Comparative therapeutic efficacy of clinafloxacin in a Pseudomonas aeruginosa mouse renal abscess model

A deep-seated Pseudomonas aeruginosa mouse kidney abscess model was used to compare the therapeutic efficacy of clinafloxacin, a fluoroquinolone in clinical trials, with that of clinically relevant standard drugs. Following 50 mg/kg oral doses, twice daily for five consecutive days, clinafloxacin produced a 4 log decrease in mean bacterial count, the greatest decrease of all drugs tested. The same dosage regimen resulted in complete bacterial eradication in 88% of the kidneys. No other compound produced total bacterial clearance in 50% of the kidneys at the highest dose tested.

Cefepime and amikacin synergy in vitro and in vivo against a ceftazidime-resistant strain of Enterobacter cloacae

The activities of cefepime and amikacin alone or in combination against an isogenic pair of Enterobacter cloacae strains (wild type and stably derepressed, ceftazidime-resistant mutant) were compared using an experimental model of pneumonia in non-leucopenic rats. Animals were infected by administering 8.4 log10 cfu of E. cloacae intratracheally, and therapy was initiated 12 h later. At that time, the animals' lungs showed bilateral pneumonia and contained more than 7 log10 E. cloacae cfu/g tissue. Because rats eliminate amikacin and cefepime much more rapidly than humans, renal impairment was induced in all animals to simulate the pharmacokinetic parameters of humans. In-vitro susceptibilities showed an inoculum effect with cefepime proportional to the bacterial titre against the two strains, but more pronounced with the stably derepressed mutant strain, whereas with bacterial concentrations of up to 7 log10 cfu/mL, no inoculum effect was observed with amikacin. In-vitro killing indicated that antibiotic combinations were synergic only at intermediate concentrations. At peak concentrations, the combination was merely as effective as amikacin alone. At trough concentrations, a non-significant trend towards the superiority of the combination over each antibiotic alone was noted. Moreover, cefepime was either bacteriostatic or permitted regrowth of the organisms in the range of antibiotic concentrations tested. Although each antibiotic alone failed to decrease bacterial counts in the lungs, regardless of the susceptibility of the strain used, the combination of both antibiotics was synergic and induced a significant decrease in the lung bacterial count 24 h after starting therapy when compared with tissue bacterial numbers in untreated animals or animals treated with either antibiotic alone. No resistant clones emerged during treatment with any of the antibiotic regimens studied.

Continuous infusion of ceftazidime with an elastomeric infusion device

The serum disposition, antimicrobial activity, and stability of ceftazidime continuously infused with an elastomeric infusion device (Homepump, Block Medical) were studied. Twelve healthy adult volunteers were given a 500-mg bolus dose of ceftazidime infused i.v. over two minutes, followed by a continuous i.v. infusion of 3 g over 24 hours. Blood samples were drawn five minutes before and at intervals up to 24 hours after the start of the bolus infusion. Samples were collected from the infusers immediately before and at the end of the 24-hour infusion. Infusers were insulated with ice packs. Ceftazidime concentrations were determined by high-performance liquid chromatography. Minimum inhibitory concentrations (MICs), serum inhibitory titers (SITs), and serum bactericidal titers (SBTs) were determined by the microdilution technique. Mean +/- S.D. serum ceftazidime concentrations ranged from 39.50 +/- 6.92 micrograms/ml at peak (30 minutes after the start of the bolus infusion) to 15.30 +/- 2.83 micrograms/mL at trough (24 hours after the start). The ceftazidime MIC for Pseudomonas aeruginosa was 1 microgram/mL; this MIC was exceeded 100% of the time. Serum ceftazidime concentrations achieved a median SIT and SBT of 1:32 and 1:16, respectively, at 30 minutes and 1:8 and 1:8, respectively, at 24 hours. Six infusers met or exceeded the 24-hour infusion time; ceftazidime was stable in these infusers. A 500-mg i.v. bolus of ceftazidime followed by a continuous infusion (3 g over 24 hours) delivered by an elastomeric infusion device produced serum drug concentrations that were constantly above the MIC for P. aeruginosa and maintained serum bactericidal activity against that organism. Adequate stability of ceftazidime was ensured by placing an ice pack next to the infuser.

Intermittent bolus dosing of ceftazidime in critically ill patients

Ceftazidime is frequently used in critically ill patients, particularly for the treatment of Pseudomonas aeruginosa infections. The recommended dosing regimen is based on pharmacokinetic data obtained in healthy volunteers and may not be appropriate in the critically ill. We administered ceftazidime in the maximum recommended dose (2 g i.v. every 8 h) to ten critically ill patients with normal plasma creatinine. Eighteen arterial blood samples were taken from each patient over the first 8 h for measurement of ceftazidime concentrations and subsequent compartmental pharmacokinetic analysis. An additional trough sample was taken from each patient on day 3. Although mean pharmacokinetic variables did not differ from previously reported data in normal volunteers there was wide variability in plasma drug concentrations. Three of our patients had plasma ceftazidime concentrations less than the MIC for P. aeruginosa (8 mg/L) and nine had concentrations less than 5 x MIC, which has been recommended to ensure efficacy. On day 3 trough ceftazidime concentrations were less than the MIC in four out of the seven patients in whom measurements were made and less than 5 x MIC in the remaining three. There was no clinical predictor of which patients would have low plasma concentrations. Our results show that plasma concentrations of ceftazidime are very variable when the recommended intermittent bolus dosing regimen is used and may result in inadequate plasma concentrations of drug in critical infections. This may result in treatment failure and the emergence of antibiotic resistance. A loading dose followed by continuous infusion should overcome these problems but this awaits in-vivo evaluation.

Continuous infusion of ceftazidime in cystic fibrosis patients during home treatment: clinical outcome, microbiology and pharmacokinetics

Acute exacerbations of Pseudomonas aeruginosa lung infections were treated with ceftazidime by continuous infusion in 17 adult patients with cystic fibrosis at home. Ceftazidime was delivered via an infusion pump and the effects of this 3 week home intravenous antibiotic treatment (HIVAT) were prospectively studied over a 2 year period. Patients with cystic fibrosis (eight male and nine female patients; mean age 26.9 +/- 7.6 years, range 15-52 years), received a total of 33 courses of continuous ceftazidime (100 mg/kg/24 h). Clinical data were collected at the start, the end and 4-6 weeks after the end of treatment in 12 patients. Ceftazidime pharmacokinetic data during continuous infusion were obtained from ten patients. The treatment was supervised by the clinician without home visits. All 25 clinically evaluable courses in 12 patients proved efficacious. The mean duration of the courses was 21 days. The entire antibiotic course was administered at home in 88% of the courses. The other 12% was started for 2-3 days as an inpatient. Objective clinical parameters significantly improved. Clinical improvement was noted in 91% of the patients, and lasted at least until 4-6 weeks after the end of the treatment in 70%. The number of cultures positive for P. aeruginosa decreased significantly during antibiotic treatment. Bacterial count returned to pretreatment values 4-6 weeks after treatment. Multiple courses of ceftazidime monotherapy did not result in a lasting increase of ceftazidime-resistant pseudomonas strains. Total body clearance was 9.1 +/- 1.3 L/h. The steady-state ceftazidime serum concentration during continuous infusion was 28.4 +/- 5.0 mg/L. Sputum concentrations were in the range of 0.5-13 mg/L (3.9 +/- 4.0 mg/L). In conclusion, HIVAT with ceftazidime administered by continuous infusion proved clinically effective and did not result in an increase in lasting resistance.

