Interactions of some commonly used drugs with human α-thrombin.

Adverse side effects of drugs are often caused by the interaction of drug molecules to targets other than the intended ones. In this study, we investigated the off-target interactions of some commercially available drugs with human α-thrombin. The drugs used in the study were selected from Super Drug Database based on the structural similarity to a known thrombin inhibitor argatroban. Interactions of these drugs with thrombin were initially checked by in silico docking studies and then confirmed by thrombin inhibition assay using a fluorescence microplate-based method. Results show that the three commonly used drugs piperacillin (anti-bacterial), azlocillin (anti-bacterial), and metolazone (anti-hypertensive and diuretic) have thrombin inhibitory activity almost similar to that of argatroban. The Ki values of piperacillin, azlocillin, and metolazone with thrombin are .55, .95, and .62 nM, respectively. The IC50 values of piperacillin, azlocillin, and metolazone with thrombin are 1.7, 2.9, and 1.92 nM, respectively. This thrombin inhibitory activity might be a reason for the observed side effects of these drugs related to blood coagulation and other thrombin activities. Furthermore, these compounds (drugs) may be used as anti-coagulants as such or with structural modifications.

Invalidity for Pseudomonas aeruginosa of an accepted model of bacterial permeability to beta-lactam antibiotics.

The accepted model for the penetration of beta-lactam antibiotics into gram-negative bacteria is that proposed by Zimmermann and Rosselet (Antimicrob. Agents Chemother. 12:368-372, 1977). The model assumes (i) that diffusion of the antibiotic molecules across the outer membrane obeys Fick's law and can be characterized by a permeability constant for any given combination of organism and drug, (ii) that drug hydrolysis within the periplasm obeys Michaelis-Menten kinetics, and (iii) that a steady state is rapidly attained between drug uptake and hydrolysis. The model has allowed accurate prediction of antibiotic MICs for Escherichia coli strains from a knowledge of their beta-lactamase production and permeability characteristics. It has been suggested that the model is inappropriate for Pseudomonas aeruginosa, but attempts to confirm this have been bedevilled by experimental difficulties in estimating permeability coefficients for this species. In the present study, we tested a prediction of the model that the overall resistance of P. aeruginosa transconjugants containing a plasmid-encoded beta-lactamase should continue to depend partly on permeability. Transconjugants with PSE-4 beta-lactamase were constructed in host strains with widely different levels of intrinsic, presumably impermeability-determined resistance. Contrary to the prediction of the model, all the transconjugants developed identical overall levels of resistance to substrate beta-lactams, such as azlocillin and cefoperazone, irrespective of the initial levels of intrinsic resistance of the recipient strains. We conclude that the model is inappropriate for P. aeruginosa, and possible explanations for the organism's behavior are discussed.

Azlocillin and mezlocillin concentration in human prostatic tissue.

The concentrations of azlocillin and mezlocillin in human prostatic tissue obtained by transurethral resection or enucleation were measured after two 2.0-gram doses of either drug. The average plasma concentration of azlocillin and mezlocillin at time of tissue sampling was 64.9 and 36.3 micrograms/ml, respectively, and tissue concentration at the time of sampling was 22.9 micrograms/g for azlocillin and 9.4 micrograms/g for mezlocillin. The plasma/tissue concentration ratio for mezlocillin was 0.25 and for azlocillin 0.35. Concentrations of mezlocillin in tissue obtained by transurethral resection were similar to those obtained by enucleation. Azlocillin and mezlocillin in appropriate doses achieve a concentration in human prostatic tissue above the inhibitory concentration for common bacterial pathogens.

[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.

Beta-lactamase lability and inducer power of newer beta-lactam antibiotics in relation to their activity against beta-lactamase-inducibility mutants of Pseudomonas aeruginosa.

