Human oral drugs absorption is correlated to their in vitro uptake by brush border membrane vesicles.

Brush border membrane vesicles (BBMV) were prepared from the rabbit small intestine for testing drug absorption potency through the enterocyte's apical membrane, which is an important compartment for drug oral absorption. Some modifications have been made to the traditional vesicle assay for adapting it to the 96-well plate format. The accumulation of 23 reference drugs was measured, and the data showed a good correlation with human oral absorption with a correlation coefficient R=0.853 (P<0.001), with the exception of a few false positive results. As the measured drug absorption may contain a membrane/protein binding component as well as drug uptake into vesicles, these two fractions can be discriminated by changing extravesicular osmolarity using different mannitol concentrations. This model can be applied for evaluating drug absorption rate/mechanisms, and helping drug selection in early drug research and development.

Role of efflux pump(s) in intrinsic resistance of Pseudomonas aeruginosa: active efflux as a contributing factor to beta-lactam resistance.

Wild-type strains of Pseudomonas aeruginosa are more resistant to various beta-lactam antibiotics as well as other agents than most enteric bacteria. Although resistance to compounds of earlier generations is explained by the synergism between the outer membrane barrier and the inducible beta-lactamase, it was puzzling to see significant levels of resistance to compounds that do not act as inducers or are not hydrolyzed rapidly by the chromosomally encoded enzyme. This intrinsic-resistance phenotype becomes enhanced in those strains with the so-called intrinsic carbenicillin resistance. In the accompanying paper (X.-Z. Li, D. M. Livermore, and H. Nikaido, Antimicrob. Agents Chemother. 38:1732-1741, 1994), we showed that active efflux played a role in the resistance, to various non-beta-lactam agents, of P. aeruginosa strains in general and that the efflux was enhanced in intrinsically carbenicillin-resistant strains. We show in this paper that, in comparison with the drug-hypersusceptible mutant K799/61, less benzylpenicillin was accumulated in wild-type strains of P. aeruginosa and that the accumulation levels were even lower in intrinsically carbenicillin-resistant strains. Deenergization by the addition of a proton conductor increased the accumulation level to that expected for equilibration across the cytoplasmic membrane. In intrinsically carbenicillin-resistant isolates, there was no evidence that either nonspecific or specific permeation rates of beta-lactams across the outer membrane were lowered in comparison with those of the more susceptible isolates. Furthermore, these carbenicillin-resistant isolates were previously shown to have no alteration in the level or the inducibility of beta-lactamase and in the affinity of penicillin-binding proteins. These data together suggest the involvement of an active efflux mechanism also in the resistance to beta-lactams. Hydrophilic beta-lactams with more than one charged group did not cross the cytoplasmic membrane readily. Yet one such compound, ceftriaxone, appeared to be extruded from the cells of more-resistant strains, although with this compound effects of proton conductors could not be shown. We postulate that wild-type strains of P. aeruginosa pump out such hydrophilic beta-lactams either from the periplasm or from the outer leaflet of the lipid bilayer of the cytoplasmic membrane, in a manner analogous to that hypothesized for multidrug resistance protein of human cancer cells (M.M. Gottesman and I. Pastan, Annu. Rev. Biochem. 62:385-427, 1993).

Combination therapy with ciprofloxacin plus azlocillin against Pseudomonas aeruginosa: effect of simultaneous versus staggered administration in an in vitro model of infection.

The effect of dose scheduling on the pharmacodynamics of simulated human doses of ciprofloxacin (200 mg intravenously [iv] every 12 h) and azlocillin (4 g iv every 12 h) alone or in combination against Pseudomonas aeruginosa was studied in a two-compartment in vitro kinetic model of infection. Studies with the two drugs in combination were compared using simultaneous or staggered (first doses of each drug were administered 6 h apart) dosing schedules. Bacterial regrowth and resistance were prevented by all combination dosing schedules; however, the simultaneous regimen consistently provided the greatest extent of killing for all strains, particularly in those initially resistant to ciprofloxacin. These enhanced effects of the combination were corroborated by an increase in the peak and duration of bactericidal activity in the analogous "serum" compartment of the model. These data show the potential usefulness of simultaneous dosing of an antipseudomonal beta-lactam with ciprofloxacin against P. aeruginosa.

