Amoxycillin and Ampicillin

In vitro antibacterial activities of ampicillin and amoxycillin were compared against pigmented and non-pigmented strains of Serratia marcescens. Ampicillin appeared more effective than amoxycillin; three-fourths of all strains consistently exhibited an ampicillin minimum inhibitory concentration (MIC) of at least one tube less than that recorded for amoxycillin. Complete cross resistance was not observed as has previously been inferred. Further, greater bactericidal activity was demonstrated with ampicillin; minimum bactericidal concentrations (MBC) were either the same as or one tube greater than the MIC. MBCs for amoxycillin, however, were significantly higher; often four to five times greater than the MIC. Ampicillin exhibited greater bactericidal activity as inferred from differences observed in the biological lesions induced, as recorded through observations by scanning electron microscopy (SEM). Spheroplasts were the predominant morphological alteration induced by ampicillin. In contrast, only filament formation, which demonstrated a degree of reversibility, was induced by amoxycillin.     

Reduction in Incidence of Ampicillin Rash by Purification of Ampicillin

Purification of ampicillin (Penbritin) with respect to protein impurities has been found significantly to reduce the incidence of rashes in treated patients. This may be related to findings in animals that injections of the isolated protein impurity can induce the formation of circulating IgG antibodies and skin-sensitizing antibodies.     

Prospective Study of Ampicillin Rash

A multicentre prospective study of 933 patients being treated with ampicillin showed a rash incidence of 7·3%. The rash was commonest in women and patients suffering from viral infections. Most rashes were maculopapular and were not associated with features of true penicillin allergy. We conclude that the development of a maculopapular rash during or after treatment with ampicillin is not in itself a contraindication to future treatment with the penicillins.     

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.     

Ampicillin serves as an electron donor

1. The effect of ampicillin on cytochrome c reduction and on the superoxide production of human neutrophils stimulated by phorbol myristate acetate (PMA) was investigated. 2. Ampicillin did not stimulate the superoxide production of intact (resting) neutrophils and not amplify the superoxide production of neutrophils stimulated by phorbol myristate acetate (PMA). 3. However, ampicillin dose-dependently increased the reduction of cytochrome c. 4. In addition, 50 mM ampicillin stimulated a superoxide dismutase-inhibitable reduction of cytochrome c by 0.70 +/- 0.02 (mean +/- SD) nmol/min and a superoxide dismutase-noninhibitable reduction of cytochrome c by 2.08 +/- 0.03 (mean +/- SD) nmol/min. 5. These results suggest that ampicillin serves as an electron donor and/or a superoxide generator.