Development and evaluation of a Bayesian pharmacokinetic estimator and optimal, sparse sampling strategies for ceftazidime

Data were gathered during an activity-controlled trial in which seriously ill, elderly patients were randomized to receive intravenous ceftazidime or ciprofloxacin and for which adaptive feedback control of drug concentrations in plasma and activity profiles was prospectively performed. The adaptive feedback control algorithm for ceftazidime used an initial population model, a maximum a posteriori (MAP)-Bayesian pharmacokinetic parameter value estimator, and an optimal, sparse sampling strategy for ceftazidime that had been derived from data in the literature obtained from volunteers. Iterative two-stage population pharmacokinetic analysis was performed to develop an unbiased MAP-Bayesian estimator and updated optimal, sparse sampling strategies. The final median values of the population parameters were follows: the volume of distribution of the central compartment was equal to 0.249 liter/kg, the volume of distribution of the peripheral compartment was equal to 0.173 liter/kg, the distributional clearance between the central and peripheral compartments was equal to 0.2251 liter/h/kg, the slope of the total clearance (CL) versus the creatinine clearance (CLCR) was equal to 0.000736 liter/h/kg of CL/1 ml/min/1.73 m2 of CLCR, and nonrenal clearance was equal to + 0.00527 liter/h/kg. Optimal sampling times were dependent on CLCR; for CLCR of > or = 30 ml/min/1.73 m2, the optimal sampling times were 0.583, 3.0, 7.0, and 16.0 h and, for CLCR of < 30 ml/min/1.73 m2, optimal sampling times were 0.583, 4.15, 11.5, and 24.0 h. The study demonstrates that because pharmacokinetic information from volunteers may often not be reflective of specialty populations such as critically ill elderly individuals, iterative two-stage population pharmacokinetic analysis, MAP-Bayesian parameter estimation, and optimal, sparse sampling strategy can be important tools in characterizing their pharmacokinetics.

Monotherapy with meropenem versus combination therapy with ceftazidime plus amikacin as empiric therapy for fever in granulocytopenic patients with cancer. The International Antimicrobial Therapy Cooperative Group of the European Organization for Research and Treatment of Cancer and the Gruppo Italiano Malattie Ematologiche Maligne dell'Adulto Infection Program

Combinations of beta-lactams plus aminoglycosides have been standard therapy for suspected infections in granulocytopenic cancer patients, especially those with profound long-lasting granulocytopenia. With the advent of new broad-spectrum bactericidal antibiotics such as extended-spectrum cephalosporins or carbapenems, the need to combine beta-lactams with aminoglycosides became more controversial. The objective of this prospective randomized multicenter study was to compare the efficacy, safety, and tolerance of meropenem monotherapy with those of the combination of ceftazidime plus amikacin for the empirical treatment of fever in granulocytopenic cancer patients. Of 1,034 randomized patients, 958 were assessable in the intent-to-treat analysis for response to antibacterial therapy, including 483 in the meropenem group and 475 in the ceftazidime-plus-amikacin group. The median durations of neutropenia were 16 and 17 days, respectively. A successful outcome was reported in 270 of 483 (56%) patients treated with monotherapy compared with 245 of 475 (52%) patients treated with the combination group (P = 0.20). The success rates in the monotherapy group and the combination group were similar by type of infection (single gram-negative bacteremia, single gram-positive bacteremia, clinically documented infection, and possible infection). The occurrence of further infections assessed in patients for whom the allocated regimen was not modified did not differ between the two groups (12% in both groups). Mortality due to the presenting infection or further infection was relatively low (8 patients treated with the monotherapy compared with 13 patients treated with the combination). A total of 1,027 patients were evaluable for adverse events; the proportion of those who developed adverse effects was similar between the two groups (29% in both groups), and only 19 (4%) patients in the monotherapy group and 31 (6%) in the combination group experienced an adverse event related or probably related to the study drug. Allergic reactions were the only reason for stopping the protocol antibiotic(s) (3 and 5 patients, respectively). This study confirms that monotherapy with meropenem is as effective as the combination of ceftazidime plus amikacin for the empiric treatment of fever in persistently granulocytopenic cancer patients, and both regimens were well tolerated.

The pharmacokinetics of ceftazidime in lactating and non-lactating cows

The pharmacokinetics of ceftazidime (CAZ) were studied in lactating (LTG) and non-lactating (NLTG) cows. Two groups (LTG and NLTG) of 5 healthy dairy cows were given ceftazidime (10 mg/ kg body weight) intravenously (i.v.) and intramuscularly (i.m.). Serum and milk (LTG) and serum samples (NLTG) were collected over a 24-h period post-administration. CAZ concentrations in serum and milk were determined by high-performance liquid chromatography, and an interactive and weighted-non-linear least-squares regression analysis was used to perform the pharmacokinetic analysis. The pharmacokinetic profiles in LTG and NLTG cows which had received CAZ i.v. fitted a three-compartment model and a two-compartment model, respectively. The CAZ concentration-time curves in serum and the area under the curve were greater and more sustained (p < 0.05) in the LTG cows by both routes, while the serum clearance (Cls = 72.5 +/- 18.1 ml/h per kg) was lower (p < 0.05) than that in the NLTG cows (Cls = 185.9 +/- 44.2 ml/h per kg). CAZ given i.v. exhibited a relatively long half-life of elimination (t1/2 beta (LTG) = 1.1 +/- 0.2 h; t1/2 beta (NLTG) = 1.4 +/- 0.3 h). Compared with other cephalosporins, CAZ had good penetration into the mammary gland (47.7 +/- 38.2% for CAZ i.v.; 51.1 +/- 39.0% for CAZ i.m.). Finally, the bioavailability of CAZ (F(LTG) = 98.9 +/- 36.8%; F(NLTG) = 77.1 +/- 25.3%) was suitable for its used by the i.m. route in lactating and non-lactating cows.

