An in vitro and pharmacological comparison of amoxicillin and ampicillin.
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Biomedical subjects
Publications and source records attributed to L Weinstein.
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Eighteen strains of Pseudomonas maltophilia and eight strains of P. cepacia were tested for susceptibility to sulfamethoxazole, trimethoprim, and colistin in different combinations. A synergistic effect was found against most of the strains.
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Marked differences were noted among 14 antibiotics in their filterability through collodion (nitrated cellulose) membranes. The findings could not be attributed to differences in molecular weight or degree of serum protein binding, although the latter factor imposed an additional restraint on the passage of certain agents. Poorly filtered antibiotics appeared to be absorbed by the collodion. Some of these observations might be accounted for by the known ability of nitrated cellulose to interact with anions. However, the extreme differences in filterability among the various penicillins and the very restricted passage of certain cationic antibiotics appeared to be better explained by intrinsic differences in the diffusibility of these agents through water. Although differential filtration offers a means of assaying samples containing certain mixtures of antibiotics, the degree of separation exhibited by collodion membranes is not sufficient to make them useful for clinical purposes.
The in vitro bactericidal activity of cefazolin was found to be similar to that of cephaloridine and cephalothin but slightly greater than that of cephalexin against a majority of 233 strains of gram-positive and gram-negative organisms. Cefazolin, however, was two- to eightfold more active than the other two drugs against Escherichia coli and klebsiella. The mean peak concentrations in the serum in 10 normal subjects 1 h after intramuscular injections of 1,000, 500, and 250 mg of cefazolin were 38.8, 18.6, and 12.2 mug/ml, respectively. The antibiotic could still be detected at 8 h. Peak values for a given dose of cephaloridine were comparable. However, blood levels of cefazolin were regularly higher than those of cephaloridine over the first 8 h. The mean half-life of cefazolin in the serum was 2 h, whereas that of cephaloridine was 1.4 h. The degree of serum protein-binding was strikingly higher for cefazolin (81%) than for cephaloridine (24%), suggesting that the antibacterial activity of the former in serum might be less than that of cephaloridine after equal doses. This proved to be the case when the bacterial activity of blood drawn 1, 4, and 8 h after injection of the two drugs was examined.
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