In-vitro-Kombinationswirkung von Carbenicillin, Mezlocillin und Azlocillin mit Gentamicin und Sisomicin auf Pseudomonas aeruginosa, Serratia marcescens, Klebsiella pneumoniae und indol-positive Proteus-Stämme

[N-formimidoyl-thienamycin: in vitro activity in bacteria with resistance to beta-lactam antibiotics or gentamicin]

The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of N-formimidoyl-thienamycin were determined for 25 strains each of Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens and Pseudomonas aeruginosa which were resistant to gentamicin and/or acylureido penicillins or cefotaxime, cefoperazone or moxalactam, and for 38 strains of the group D streptococci. The drug was very active against the most frequently encountered gram-negative resistant causative organisms of nosocomial infections. The MIC ranged from 0.25-1 mg/l for multiresistant Enterobacteriaceae, and from 0.5-4 mg/l for multiresistant P. aeruginosa. The group D streptococci (enterococci) showed a low MIC (median: 0.75 mg/l); the median of the MBC was greater than 64 mg/l, however.

Combined action of decreasing concentrations of azlocillin and sisomicin on Pseudomonas aeruginosa as assessed in a dynamic in vitro model

The effect of decreasing concentrations of azlocillin and sisomicin on Pseudomonas aeruginosa was examined. Logarithmically growing bacterial cultures were incubated in an ultrafiltration cell, and after adding the antibiotics, the culture medium was diluted every 20 min without any decrease in cell density. The turn-over of medium resulted in the elimination of azlocillin with a half-life of 75 min. This simulated serum kinetics in vivo. When testing sisomicin, small amounts of this agent were added during every dilution step to achieve a half-life of 120 min. Growth conditions were comparable in all experiments. The simultaneous combination of azlocillin and sisomicin resulted in strong synergism as assessed by higher killing rates and more prolonged growth inhibition of surviving bacteria. Comparable results were observed when both drugs were added at intervals of 40 min. When applied at intervals of 120 min, the combined effect of azlocillin and sisomicin was reduced, but still superior to the effect of double the concentration of each compound alone. Thus, neither pre-treatment with azlocillin nor with sisomicin impaired the antibacterial activity of the combination partner. This seems to be of clinical importance since the agents may be administered at different times during combined therapy.

[Azlocillin--a new anti-pseudomonas penicillin. A review of the literature and pharmacokinetic studies]

We studied the pharmacokinetics of azlocillin in 11 healthy persons following an i. v. infusion of 5 g over 30 minutes. The azlocillin concentrations in serum and urine were measured microbiologically. The serum concentrations averaged 530.5 (+/- 79.2) mg/l at the end of the infusion and 9.4 (+/- 4.3) mg/l six hours later. 73.8% of the dose was excreted in the urine during a period of six hours. The serum concentrations of azlocillin were analysed using a two-compartment model, and the pharmacokinetic constants were calculated by a computer. The average biological half-life (beta-phase) of azlocillin was 70.2 (+/- 7.8) min, the plasma clearance was 1.869 (+/- 0.284) ml/sec and the distribution volume (Vd area) was 11.34 (+/- 2.05) l, i. e. 0.17 l/kg.

Comparative study of the binding of acylureidopenicillins and carbenicillin to human serum proteins

The binding of the acylureidopenicillins azlocillin and mezlocillin to serum proteins was investigated by means of equilibrium dialysis and ultracentrifugation. The penicillin concentrations were determined by the agar diffusion test and by circular dichroism. The degree of binding is dependent on the penicillin concentration. At a mean penicillin concentration of 20 microgram/ml 39% of azlocillin is bound by serum proteins and 35% of mezlocillin. The acylureidopenicillins are bound to about the same degree by the two proteins albumin and gamma globulin, which occur in different concentrations in serum. The binding affinity delta F degree for the interaction between azlocillin and mezlocillin to human albumin is equal to -15,389 J/mol. The corresponding values for the binding of ampicillin and carbenicillin are -17,340 and -16,800 J/mol. Albumin has one binding site of a high affinity and two binding sites of a low affinity for the acylureidopenicillins. Measurements of partition coefficients of the penicillins for isobutanol and aqueous solution show that the interaction between acylureidopenicillins and serum is mainly hydrophobic in nature. This can be deduced from the fact that for example in the presence of sisomicin azlocillin is not displaced from its albumin binding site, in contrast to carbenicillin. The reason for this difference in behaviour lies in the fact that carbenicillin, like sisomicin, is bound to the serum proteins mainly by ionic bonds. In the case of azlocillin, however, hydrophobic bounds predominate which are not influenced by the ionic bonds of sisomicin.

Comparative antibacterial activity of azlocillin, mezlocillin, carbenicillin and ticarcillin and relative stability to beta-lactamases of pseudomonas aeruginosa and klebsiella aerogenes

The antibacterial activities of two ureidopenicillins, azlocillin and mezlocillin, were compared with those of the alpha-carboxypenicillins, carbenicillin and ticarcillin, against a large number of gram-positive and gram-negative bacteria. All four penicillins were active against a wide range of bacteria including Pseudomonas aeruginosa, but there were differences in the antibacterial spectra and in the antibacterial effects demonstrated by the two classes of penicillins. In particular, the minimum inhibitory concentrations of azlocillin and mezlocillin against Klebsiella aerogenes and against P. aeruginosa were greatly influenced by the size of bacterial inoculum tested whereas there was no significant inoculum effect with carbenicillin and ticarcillin. In stability tests, the ureidopenicillins were inactivated rapidly by the beta-lactamases of K. aerogenes and P. aeruginosa whereas the alpha-carboxypenicillins were stable. It seems probable that the inoculum effect seen with azlocillin and mezlocillin in antibacterial tests with K. aerogenes and P. aeruginosa is associated with the instability of the compounds to the beta-lactamases of these bacteria.

[Current chemotherapy of infections caused by Pseudomonas aeruginosa (author's transl)]

In addition to carbenicillin, the newer beta-lactam antibiotics such as ticarcillin and azlocillin are now available for the chemotherapy of Pseudomonas aeruginosa infections. We investigated the in vitro effect of these antibiotics on 233 isolates from clinical material. We were particularly careful, when choosing the experimental material, to exclude copies of the same individual strain, and we achieved this by combining various epidemiological typing procedures. A comparison of carbenicillin, ticarcillin and azlocillin according to the concentrations at which half of the 233 strains were inhibited showed the ticarcillin values to be higher than those of azlocillin by a factor of 2.1, and carbenicillin values to be higher than those of azlocillin by a factor of 4.9. Individual strains also occurred in which the inhibitory concentration for azlocillin was higher than that of carbenicillin (5 strains) or ticarcillin (11 strains). In 17 out of the 233 isolates no therapeutic success would have been within reach even with the newer beta-lactam antibiotics. The use of ticarcillin and azlocillin permits an extension of the indications for therapy with beta-lactam antibiotics in P. aeruginosa infections, from hitherto 76%, to 90% of the cases. If one includes the aminoglycosides gentamycin, tobramycin, sisomycin and amikacin in the therapeutic armoury, then the proportion of in vitro sensitive strains of P. aeruginosa in the material submitted for examination rises to 98%.