Serum bactericidal activity of ceftazidime: continuous infusion versus intermittent injections

Since beta-lactam antibiotics have concentration-independent killing, bacterial eradication is a function of the time the serum drug concentration remains above the drug's MIC (T > MIC). We compared the serum bactericidal titers (SBTs) of ceftazidime given by continuous infusion (CI) or by intermittent bolus dosing (BD) against two clinical isolates each of Pseudomonas aeruginosa and Escherichia coli to determine if CI would allow lower daily dosing while still providing equal bactericidal activity compared with BD. This was an open-labeled, randomized, steady-state, four-way crossover study with 12 healthy volunteers. The ceftazidime regimens were 1 g every 8 h (q8h) BD, 1 g q12h BD, 3 g over 24 h CI, and 2 g over 24 h CI. The areas under the bactericidal curves were calculated by the trapezoidal rule using the reciprocal of the SBT. For all organisms the areas under the bactericidal curves for intermittent versus the CI regimens were the same for equal doses (P > 0.05). For both strains of E. coli all four regimens provided SBTs of > or = 1:2 over the dosing interval and 100% T > MIC. The 1-g q8h BD and q12h BD regimens provided T > MIC of 82 and 52%, respectively, for both P. aeruginosa isolates (MICs, 4 micrograms/ml). In comparison, the 2- and 3-g CI regimens always maintained SBTs of > or = 1:2 and T > MIC over the 24-h period as serum drug concentrations were 12.8 +/- 3.0 and 18.2 +/- 4.5 micrograms/ml, respectively. CI optimizes the pharmacodynamic and pharmacoeconomic profile of ceftazidime by providing adequate antibacterial activity over the 24-h dosing period with a reduction in the total daily dose of the antimicrobial agent.

Pharmacokinetic profiles of ceftazidime in cochlear perilymph, cerebrospinal fluid and plasma: a high-performance liquid chromatographic study

A pharmacokinetic profile of the antibiotic ceftazidime was established for perilymph, cerbrospinal fluid (CSF) and plasma in 12 guinea pigs using the technique of high-performance liquid chromatography. The mean peak levels of 13.35 mg/l in perilymph and 140.54 mg/l in plasma were reached within the first hour after a single intravenous dose of 100 mg/kg. The CSF mean peak level of 5.36 mg/l, however, was not attained until 3 h after injection. The half-life was about 4 h in perilymph, more than 6 h in CSF and less than 2 h in plasma. Six hours following administration, the perilymph drug concentration remained higher than the plasma level. The study indicates that ceftazidime has excellent penetration into perilymph. It is concluded that ceftazidime should be a very useful agent in the treatment of bacterial labyrinthitis caused by susceptible organisms.

Comparative serum bactericidal activity against Pseudomonas aeruginosa of six antipseudomonal agents

Serum levels and serum bactericidal activities of six antipseudomonal agents were studied comparatively in 60 patients. Single intravenous doses of gentamicin (1.5 mg/kg), piperacillin (4 g), ceftazidime (1 g), imipenem (0.5 g), aztreonam (1 g), and ciprofloxacin (200 mg) were given over 30 min to 10 patients each, and serum samples were obtained 30 min, 1, 2, 3, 4, 6, 8 and 12 h after beginning the infusion. Serum bactericidal activity was determined by the broth microdilution method against 10 recent isolates of Pseudomonas aeruginosa. Mean peak serum levels were as follows: gentamicin 10.4 micrograms/ml, piperacillin 227.5 micrograms/ml, ceftazidime 43.5 micrograms/ml, imipenem 17.3 micrograms/ml, aztreonam 42.3 micrograms/ml, and ciprofloxacin 3.9 micrograms/ml. All agents demonstrated effective serum bactericidal activity (geometric mean titer > 1:2) at peak serum levels. Ceftazidime was by far the most potent compound with a mean titer of 1:46.5, followed by ciprofloxacin (1:17), imipenem (1:13.7), and aztreonam (1:13.4). Ceftazidime also showed the longest duration of activity with a mean titer of 1:5.1 at 4 h. Based on our results, ceftazidime appeared to be the most potent antipseudomonal agent, while gentamicin and piperacillin were the least effective.

On-line solid-phase extraction of ceftazidime in serum and determination by high-performance liquid chromatography

A column-switching high-performance liquid chromatographic assay is described for the determination of ceftazidime (a third-generation cephalosporin) in human serum. The method does not require prior sample pretreatment. Serum is directly injected in a first chromatographic column for sample clean-up and extraction. Thereafter, using an on-line column-switching system, the drug is quantitatively transferred and separated on a second, analytical column followed by determination using ultraviolet absorption at 258 nm. The technique allows direct, rapid, precise, and simple determination of ceftazidime in serum over the range of 1-250 micrograms/ml using 12.5 microliters of serum. This method was applied to study the pharmacokinetics of the drug in patients undergoing vascular surgery.

[Critical serum concentration of antibiotics. A therapeutic tool and means of comparative evaluation]

It is difficult to predict the clinical activity of antibiotics solely on the basis of in vitro data. Experimental models measuring the relationship between serum concentration and in vivo activity are essential for comparing the activity of different compounds currently available. The critical serum concentration can be used to compare the intrinsic activity of antibiotics on a given bacterial strain. When compared with the minimal inhibiting concentration measured in vitro, "activity loss" can be determined for each antibiotic placed in contact with bacteria in an infected tissue. The relevance of this therapeutic tool in comparison with other methods is discussed.

Efficacy of gentamicin or ceftazidime entrapped in liposomes with prolonged blood circulation and enhanced localization in Klebsiella pneumoniae-infected lung tissue

Polymer (PEG-PE)-coated liposomes exhibit prolonged circulation time in blood and substantial localization in Klebsiella pneumoniae-infected lung tissue in rats. Therefore, to determine the therapeutic effect, gentamicin and ceftazidime were entrapped in these liposomes and administered to rats experimentally infected with pneumonia: Relatively high and sustained concentrations of liposome-associated antibiotic in blood were observed. Compared with antibiotics alone, one dose of liposome-entrapped gentamicin or ceftazidime increased the therapeutic effect of the drugs, survival of rats, and bacterial killing in lungs. One dose of liposome-entrapped ceftazidime was as effective as a continuous 2-day infusion of nonentrapped ceftazidime. Since antibiotic-containing liposomes are stable during circulation and liposome-entrapped ceftazidime and gentamicin have low bactericidal activity in vitro, the superior therapeutic effect of the liposome-encapsulated antibiotics results from localization and subsequent degradation of liposomes and the resulting release of entrapped antibiotic at the infection site.