The interactions of imipenem, carbenicillin, cefotaxime, ceftriaxone, and azlocillin with the chromosomal beta-lactamase of Pseudomonas aeruginosa were compared. Imipenem was hydrolyzed very slowly (kcat, 1/min) and induced beta-lactamase synthesis strongly. Its minimal inhibitory concentrations (MICs) reflected this behavior, being equal (1-2 micrograms/ml) for enzyme-inducible strains and their stably derepressed mutants. Mutants that had basal (i.e., minimal and uninducible) enzyme production were eight- to 16-fold more susceptible to imipenem than were inducible or stably derepressed strains. Carbenicillin was stable to hydrolysis (kcat, less than 0.1/min) and induced weakly at low concentrations. Consequently its MICs were equal for beta-lactamase-inducible strains and for their basal mutants. Stable beta-lactamase derepression generally did not increase resistance to carbenicillin significantly. Azlocillin, cefotaxime, and ceftriaxone were labile to hydrolysis (kcat, 12-297/min) but induced poorly. Consequently their MICs for enzyme-inducible strains equaled those for basal mutants but were elevated for derepressed mutants.

[In vitro model for the study of the concentration kinetics of antibiotic combinations and their antibacterial activity]. / In vitro-Modell zur Untersuchung der Konzentrationsverläufe von Antibiotikakombinationen und deren antibakterieller Aktivität.

The concentration kinetics of combinations of antibiotics similar to those taking place after i.v. administration was simulated in an in vitro model taking into account the different half-life periods of the antibiotics. A hose pump was used for continuous supply of sterile nutrient to a liquid bacterial culture containing both antibiotics in a preselected concentration and for removal of fluid from the system at an identical flow rate. To account for the different half-life periods of the antibiotics, a solution containing the antibiotic having a longer half-life in a corresponding concentration was continuously added by pumping. Samples were taken at fixed intervals to determine bacterial counts and check the expected concentrations of active substance did not contain antibiotics. This model has been developed to enable a determination of the dynamic relationship between the course of concentrations of antibiotics and their antibacterial activity. To permit a statement on the synergistic, indifferent or antagonistic activity of the combination, in analogy to the FIC indices in the checkerboard technique, the relative reduction of the bacterial count by the combination as compared to the individual components at time t was calculated. The model has been demonstrated by the example of the combined action of azlocillin and gentamicin against a strain of Klebsiella pneumoniae. In a simple way, the model permits any increase in the number of combination partners having different half-life periods. The mathematical development of the model is explained in detail.

Bactericidal activity of ciprofloxacin alone and in combination with azlocillin in an in-vitro capillary model.

An in-vitro pharmacokinetic model was used to study the bactericidal activity of ciprofloxacin, alone and in combination with azlocillin. Ciprofloxacin alone produced excellent bactericidal activity against highly susceptible strains of Escherichia coli and Klebsiella pneumoniae. Against a strain of Pseudomonas aeruginosa, ciprofloxacin in clinically achievable dosing schedules produced a rapid bactericidal effect, but bacterial regrowth occurred. Azlocillin in combination with ciprofloxacin produced a rapid bacterial kill and regrowth was prevented. Further consideration of the clinical role of this combination is warranted.

Comparative pharmacokinetics of azlocillin and piperacillin in normal adults.

The single-dose pharmacokinetics of azlocillin and piperacillin were compared by using a randomized, crossover design. The concentrations of azlocillin in serum were consistently higher than those of piperacillin throughout an 8-h study. The area under the time-concentration curve of azlocillin was significantly greater than that of piperacillin, and the total body clearance of azlocillin was significantly lower than that of piperacillin.

Pharmacokinetics of azlocillin after intramuscular application.

The first pharmacokinetic data are reported of azlocillin injected intramuscularly to adult probands. The blood serum and urinary levels of azlocillin were determined microbiologically in 8 healthy volunteers after intramuscular injection of 2 grams. Peak serum levels of azlocillin were found by the end of hour 1 after injection, average level was (55.06 +/- 10.25) mg/l. At hour 2 the average level was (33.64 +/- 6.46) mg/l. and at hour 4, (9.47 +/- 1.79) mg/l. The biological half-life was 1.4 hour. In urine, (41.2 +/- 7.7)% of the administered dose was eliminated within 8 hours on average.