[The effect of continuous arteriovenous hemofiltration on the pharmacokinetics of azlocillin in anuric patients]. / Der Einfluss der kontinuierlichen arteriovenösen Hämofiltration auf die Pharmakokinetik von Azlocillin bei anurischen Patienten.

The influence of continuous arteriovenous hemofiltration on the pharmacokinetics of azlocillin was examined in eight anuric intensive care patients, each of whom received a short infusion of 5.0 g azlocillin. Azlocillin concentrations in blood were measured simultaneously in the afferent and efferent loops of the amicon Dia 20 hemofilter and in the ultrafiltrate by means of an agar diffusion technique. Pharmacokinetic parameters were calculated by a computer program based on a two compartment model. We found that the elimination half-life of azlocillin ranged between 218.8 and 342.8 min, a result comparable to those of other investigators, who found similar elimination half-lives in anuric patients. During an observation period of 270 min, only 0.2-1.1% of the total dose of azlocillin was eliminated by way of the hemofilter. Apparently, continuous arteriovenous hemofiltration has no clinically relevant implications for the dosage or the dosage intervals of this antibiotic. On the other hand, azlocillin was taken up by the amicon Dia 20 hemofilter during the infusion. After the infusion was stopped the filter released azlocillin to blood and ultrafiltrate. The ratio of concentration in ultrafiltrate to plasma concentration in the afferent loop of the hemofilter was higher for about 45 min during the elimination phase than during the infusion. The volume of distribution was much larger (mean 28.5 l) than that found by other investigators. Therefore, the amicon-Dia 20 hemofilter seems to function as an additional distribution space.(ABSTRACT TRUNCATED AT 250 WORDS)

Atividade de 3 ureidopenicilinas sobre bacilos gram negativos isolados no Recife / Activity of 3 ureidopenicillins on gram negative bacillus isolated in Recife

O estudo comparativo da atividade da azlocilina, da mezlocilina e da piperacilina sobre 123 cepas de bactérias Gram-negativas isoladas nos hospitais do Recife foi efetuado mediante a determinaçäo das CIM e das CBM pela microtécnica de diluiçäo em caldo. Estas três ureidopenicilinas apresentaram uma boa atividade contra E. coli, Salmonella, Shigella, Proteus indol positivo e Klebsiella. Todas as cepas de Pseudomonas foram sensíveis à Azlocilina e à Piperacilina

Comparative efficacy of ciprofloxacin, azlocillin, imipenem/cilastatin and tobramycin in a model of experimental septicemia due to Pseudomonas aeruginosa in neutropenic mice.

The in vivo activity of ciprofloxacin against Pseudomonas aeruginosa was studied in a septicemia model in neutropenic mice and compared to that of other antibiotics with established activity against P. aeruginosa. When given as a single agent, ciprofloxacin proved to be as effective as imipenem/cilastatin, whereas azlocillin and tobramycin were rather ineffective. After infection with higher challenge inocula, combinations of two (synergistic) antibiotics were more effective than single agent therapy in most instances. The combination of ciprofloxacin with azlocillin was at least as effective as that of imipenem/cilastatin with tobramycin. Selection of mutants with decreased sensitivity to ciprofloxacin occurred during therapy, however, post-therapy MICs of ciprofloxacin did not exceed a level of 1 mg/l and rises of MICs did not detrimentally influence treatment outcome. Taken together with the results of earlier studies, our data encourage the use of ciprofloxacin in gram-negative septicemia in neutropenic patients.

[Pharmacokinetics of azlocillin in critical conditions: an individualized schedule of drug administration in relation to anatomo-physiologic and pathologic factors]. / Farmakokinetika azlotsillina pri kriticheskikh sostoianiiakh: individualizatsiia skhemy vvedeniia preparata s uchetom anatomo- fiziologicheskikh i patologicheskikh faktorov.