Pulmonary penetration of ceftazidime

For an antibiotic to be effective in lower respiratory tract infections, it should be available in adequate concentrations in respiratory tissues and fluids. Cephalosporins usually achieve modest concentrations in the respiratory tract. In this study we have determined the pulmonary penetration of intramuscularly administered ceftazidime (a single dose of 1 g). Levels of ceftazidime in bronchial secretions (BS), bronchial mucosa (BM), epithelial lining fluid (ELF), and serum (S) were measured by microbiological assay in 25 patients suffering from acute exacerbation of chronic bronchitis who were divided into 5 groups of 5 subjects according to sampling time (1, 2, 4, 8 and 12 hours after the administration of the antibiotic). The peak S level was high (39.89 +/- 10.42 micrograms/ml at 1 hour) and mean S concentrations decreased slowly and were still detectable at 12 hours (1.07 +/- 0.45 microgram/ml). In all other samples, mean concentrations were in excess of the ceftazidime minimum inhibitory concentrations (MICs) for many relevant respiratory pathogens (Haemophilus influenzae 0.15 microgram/ml; Moraxella catarrhalis 0.06 micrograms/ml; Streptococcus pneumoniae 0.15 micrograms/ml; Klebsiella pneumoniae 0.4 microgram/ml). Concentrations in BM (7.05 +/- 2.38, 8.14 +/- 2.23, 6.40 +/- 1.63, 4.06 +/- 0.99 and 0.45 +/- 0.27 microgram/g) were higher than that in BS (6.87 +/- 1.96, 6.54 +/- 1.84, 3.52 +/- 1.23, 1.56 +/- 0.92 and 0.23 +/- 0.19 microgram/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Renal elimination of ceftazidime during pregnancy

OBJECTIVE

Our purpose was to study the pharmacokinetics of ceftazidime at different stages of pregnancy and in the nonpregnant state to determine whether glomerular filtration rate is altered and whether tubular secretions occurs.

STUDY DESIGN

Twelve pregnant women with asymptomatic bacteruria were given a bolus dose of 400 mg of ceftazidime followed by a constant infusion for 4 hours. Inulin was infused simultaneously to determine glomerular filtration rate. Blood samples were drawn every 30 minutes. Urine was collected immediately after the bolus dose and then every hour. The same study procedure was then repeated twice: 2 weeks before the expected delivery and after termination of breast-feeding.

RESULTS

At term clearance values were raised by 50% to 100% compared with the values found in the postpartum period. At all observation points a close correlation between inulin and ceftazidime clearance values were found.

CONCLUSION

The results strongly indicate that ceftazidime is excreted exclusively by glomerular filtration with no tubular reabsorption. During pregnancy the excretion pattern is unaltered, but renal elimination is increased.

The renal clearance of cefuroxime and ceftazidime and the effect of probenecid on their tubular excretion

1. The renal tubular excretion of cefuroxime and ceftazidime in relation to the coadministration of probenecid was investigated in eight and two healthy subjects, respectively. 2. Cefuroxime or ceftazidime were administered by i.v. infusion and 1 g probenecid was administered orally after steady state plasma concentrations of the cephalosporin were reached. 3. In a second session the same antibiotic was administered at increasing infusion rates such that three different levels of plasma drug concentration were achieved. 4. The renal clearance of antibiotic was calculated based upon unbound plasma concentration, and tubular clearance was estimated by subtracting inulin clearance from the renal clearance of the antibiotic. 5. Non-linear regression analysis was used to estimate parameters describing the saturability of tubular excretion and the effect of probenecid inhibition, i.e. EC50 and Rtub,max, could be established for cefuroxime: EC50 was 248 (s.d. 130) mg l-1 and Rtub,max was 1.852 (s.d. 0.577) mg h-1. Tubular excretion of ceftazidime was practically zero. The EC50 of probenecid for inhibition of the tubular excretion of cefuroxime was 0.80 (s.d. 0.31) mg l-1. 6. The results indicate that in the therapeutic plasma concentration range of cefuroxime its renal clearance is not saturated. Probenecid at therapeutic doses will block tubular excretion of cefuroxime almost completely.

Penetration of ceftazidime into human pancreas

The use of antibiotics in patients with severe acute pancreatitis (stage II and III) is indicated since bacterial complications are the most common cause of death in these patients. In the present study the penetration of ceftazidime into pancreatic juice, into healthy and chronically inflamed pancreatic tissue as well as into necrotic regions in cases of severe acute pancreatitis was investigated. A peak concentration of 12.9 +/- 5.9 mg/l was found 60 min after intravenous administration of 35 mg/kg of the drug, which is 32% of the corresponding serum levels. Pancreatic tissue concentrations varied between 9 and 79% of the corresponding serum levels, depending on the stage of inflammation. After five days of antibiotic treatment with doses of 2 g t.i.d., concentrations between 1.8 and 6.9 mg/kg were detected even in pancreatic necroses. This suggests that sufficient antibacterial levels of ceftazidime were present in all pancreatic compartments analyzed following administration of common therapeutic dosages. Therefore, from a pharmacokinetic point of view, ceftazidime could be a potentially effective drug for the treatment of pancreatitis.

Double beta-lactam regimen compared to an aminoglycoside/beta-lactam regimen as empiric antibiotic therapy for febrile granulocytopenic cancer patients

In a prospective, randomized trial, 205 febrile episodes in granulocytopenic cancer patients were treated with ceftazidime with or without tobramycin (C +/- T), both agents being administered only if the initial granulocyte count was below 200/microliters, or ceftazidime plus piperacillin (C + P). The overall response rate was 71% (39 of 60 for C +/- T and 45 of 58 for C + P). Logistic regression analyses documented no evidence of a significant difference between the two regimens in overall treatment effect after accounting for the linear effects of potentially important variables, such as infection type and granulocyte count. Although the response rates for the subgroup of patients with bacteremias was better with the C + P regimen (P = 0.06), there was no difference in response for patients with bacteremia and profound (< 100/microliters) sustained granulocytopenia. The double beta-lactam combination demonstrated in vitro synergism in 73%; antagonism was not seen. Both regimens produced excellent serum bactericidal levels (C +/- T geometric mean peak 1:170; C + P peak 1:137) against gram-negative but not gram-positive pathogens (1:4; 1:7 respectively) that had caused bacteremia. Emergence of resistance and significant coagulopathy and/or bleeding did not occur during therapy. Antibiotic-related nephrotoxicity was noted in 7 of 95 trials in the C + P and in 6 of 89 trials in the C +/- T group (P = 0.19). The incidence of secondary infections in patients with profound (< 100/microliters) sustained granulocytopenia was lower in the C +/- T group (P = 0.04). Alimentary canal anaerobic flora preservation with C +/- T, and suppression with C + P, was demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of ceftazidime and aztreonam alone or in combination with amikacin in experimental left-sided Pseudomonas aeruginosa endocarditis