Susceptibility of Pseudomonas aeruginosa to beta-lactam antibiotics.

Since the discovery of carbenicillin in 1970, several groups of beta-lactam agents with remarkable activity against P. aeruginosa are actually available among penicillins such as ticarcillin, azlocillin, piperacillin, apalcillin and among cephalosporins: cefoperazone, cefsulodin as well as new structures including monobactams (aztreonam) and carbapenems with imipenem. An attempt to establish hierarchy in terms of weight for weight activity, particularly against susceptible isolates is made. The most active antimicrobial agents are: imipenem, apalcillin, ceftazidime, cefsulodin, piperacillin and azlocillin. The bactericidal activity is reported for virtually all of them but more accurate techniques such as time-killing curves are needed to make comparisons, because some discrepancies were reported. Nevertheless, among several factors affecting their inhibitory and bactericidal activities, some of them appeared predominant: inoculum effect and beta-lactamases. The different behavior of beta-lactam antibiotics may be in relation with other mechanisms such as impermeability. A few surveys on the resistance mechanism indicated that impermeability can be prevalent, instead beta-lactamases. But in any case, the enzyme distribution showed carbenicillinases (PSE-1, PSE-4) and OXA were observed with a high prevalence among ticarcillin-resistant isolates and more recently cephalosporinases. These drugs acted synergistically with all of the aminoglycosides in vitro against P. aeruginosa isolates and also in animal models of infection. If the synergism appeared to play a major role in the therapy of P. aeruginosa infections, these new beta-lactam antibiotics offer the possibility of other approaches to combination therapy.

Comparison of the antibacterial activity of azlocillin and ticarcillin in vitro and in irradiated neutropenic mice.

The antibacterial efficacy of azlocillin against Pseudomonas aeruginosa was quantitatively assessed in short-term growth curves in vitro and in a short-term thigh muscle infection in granulocytopenic mice. Ticarcillin was used as the reference drug. The antibacterial effect in vitro was expressed as the difference between the logarithms of the numbers of cfu in the presence and absence of antibiotics (log ratio). The log ratio-time curves could be described by a concentration-dependent parameter, i.e., the inhibition constant (i). According to a standard parallel line bio-assay, based on values of i, azlocillin was 3.80 times more active than ticarcillin (coefficient of variation 27%). Tobramycin in a concentration of 0.19 mg/l, which is not effective in itself, potentiated both drugs by a factor of 3.85 (coefficient of variation 26%). In the in vivo model ticarcillin showed a dose-dependent antibacterial effect, whereas the effect of azlocillin was limited and not dose dependent. The effect of tobramycin in a dose of 4 mg/kg was additive for both penicillins. The results obtained in vivo were less favourable for azlocillin than would be predicted on the basis of the in-vitro results.

Pharmacokinetics of high-dose azlocillin sodium in patients with cystic fibrosis.

The pharmacokinetics of high-dose azlocillin sodium was studied in 18 patients with cystic fibrosis. Nine male and nine female patients with a mean age of 14.7 years (range 3 to 29 years) participated in the study. They received azlocillin 450 mg/kg/day (as the sodium salt) in six divided doses. During a steady-state dosing interval, a dose of azlocillin was coadministered with a 10-mg/kg dose of iothalamate sodium as a 30-minute infusion. Serum concentrations of azlocillin and iothalamate were determined by high-pressure liquid chromatography assay. The data were analyzed using model-independent methods. The mean elimination rate constant for azlocillin was 0.64 +/- 0.22 hr-1 and the mean serum half-life was 1.22 +/- 0.39 hr. Total clearance of azlocillin, calculated by noncompartmental analysis, was 77.2 +/- 26.4 mL/min/sq m. Glomerular filtration rate, as estimated by measuring iothalamate clearance, was 79.6 +/- 21.9 mL/min/sq m. The total clearance of azlocillin correlated with iothalamate clearance. Patients with cystic fibrosis appear to eliminate azlocillin more rapidly than healthy individuals. This rapid elimination warrants the use of high doses to maintain high serum concentrations.

