Independent measurement of ampicillin and cloxacillin in mixtures.

L. D. Sabath, V. J. Estey, M. Finland

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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.
Original languageUndefined/Unknown
Pages (from-to)468-470
Number of pages3
JournalApplied Microbiology
Issue number3
StatePublished - 1967


  • Ampicillin/an [Analysis]
  • Biological Assay
  • Cloxacillin/an [Analysis]
  • Methicillin/an [Analysis]
  • Penicillin G/an [Analysis]
  • Penicillinase/me [Metabolism]
  • Sarcina/me [Metabolism]
  • Staphylococcus/me [Metabolism]

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