The in vivo efficacies of ceftazidime, aztreonam, and the combinations of ceftazidime with amikacin and aztreonam with amikacin were studied in the rabbit left-sided endocarditis model by using two strains of Pseudomonas aeruginosa, one multisusceptible and one multiresistant, in a total of 156 animals. Antibiotics were given intramuscularly for 10 days, as follows: amikacin, 7 mg/kg of body weight every 8 h, and ceftazidime and aztreonam, 50 mg/kg every 8 h. All regimens except amikacin alone significantly reduced the number of CFU per gram of vegetation (P < or = 0.008), but only for the multisusceptible strain for which sterile vegetations were obtained in 20, 25, 21, 75, and 53% of the groups treated with amikacin, ceftazidime, aztreonam, and the combination groups ceftazidime-amikacin and aztreonam-amikacin, respectively (ceftazidime plus amikacin versus controls, P = 0.001). Regarding the decrease in the numbers of colonies in vegetations, (i) all regimens significantly reduced the number of CFU per gram of vegetation (P < 0.001), (ii) results with ceftazidime-amikacin compared with those with monotherapy were significantly different (P < or = 0.007), and (iii) results with aztreonam-amikacin, although better than those with monotherapy, were marginally not statistically significant. At 1 h postdose, mean amikacin, aztreonam, and ceftazidime levels in serum were 35 +/- 19.4, 89.6 +/- 8.16, and 92.61 +/- 11.52 micrograms/ml, respectively. It was concluded that the combination of ceftazidime, and possibly aztreonam, with amikacin given at high doses and short intervals could have a place in the therapy of patients with left-sided endocarditis caused by P. aeruginosa.

Comparison of the antibacterial effects of cefepime and ceftazidime against Escherichia coli in vitro and in vivo

The efficacies of cefepime and ceftazidime in an experimental Escherichia coli infection in granulocytopenic mice were related to their in vitro activities and their pharmacokinetic profiles. Cefepime had a higher intrinsic activity in vitro than ceftazidime, and it had a different pharmacokinetic profile, resulting in higher peak concentrations in plasma and a longer elimination half-life. To predict the antibacterial efficacy in vivo on the basis of in vitro activity and pharmacokinetics, we applied a mathematical model in which the in vitro effect is expressed as the difference in growth rate between control cultures and cultures grown in the presence of the antibiotic (ER), whereas the in vivo effect is given by the difference in the number of CFU between controls and antibiotic-treated animals (EN). The integral of ER over time, called ERt, was calculated by using in vivo concentrations. A significant linear relationship was found between EN and ERt for different doses at various times up to 4 h after administration, although the slope of this relationship was slightly but significantly less for cefepime (0.44) than for ceftazidime (0.59).

Bactericidal activity of cefclidin (E1040) against Pseudomonas aeruginosa under conditions simulating plasma pharmacokinetics: lack of development of chromosomally-mediated resistance to beta-lactams

The bactericidal activity of cefclidin (E1040), a new cephalosporin, against Pseudomonas aeruginosa was compared with that of ceftazidime and imipenem in an in-vitro model in which antibiotic concentration was varied continuously. A two-compartment open in-vitro model was used to simulate the plasma pharmacokinetics of each antibiotic in man for 12 h after a 1 h infusion of 1 g iv. The bactericidal activity of each antibiotic was observed for 6 h; however, it was diminished or absent after 6 h when the antibiotic concentration fell near to the MIC. With ceftazidime and imipenem, marked regrowth was observed after 6 h. Moreover, selection of resistant variants was observed with ceftazidime, and these variants produced 200 to 500 times more beta-lactamase than the corresponding wild-type strains. With cefclidin neither marked regrowth nor emergence of resistant variants was observed. The affinity of cefclidin for the chromosomal beta-lactamase produced by P. aeruginosa was much lower than the affinities of other new beta-lactams, and cefclidin was hydrolyzed more slowly than ceftazidime at a low concentration (2 microM). The high activity of cefclidin against P. aeruginosa, which results mainly from the low affinity of cefclidin for the pseudomonal beta-lactamase, and may play a major role in the absence of regrowth and lack of selection of resistant variants.

Comparative study of pharmacokinetics and serum bactericidal activities of cefpirome, ceftazidime, ceftriaxone, imipenem, and ciprofloxacin

We compared the pharmacokinetics and the serum bactericidal activities of cefpirome, ceftazidime, ceftriaxone, imipenem, and ciprofloxacin. Fifteen healthy volunteers received 1 g of cefpirome, ceftazidime, and ceftriaxone intravenously, 500 mg of imipenem-cilastatin intravenously, and 500 mg of ciprofloxacin orally. High-performance liquid chromatographic assays were used to quantitate unchanged antibiotic in plasma and urine. Serum bactericidal activities were determined against six clinical isolates each of Staphylococcus aureus, Enterobacter cloacae, and Pseudomonas aeruginosa by using a modified microdilution method of Reller and Stratton (L. B. Reller and C. W. Stratton, J. Infect. Dis. 136:196-204, 1977). Overall, cefpirome exhibited pharmacokinetics similar to those of ceftazidime: half-life (t1/2), 1.95 h; concentration at 1 h (C1h), 47 to 49 micrograms/ml for both antibiotics. Ceftriaxone displayed the longest t1/2 (7.65 h) and the highest C1h (137.8 micrograms/ml), while we observed the shortest t1/2 (1.05 h) and the lowest C1h (19.85 micrograms/ml) with imipenem. At 1 h, cefpirome and, even more so, imipenem showed significantly better serum bactericidal activities against S. aureus (1:273 and 1:80) than did the other antibiotics (P less than 0.0005; analysis of variance with randomized block design and Bonferroni correction). Against E. cloacae, we observed the highest serum bactericidal titers at 1 h with cefpirome, and this superiority vis-à-vis the other antibiotics tested was maintained for up to 8 h after dosing. Ceftazidime remained the most active agent tested against P. aeruginosa (serum bactericidal activity titers, 1:43 at 1 h) up to 8 h. In summary, the study showed that cefpirome and imipenem provide more potent serum bactericidal activities than do broad-spectrum cephalosporins against S. aureus; thus, both of these antibiotics should be adequate against serious S. aureus infections. In addition, cefpirome appears to be a promising alternative for treatment of infections caused by E. cloacae and P. aeruginosa.

[Age-related characteristics of ceftazidime pharmacokinetics in children]

To reveal possible age-dependent variations in the ceftazidime pharmacokinetics, the drug plasma concentrations were determined by HPLC in 10 children aged 2 to 13 years with peritonitis. The blood specimens were collected 0.25, 0.5, 1, 3, 6 and 8 hours after intravenous bolus administration of ceftazidime (Kefadym, Eli Lilly) in a single dose of 20 mg/kg. The mean values of the model-independent parameters were: total clearance (Cl), 3.3 +/- 0.8 ml/min.kg; steady-state distribution volume, 0.32 +/- 0.06 ml/kg; mean residence time, 1.7 +/- 0.4 hours. The C-coordinate of the gravity center was equal to 26 +/- 7 mg/l. A noticeable age-dependent decrease in Cl was detected by comparing the Cl estimates in our study for the children aged 7.0 +/- 3.0 years with earlier findings in children aged 12 years as well as in adults (18 and 26 years) and elderly patients (77 years): 2.5, 2.2, 2.0 and 1.1 ml/min.kg, respectively. A similar trend was observed for the ceftazidime volume of distribution (Varea). Due to the described reduction in Cl and Varea the age-induced changes in the half-life of ceftazidime were negligible. The age-dependent differences in ceftazidime pharmacokinetics should be taken into account in designing rational dosage regimens for the drug administration.