Clinical pharmacology of extended-spectrum penicillins in infants and children.

Compared with previously available penicillins, piperacillin, azlocillin, and mezlocillin have increased activity in vitro against gram-negative bacilli. After intravenous administration of conventional doses (50 to 100 mg/kg) in children, peak concentrations of these drugs are approximately 70 to 350 micrograms/ml. For piperacillin, azlocillin, and mezlocillin, the half-lives during the beta elimination phase (t 1/2 beta) are approximately 0.5 to 0.75, 0.8 to 1.7, and 0.8 to 1.0 hours, respectively. In patients receiving the higher dosage, particularly of azlocillin, the t 1/2 beta may be prolonged by approximately 20%. A total daily dosage of 300 mg/kg or 9 gm/m2 given in four to six divided dosages should produce peak concentrations of approximately 150 micrograms/ml, and concentrations greater than 16 micrograms/ml for at least 2 hours after each administration. Lower daily dosages are needed in neonates, but precise dosage recommendations cannot be made at this time. Only approximately 60% of piperacillin and approximately 45% of azlocillin are eliminated unchanged in the urine; thus only modest dosage reductions are needed in patients with decreased renal function. In children, adverse effects have been infrequent.

Azlocillin levels in human tears and aqueous humor.

We administered 4 g of azlocillin sodium intravenously to 24 patients scheduled to undergo elective intraocular surgery and collected specimens of serum, tears, and aqueous humor from zero to six hours after infusion for assay by high-pressure liquid chromatography. We found that azlocillin is distributed into tears and penetrates into the aqueous humor of human volunteers with noninflamed eyes after a single intravenous dose. Levels of 4.17 micrograms/ml and 4.44 micrograms/ml were achieved in tears and aqueous humor, respectively.

Pharmacokinetic studies of azlocillin and piperacillin during late pregnancy.

In this paper pharmacokinetic data of acylureidopenicillins (azlocillin and piperacillin) in pregnant women in the last trimenon are compared with those from nonpregnant controls. Four g of each drug was administered as slow bolus injection intravenously. The concentrations in serum and urine of both drugs were determined by polarographic and microbiological methods, for comparison. We used for evaluation of pharmacokinetic data a computer program based on the equations of a two-compartment open pharmacokinetic model. Our investigations show that there are not any different pharmacokinetic values of both antibiotics between pregnant women and healthy nonpregnant volunteers. We can state that both antibiotics are well determined by both analyzing methods which give us identical pharmacokinetic results.

[The effect of infusion rate on pharmacokinetic parameters of azlocillin and mezlocillin]. / Uber die Bedeutung der Applikationsgeschwindigkeit für die pharmakokinetischen Parameter von Azlocillin und Mezlocillin.

Azlocillin (Securopen) and mezlocillin (Baypen) were given to 3 healthy subjects as intravenous infusion. The dose of 4 g was administered to each person within 5, 15, and 30 min in a randomized crossover design. Using HPLC the unchanged penicillin antibiotics were determined quantitatively, their metabolites were assessed qualitatively. The same specimens were also studied by means of a bioassay (agar diffusion technique). Both methods yielded similar serum and urine concentrations besides the urinary excretion of azlocillin. Here the bioassay measured higher amounts indicating an antibacterially active metabolite being excreted in the urine. No dependence upon infusion time was found. Since both drugs were tested with the same dosis in the same subjects, their pharmacokinetic parameters could be compared: mezlocillin, being more lipophilic than azlocillin, showed a higher volume of distribution and therefore lower serum concentrations. Renal clearance was the same for both drugs, but mezlocillin was excreted to a smaller extent in the urine. Higher total clearance and shorter elimination half-life of mezlocillin indicate a greater extrarenal elimination. The results suggest fast application of both penicillins. There is no pharmacokinetic reason for a prolongation of infusion times.

