USP Reference standards 11
USP Gramicidin RS
Identification Add about 5 mg to 5 mL of p-dimethylaminobenzaldehyde TS, and shake for 2 minutes. Add 2 drops of sodium nitrite solution (1 in 150) and 5 mL of water, and mix: a blue color is produced.
Loss on drying 731 Dry about 100 mg, accurately weighed, in a capillary-stoppered bottle in vacuum at a pressure not exceeding 5 mm of mercury at 60 for 3 hours: it loses not more than 5.0% of its weight.
Assay Proceed as directed for gramicidin under AntibioticsMicrobial Assays 81, using a suitable, accurately weighed portion of Tyrothricin dissolved quantitatively in alcohol to yield a stock solution of convenient concentration. Dilute an accurately measured volume of this solution quantitatively and stepwise with alcohol to obtain a Test Dilution having a concentration of tyrothricin assumed to be 5.0 times the median dose level of the gramicidin Standard. Multiply the result of the gramicidin assay by 5.0 to obtain the amount of tyrothricin, in µg, in each mL of the Test Dilution.
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USP35NF30 Page 4977