Determination of ceftazidime in dolphin serum by liquid chromatography with ultraviolet-visible detection and confirmation by thermospray liquid chromatography-mass spectrometry

A simple and sensitive liquid chromatographic method has been developed for the determination of therapeutic levels of ceftazidime in dolphin serum. The method involved an ultrafiltration of diluted serum with an equal amount of acetonitrile-ethanol-water (40:40:20, v/v/v) through a 10,000 daltons molecular mass cut-off filter. Separation of ceftazidime from the other serum components was performed by ion-paired (dodecanesulfonate) liquid chromatography using a reversed-phase column eluted with acetonitrile-water solution. The ultraviolet absorbance of the column effluent was monitored in the 200-340 nm range of a photodiode-array detector or at 258.8 nm on a variable-wavelength ultraviolet-visible detector. Recoveries of ceftazidime from dolphin serum spiked with 20 and 2 micrograms/ml were 92.9 and 91.1% with coefficients of variation of 5.5 and 5.7%, respectively. A correlation coefficient of 0.9994 occurred with ceftazidime in aqueous solutions (n = 6, in duplicates). The limit of detection for this antibiotic was estimated to be approximately 50 ppb (ng/ml). The unbound ceftazidime concentrations in dosed dolphin serum were determined to calculate the protein bindings of this antibiotic which yielded 32 +/- 2%. The ceftazidime peak identity in dosed dolphin serum was confirmed by thermospray liquid chromatography-mass spectrometry. The thermospray mass spectrum of ceftazidime exhibited only the fragment ions, involving the opening of the beta-lactam ring, at m/z 237, 255 and 315 when positive-ion detection mode was employed and the fragment ions at m/z 235, 253 and 313 when negative-ion detection mode was used.

Pharmacokinetics of ceftazidime in acutely ill hospitalised elderly patients

The i.v. and i.m. dose pharmacokinetics of ceftazidime 1 g b.i.d. were investigated in steady state in 52 consecutive cases of hospitalised patients with underlying diseases and serious supervening bacterial infections. Following i.v. bolus injection, serum concentrations of greater than 4 mg/l persisted for 8 h in all patients. Compared to values found in younger patients studied previously, clearance was markedly reduced in the elderly, t1/2 beta more than doubled, the area under the curve four times enlarged and the apparent volume of distribution reduced. The values obtained in serum after i.m. injection were similar, though the peak concentration was delayed by about 2 h. The serum uptake was approximately 70%, and serum concentration was greater than 4 mg/l for 8 h. The concentrations in tissue fluid after i.v. administration were similar to those in serum, but the penetration into tissue fluid was slower and only 20% of that reported previously for young people. The elimination was slow, with greater than 4 mg/l maintained for 7 h. Tissue concentrations after i.m. injection were almost comparable with those after i.v. injection, but lagged behind by about 1 h. In conclusion, suitable concentrations in blood and tissue are attained with 1 g ceftazidime b.i.d., whether administered by the i.v. or i.m. route.

[Ceftazidime concentration in human prostatic tissue and serum following intravenous injection]

The present study was undertaken to evaluate the penetration of Ceftazidime (CAZ) into prostatic tissue (P) and serum (S). Thirty-seven patients with benign prostatic hypertrophy took part in this study. CAZ was administered intravenously at a dose of 1g preoperatively. Blood samples were taken simultaneously at the time of tissue sampling by transurethral resection of the prostate (TUR-P). The patients were divided into 3 groups. In group 1 (twelve patients), intravenous injection of the drug was given 60 minutes before tissue sampling. The mean concentrations of CAZ were 23.4 +/- 7.4 micrograms/g in the prostatic tissue and 45.0 +/- 15.9 micrograms/ml in the serum. In group 2 (thirteen patients), the injections were given 120 minutes before tissue sampling. The mean concentrations of CAZ were 18.0 +/- 8.2 micrograms/g in the prostatic tissue and 39.8 +/- 21.3 micrograms/ml in the serum. In group 3 (twelve patients), the injections were given 240 minutes before tissue sampling. The mean concentrations of CAZ were 11.3 +/- 3.2 micrograms/g in the prostatic tissue and 22.3 +/- 9.6 micrograms/ml in the serum. These findings indicate that CAZ is useful for the treatment of prostatitis and preventive medication before TUR-P.

Ceftazidime as monotherapy or combined with teicoplanin for initial empiric treatment of presumed bacteremia in febrile granulocytopenic patients

In a prospective randomized study, 120 febrile, granulocytopenic patients received as initial therapy ceftazidime with or without teicoplanin. At the onset of fever, patients had no obvious infectious focus. For 103 assessable episodes, initial bacteremias were detected in 18 of 51 patients (35%) given ceftazidime and 20 of 52 patients (38%) given the combination; 13 and 17 bacteremias caused by gram-positive bacteria occurred in these groups, respectively. There was no difference in terms of the final response (25 of 51 patients [49%] treated with ceftazidime alone versus 33 of 52 patients [63%] given the combination), and the morbidity was comparable for both treatment groups. The duration of fever and of total antibiotic therapy were similar in both groups. Initial therapy was modified in 26 patients (51%) treated with ceftazidime, with 20 surviving the infection, and in 19 patients (37%) treated with the combination, with 15 surviving. Persistent fever was the main reason for changing treatment, and no patient died of a gram-positive infection. Subsequent infective events occurred in 16 patients (31%) given ceftazidime and in 25 patients (48%) given the combination. Lung infiltrates developed in 12 and 13 patients, respectively, but more new infections occurred in the combination group. Allergic skin reactions were also more frequent in this group. Thus, while teicoplanin provides simple, reliable, and safe treatment of patients with presumed gram-positive infections, it is not useful when given empirically to this patient population, and treatment may result in more infective complications and adverse events.