Serum and sputum concentrations of azlocillin, cefoperazone and ceftazidime in patients with cystic fibrosis.

Single-dose pharmacokinetics of azlocillin, cefoperazone and ceftazidime were studied in 17 patients with cystic fibrosis (CF). All patients had broncho-pulmonary infections caused by Pseudomonas aeruginosa. Three groups of five, six, and six patients were treated with azlocillin, cefoperazone, or ceftazidime, respectively. The size of the single dose was 133 mg/kg for azlocillin, 66.7 mg/kg for ceftazidime and 66.7 mg/kg for cefoperazone. The clearance values for the three antibiotics calculated from the single-dose data were, on the average, higher than the values previously reported for normal subjects. After the first dose, the patients received a repeated-dose treatment with the same antibiotic. During the first 5 days of therapy, a complement postural drainage of sputum was obtained four times a day for each patient. Cefoperazone could be measured in 47 (39.2%) of the 120 sputum samples assayed while ceftazidime was shown to be present in all 120 sputum samples examined. Azlocillin was not detected in any of the 100 sputum samples assayed.

Azlocillin and cefonicid penetration into bone enhanced by probenecid.

Azlocillin (AZL) and cefonicid (CFD) penetration into rabbit humerus and scapula was evaluated with and without concomitantly administered probenecid. Groups of animals received either 70 mg of AZL intravenously or 20 mg of CFD intramuscularly per kg of body weight; other groups were pretreated with 40 mg of probenecid per kg before the administration of antibiotics. Peak levels of AZL in the sera of animals not receiving probenecid were 76.0 micrograms/ml at 30 min and declined to 7.7 micrograms/ml by 2.0 h. Maximum concentrations in bone were 2.7 micrograms/g in the humerus and 7.1 micrograms/g in the scapula at 1 h. Pretreatment with probenecid significantly elevated levels of AZL in both serum and bone while increasing the half-life in serum from 0.44 to 0.65 h. Maximum drug concentrations in bones of probenecid-pretreated animals were 3.9 and 11.7 micrograms/g in the humerus and scapula, respectively, with detectable levels persisting in bone for up to 4 h. The peak level of CFD alone in serum was 36.7 micrograms/ml at 30 min and declined to 0.86 micrograms/ml at 8 h. Maximum concentrations in bone were 0.66 micrograms/g in the humerus at 1 h and 1.8 micrograms/g in the scapula at 2 h. Pretreatment with probenecid significantly elevated levels of CFD in both serum and bone while increasing the half-life in serum from 1.4 to 2.94 h. Pretreatment with probenecid achieved maximum concentrations of 1.7 and 2.8 micrograms/g in the humerus and scapula, respectively. Detectable levels of CFD persisted in the humerus for up to 4 h and in the scapula for 8 h.

Pseudomonas aeruginosa beta-lactamase as a defence against azlocillin, mezlocillin and piperacillin.

Azlocillin, mezlocillin and piperacillin are weak substrates for the chromosomal beta-lactamase of Pseudomonas aeruginosa, and hydrolysis kinetics were calculated. Enzyme function in the living cell was studied by comparing antibiotic activity against a typical Ps. aeruginosa strain with inducible beta-lactamase expression with antibiotic activity against beta-lactamase uninducible and constitutive mutants. The inducible organism was less sensitive than its uninducible mutant to all three agents; this difference was more apparent at high inocula than low and in broth than in agar. These differences involved both enzyme induction and selection of genotypically enzyme derepressed variants. The penicillins were not, however, efficient beta-lactamase inducers at low concentrations and their activity against the inducible organism was antagonized by more potent inducers. Secondary inducers did not antagonize antibiotic activity against beta-lactamase uninducible and constitutive organisms. The beta-lactamase constitutive mutants were highly resistant to the three antibiotics tested.