Azlocillin pharmacokinetics was studied after a single intravenous injection of the antibiotic in a dose of 4 g in 20 patients in critical state. To elucidate the causes of significant individual variability of the antibiotic pharmacokinetics observed in the patients, multiple correlation analysis of the main pharmacokinetic parameters i. e. the area under the concentration/time curve, total clearance, steady-state volume of distribution and mean residence time was performed in regard to the "patient factors" such as sex, age, the volumes of transfused liquid, blood, plasma and blood substitutes, hemoglobin levels, erythrocyte count and ESR. Adequate correspondence of the predicted by the "patient factor" values of the areas under the concentration/time curve and the total clearance to the actually determined values was observed. Correspondence of the predicted values to the steady-state volume of distribution and the mean residence time to the actually determined values was satisfactory. A procedure for design of azlocillin individual dosage regimens based on calculating individual clearance by the "patient factors" is described.

[Azlocillin in the treatment of pulmonary infections in patients with cystic fibrosis: plasma concentrations and therapeutic indications]. / L'azlocillina nel trattamento delle infezioni polmonari dei pazienti affetti da fibrosi cistica: concentrazioni plasmatiche e indicazioni terapeutiche.

Azlocillin plasma concentrations have been studied in 10 cystic fibrosis patients suffering from chronic pulmonary infections with Pseudomonas aeruginosa. Patients were given single i.v. doses of 100 e 200 mg/kg body weight as intravenous infusion over 30 minutes. Azlocillin plasma levels have been assayed by a rapid, sensitive and precise high performance liquid chromatographic method. After the dose of 100 mg/kg body weight concentrations of azlocillin decreased below the therapeutic concentrations after three hours; dose of 200 mg/kg was followed by plasma concentrations in the therapeutically desirable range during the 6-8 hours study period. The pharmacokinetic analysis offers further evidence of the dose-dependent nature of azlocillin elimination. Higher dosage of 200 mg/kg body weight and monitoring of plasma drug levels are recommended in the therapy of patients with cystic fibrosis.

Pharmacokinetic comparison of 5 g of azlocillin every 8 h and 4 g every 6 h in healthy volunteers.

To compare the multiple-dose pharmacokinetics of two dosage regimens of azlocillin, we studied 12 healthy volunteers via a randomized, crossover design with a 2-week washout phase between regimens. Serum and urine samples were collected for 8 h following the fifth dose of a regimen of 4 g every 6 h and the fourth dose of a regimen of 5 g every 8 h. Data for concentrations in serum were fitted to a two-compartment open model by nonlinear regression. Statistically significant differences (P less than 0.05) were observed in the following parameters (mean +/- standard deviation) for the 4- and 5-g regimens, respectively: area under the serum concentration-time curve during the dosing interval, 592 +/- 140 versus 772 +/- 151 micrograms.h/ml; terminal elimination rate constant, 0.5364 +/- 0.0912 versus 0.4758 +/- 0.0486 h-1; renal clearance, 87.6 +/- 16.1 versus 76.1 +/- 13.5 ml/min; maximum drug concentration in serum, 381 +/- 89 versus 473 +/- 90 micrograms/ml; and minimum drug concentration in serum, 19 +/- 10 versus 8 +/- 4 micrograms/ml. No significant differences were seen in the following parameters: V1, V beta, k10, k12, k21, total systemic clearance, and nonrenal clearance. These data support the presence of saturable renal elimination of azlocillin, as well as the feasibility of an 8-h dosing interval.

A comparison of double beta-lactam combinations with netilmicin/ureidopenicillin regimens in the empirical therapy of febrile neutropenic patients.