Pharmacokinetics of ceftazidime in serum and suction blister fluid during continuous and intermittent infusions in healthy volunteers

The pharmacokinetics of ceftazidime were investigated during intermittent (II) and continuous (CI) infusion in eight healthy male volunteers in a crossover fashion. The total daily dose was 75 mg/kg of body weight per 24 h in both regimens, given in three doses of 25 mg/kg/8 h (II) or 60 mg/kg/24 h with 15 mg/kg as a loading dose (CI). After the third dose (II) and during CI, serum and blister fluid samples were taken. Seven new blisters were raised for each timed sample by a suction blister technique. Blisters took 90 min to form. Samples were then taken from four blisters (A samples) and 1 h later were taken from the remaining three (B samples). The concentration of ceftazidime was determined using a high-performance liquid chromatography method. After II, the concentrations in serum immediately after infusion (t = 30 min) and 8 h after the start of the infusion were 137.9 (standard deviation [SD], 27.5) and 4.0 (SD, 0.7) micrograms/ml, respectively. The half-life at alpha phase (t1/2 alpha) was 9.6 min (SD, 4.6), t1/2 beta was 94.8 min (SD, 5.4), area under the concentration-time curve (AUC) was 285.4 micrograms.h/ml (SD, 22.7), total body clearance was 0.115 liter/h.kg (SD, 0.022), and volume of distribution at steady state was 0.178 liter/kg (SD, 0.023). The blister fluid (A) samples showed a decline in concentration parallel to that of the concentrations in serum during the elimination phase with a ratio of 1:1. The t1/2 of the A samples was 96.4 min (SD, 3.2). The concentration of ceftazidime in the B blister fluid samples was significantly higher (27%) than in the A samples over time. This shows that blisters may behave as a separate compartment and establishes the need to raise new blisters for each timed sample. The mean AUC/h during continuous infusion was 21.3 micrograms . h/ml (SD, 3.0). The total body clearance was 0.113 liter/h . kg (SD, 0.018), the urinary clearance was 0.105 liter/h . kg (SD, 0.012), and the ceftazidime/creatinine clearance ratio was 0.885. The mean AUC of blister fluid per hour was 84.5% (18.0 micrograms . h/liter; SD, 3.6) compared with that of serum. The A samples did not differ significantly from the B samples. The implications of continuous infusion of beta-lactams for treatment of serious infections are discussed.

Comparative study of the effects of four cephalosporins against Escherichia coli in vitro and in vivo

A thigh muscle infection induced with Escherichia coli in irradiated mice was used as a model to compare the in vivo pharmacodynamics of the antibacterial effect of four cephalosporins (i.e., cefepime, ceftriaxone, ceftazidime, and cefoperazone) with the in vitro antibacterial pharmacodynamics of these drugs. The following in vitro pharmacodynamic parameters were determined: the maximum effect as a measure for efficacy, the 50% effective concentration as a parameter for potency, and the slope of the concentration-effect relationship. For analysis of the in vivo antibacterial pharmacodynamics, the same parameters were applied for the dose instead of the concentration. For the detection of a relationship between concentration and antibacterial effect in vivo, we determined the pharmacokinetics of the four cephalosporins in the plasma of mice. The results showed that, in general, there is a direct relationship between the in vivo and in vitro pharmacodynamics of these cephalosporins. The maximum effects of cefepime, ceftazidime, and cefoperazone were approximately similar in vivo and in vitro. The sequence of potency of these drugs was, in descending order, cefepime, ceftazidime, and cefoperazone. Ceftriaxone differed from the other three cephalosporins in that it displayed unexpected in vivo pharmacodynamics. Ceftriaxone was just as efficacious as the other three in vitro, but its maximum effect in vivo was much lower. This relatively low maximum effect of ceftriaxone in vivo was not explained by the pharmacokinetic characteristics of the drug. From the present results it can be concluded that the in vitro efficacy of cephalosporins does not necessarily have a predictive value for the in vivo efficacy.

The effect of obstruction on the biliary excretion of cefoperazone and ceftazidime

The biliary excretion of cefoperazone and ceftazidime was studied by endoscopic cannulation of the common bile duct, in patients with complete biliary obstruction and in an unobstructed control group. Patients were given each drug prophylactically for 24 h before endoscopy and as a single dose at the time of cannulation. In unobstructed patients biliary excretion of ceftazidime was passive. At the time of cannulation bile contained 10% of the peak serum concentration, rising to 20% 90 min later. Cefoperazone excretion was active. At cannulation biliary concentrations were 200% of the serum peak, 900% at 60 min and 700% at 90 min. In obstructed patients, bile sampled immediately at decompression contained neither antibiotic. Passive excretion of both drugs occurred rapidly after relief of obstruction and biliary concentrations were 20% of maximum serum levels at 60 min. Twenty-four hours later passive excretion had further improved, but the active excretion mechanism of cefoperazone had still not recovered. We conclude that obstruction impairs active as well as passive biliary excretion of antibiotics, that drainage is essential for the control of sepsis in obstructed cholangitis, and that both cefoperazone and ceftazidime achieve similar and therapeutic concentrations in bile during the 24 h after decompression.

Relevance of protein binding to cephalosporin antimicrobial activity in vivo

Protein binding, serum kinetics and minimum inhibitory concentrations (MICs) for Staphylococcus aureus were determined for cefoxitin, cefazolin, ceftazidime and ceftriaxone in the rabbit. MICs of cefazolin and cefoxitin were also measured for Escherichia coli. Varying concentrations of the bacteria were administered intradermally to create areas of cellulitis, which were quantified as mean erythematous areas (EAs). Despite large differences in protein binding of the antibiotics (range 12-88%) and antibiotic dosing to allow serum concentrations to drop below the respective MICs, there was no statistical difference in the mean EAs of the animals after bacterial challenge. Antibiotic protein binding did not alter the course of cellulitis nor correlate with bacterial MIC in this model.

[Serum and cerebrospinal fluid kinetics of ceftazidime]

Ceftazidime serum concentrations and cerebrospinal fluid (CSF) penetration across non-inflamed meninges were evaluated in 10 patients after intravenous application of 2 g ceftazidime over a period of 30 min. After a continuous increase during infusion the highest level of ceftazidime in serum with 172.27 micrograms/ml (+/- 60.43 micrograms/ml) was ascertained at the end of the infusion. The further development demonstrated a continuous decrease of serum concentrations. Concentrations in serum followed a two-compartment open kinetic model. Mean distribution volume was 17.6 l, the total clearance was 142.97 ml/min, half-life was 1.8 h and the determined area under the curve was 139.89 micrograms x min/ml. Penetration of ceftazidime into CSF could only be pointed out in 5 patients. The highest level with 5.11 micrograms/ml (+/- 1.2 micrograms/ml) was observed 32 min after starting the infusion. A steady state with CSF-concentrations over 2 micrograms/ml could be ascertained during the following 4 hours in these patients. Obviously high statistic significance (p less than or equal to 0.01) was present when penetration into CSF was correlated to body surface area (BSA) using the exact Fisher test with Yates correction. Penetration of ceftazidime into CSF across non-inflamed meninges with therapeutic concentrations over a period of 4 hours could only be achieved when BSA was less than 1.95 m2. Further investigations in more patients are necessary to evaluate if BSA is the only parameter which affects distribution of ceftazidime into CSF.

