Independent measurement of ampicillin and cloxacillin in mixtures.
A simplified method of assaying mixtures of ampicillin and cloxacillin is presented. The method consists of cylinder-plate assays of appropriately diluted samples in three assay systems in which: (i) cloxacillin is measured, utilizing agar seeded with a penicillinase-producing Staphylococcus aureus; (ii) ampicillin is measured after the greatest dilution practicable, by use of agar seeded with Sarcina lutea; and (iii) the proportion of activity found in the second assay that remains after treatment with staphylococcal penicillinase is determined on agar seeded with S. lutea. The error was 4% or less when each system was run in quadruplicate, except when there was 10 or more times as much cloxacillin as ampicillin, in which case the greatest error was 12%. Mixtures of methicillin with benzylpenicillin or with ampicillin can also be quantitated by this method.
D000667:Ampicillin / Q000032:analysis*; D001681:Biological Assay; D003023:Cloxacillin / Q000032:analysis*; D008712:Methicillin / Q000032:analysis; D010400:Penicillin G / Q000032:analysis; D010405:Penicillinase / Q000378:metabolism; D012505:Sarcina / Q000378:metabolism; D013210:Staphylococcus / Q000378:metabolism
D000667:Ampicillin; D010405:Penicillinase; D003023:Cloxacillin; D010400:Penicillin G; D008712:Methicillin