In a randomized trial ceftazidime plus piperacillin or azlocillin, and netilmicin plus piperacillin or azlocillin were used as initial empirical therapy in 202 febrile neutropenic episodes. Netilmicin plus azlocillin was the most effective combination with a clinical response rate of 81% in clinically and microbiologically documented infections compared with 63% for ceftazidime plus piperacillin. All of the episodes of Gram-negative bacteraemia treated with azlocillin responded compared with 43% of those treated with piperacillin. Gram-positive organisms accounted for 52% of all bacteriologically documented infections and 40% of the febrile episodes were treated with vancomycin for presumptive or documented Gram-positive infection. Patients treated with netilmicin had significantly more nephrotoxicity than those given the double beta-lactam combinations (14.8% vs 3.5%; P less than 0.05). However, this difference was not shown in those patients who did not receive concurrent vancomycin or amphotericin. The double beta-lactam combinations were associated with more hypokalaemia (58.2% vs. 37.7%; P less than 0.05) and more colonization with yeasts (24% vs. 10.4%; P less than 0.05) but there was no evidence that their use was associated with prolongation of neutropenia. These results indicate that ceftazidime plus a ureidopenicillin would be adequate empirical therapy in situations where the concomitant use of nephrotoxic agents precludes the use of aminoglycoside containing combinations.

Concentration of azlocillin in human chondral tissue.

The concentration of azlocillin was determined using high performance liquid chromatography in serum and chondral tissue after intravenous infusion of azlocillin (75 mg/kg body weight). In serum the levels of ten patients (2 to 27 years of age, body weight 12 to 69 kg) decreased from 478 (30 min post infusion) to 120 micrograms/ml (120 min). In contrast, the concentrations in chondral tissue ranged between 24 and 35 mg/g tissue at the corresponding times. Although the mean levels suggest a remarkable penetration of azlocillin into chondral tissue, the high individual differences observed in the tissue levels (2.1 to 138 micrograms/g tissue) require a higher dosage to ensure sufficient antimicrobial therapy in all patients.

[The pharmacokinetics of azlocillin after single and multiple intravenous injections during the third trimester]. / Zur Pharmakokinetik von Azlocillin nach einfacher und wiederholter intravenöser Applikation in der Spätschwangerschaft.

Examining serum level values and urinary concentrations taken from non-pregnant control persons and pregnant women suffering from urinary tract infections (UTI) during the III. trimenon, the pharmacokinetic dates after single and repeated applications of 4 g azlocillin have been evaluated. We used a computer program based on the two-compartment model. It is shown that during pregnancy complicated by UTI the elimination half-life time will be prolonged and returns after therapy nearly to normal values. The results, discussed with the dates given by literature, allow us to state that it is not necessary to change dosage and application interval of azlocillin during pregnancy.

The novel therapeutic implications of azlocillin's dose-dependent pharmacokinetics: contributing physiologic mechanisms and a prospective, cross-over designed trial.

Azlocillin is an important acylureido penicillin antibiotic for the management of complex gram-negative infections particularly those caused by Pseudomonas species. The current studies demonstrate that it manifests dose-dependent pharmacokinetics during the usual regimens of clinical dosing, that enterohepatic recirculation does not occur and that renal tubular secretion (maximum renal tubular secretory capacity 300 +/- 30 micrograms/min) and hepatic metabolism appear to be the dominant contributors to the dose-dependent nature of azlocillin. The possible therapeutic implications of azlocillin's dose dependency were evaluated by undertaking a six-day randomized, prospective, cross-over design study to evaluate the pharmacokinetic disposition of the drug during a 3-g q4h (typically used in adults) regimen versus a 5-g q8h regimen. By using the area under the serum-time concentration curve (AUC) as the major comparative parameter for these two regimens, the results demonstrate that both regimens provide approximately equal quantitative amounts of the drug systemically as a result of azlocillin's dose dependency. The AUC values, although not therapeutic end points, nonetheless correlate well with clinical response to antibiotic therapy. The 5-g q8h regimen was well tolerated. It is less disruptive for patients, requires half the number of intravenous administrations, 17% less drug, and is more cost effective than the 3-g q4h regimen.