Pharmacokinetics of ceftazidime given alone and combination with probenecid to unweaned calves

Ceftazidime pharmacokinetic values were studied in unweaned calves given the antibiotic alone or in combination with probenecid. Ceftazidime was administered IV to 9 calves at a dosage of 10 mg/kg of body weight and IM (10 mg/kg) to 8 calves, to 7 calves (10 mg/kg plus probenecid [40 mg/kg]), and to 9 calves (10 mg/kg plus probenecid [80 mg/kg]). Serum concentration-vs-time data were analyzed, using noncompartmental methods based on statistical moment theory. The data for IV ceftazidime administration also were fitted by use of a linear, open 2-compartment model. The mean (+/- SD) terminal half-life was 138.7 +/- 23.6 minutes and 126.3 +/- 10.5 minutes after IV and IM administrations, respectively. The mean residence time was 167.3 +/- 21.1 minutes and 201.4 +/- 16.8 minutes after IV and IM administrations, respectively. Coadministeration of probenecid did not affect the terminal half-life or mean residence time values. The total body clearance was 1.75 +/- 0.26 ml/min/kg, and the volume of distribution at steady state was 0.294 +/- 0.064 L/kg. The estimated mean absorption time was 34.1 minutes. There were no significant differences between the mean residence time calculated by statistical moment theory or by compartmental analysis, indicating central compartment output of ceftazidime. The 90% minimal inhibitory concentration values of ceftazidime determined for Escherichia coli, Salmonella spp, Pasteurella multocida, and P haemolytica isolates ranged from less than 0.01 to 0.1 micrograms/ml.

[Treatment of peritonitis under continuous ambulatory peritoneal dialysis using intraperitoneal ceftazidime]

Management of peritonitis related to chronic ambulatory peritoneal ceftazidime. In 15 patients under CAPD, 22 cases of bacterial peritonitis were observed with clinical manifestation in 14. The mean cell count in peritoneal dialysis fluid was 3 580/mm3 with 3 040/mm3 polymorphonuclear leukocytes. Causative pathogens were: Staphylococcus in 11 cases, Streptococcus in 3, Sarcines in 2, Corynebacterium in 2, Micrococcus varians in 1, Gram negative in 3. First choice treatment was a intraperitoneal injection of 1 g of ceftazidime every 48 hours, 54.5% of patients recovered within 5 days. Failures were due to 4 Staphylococcus aureus, 3 Staphylococcus epidermidis, 1 Sarcine, 1 Streptococcus liquefaciens, 1 Corynebacterium hofmanii. Mean ceftazidime concentrations 48 hours after the intraperitoneal injection were 35 mg/l (range = 14-54 mg/l) in serum and 5.5 mg/l (E: 2.8,8 mg/l) in dialysate. These concentrations in dialysate, are not greater than most of ceftazidime'S CMI for susceptible bacteria. A single daily intraperitoneal injection of ceftazidime is desirable.

[Study on CAZ levels in serum, urine and myocardial tissue during and after open-heart surgery with cardiopulmonary bypass]

Ceftazidime (CAZ) was administered to 10 patients who underwent open heart surgery using an artificial heart and lung (AHL), and the concentrations of the drug in the blood, urine, filtrate and cardiac muscle were measured. Following anesthesia induction, patients were injected intravenously with 2 g CAZ, and then 2 g CAZ was injected initially into the filling solution of the AHL followed by 1 g every 1 hr. After the surgery, patients received 1 g CAZ intravenously followed by the same dose every 12 hr till Day 5 of the surgery. Results obtained were as follows: 1) The concentration of CAZ in the cardiac muscle averaged 41.2 +/- 12.3 micrograms/g, and the ratio to the concentration in the plasma averaged 0.61 +/- 0.12, being considered to be reasonable. 2) The change in the mean plasma concentration of CAZ during extracorporeal circulation was maintained within the range of 109.7 to 337.0 micrograms/ml, and the concentration increased slightly with the repeated injection. In 2 cases, the plasma concentration was transiently more than 400 micrograms/ml, however, no side effect was observed. 3) The mean plasma concentration of CAZ after surgery attained 214.4 +/- 38.9 micrograms/ml, and half-time averaged 2.8 hr. 4) The excretion rates of CAZ in urine and filtrate by the termination of the extracorporeal circulation were 30.6 and 5.2%, respectively, thus the excretion of the drug in filtrate was lower than that in urine. The total excretion rate in both urine and filtrate for 6 hr after surgery was 55.3%. 5) Neither postoperative infection nor side effect were observed in all cases. CAZ is considered to be a useful antibiotics in the cardiac surgery management.

Disposition of ceftazidime in surgical patients with intra-abdominal infection

The disposition of ceftazidime was assessed in 11 surgical patients with suspected intra-abdominal infection. All patients had normal hepatic function, and creatinine clearances ranged from 43 to 186 ml/min. Patients received 2 g of ceftazidime intravenously every 8 h. Trough and peak concentrations in serum were measured on day 2, and trough and postdose concentrations in serum were determined on 10 samples collected during a dosage interval between days 3 and 6 of therapy. Ceftazidime peak and trough concentrations in serum at steady state determined by high-performance liquid chromatography were 257.4 +/- 122.0 (mean +/- standard deviation) and 13.1 +/- 20.6 mg/liter. The serum-concentration-versus-time profile was multiexponential. The elimination half-life, steady-state volume of distribution, and total body clearance were 2.52 +/- 1.39 h, 0.31 +/- 0.12 liter/kg, and 0.11 +/- 0.05 liter/h per kg, respectively. Total predicted body clearance significantly correlated with the measured values (r = 0.868; P = 0.001). The disposition of ceftazidime is dependent on creatinine clearance and is not significantly altered by surgery or acute infectious processes.

An evaluation of optimal sampling strategy and adaptive study design

We have evaluated the utility of optimal sampling strategy coupled with adaptive study design in the determination of individual patient and population pharmacokinetic parameter values. In 9 patients with cystic fibrosis receiving a short (1 minute) infusion of ceftazidime pharmacokinetic parameter values were determined with a nonlinear least-squares estimator analyzing a traditional, geometrically spaced set of 12 postinfusion serum samples drawn over 8 hours. These values were compared with values generated from four sample subsets of the 12 obtained at optimal times and analyzed by nonlinear least-squares estimator, as well as a maximum a posteriori probability Bayesian estimator with prior distributions placed on beta and clearance. The four sampling times were determined according to an adaptive design optimization technique that employs sequential updating of population prior distributions on parameter values. Compared with the 12-point determination, the four optimal points analyzed with the maximum a posteriori probability Bayesian estimator faithfully reproduced both microscopic and hybrid pharmacokinetic parameter values for individual patients and, consequently, also produced accurate measures of population central tendency and dispersion. This has important implications in being able to more efficiently derive target patient population pharmacokinetic information for new drugs. This should also allow generation of better concentration-effect relationships in populations of interest.

Ceftazidime combined with mecillinam: serum bactericidal titres compared with in-vitro synergy against gram-negative bacilli

In a study of the possible interaction between mecillinam and ceftazidime against Gram-negative bacilli, ten volunteers received on separate days: ceftazidime 20 mg/kg iv in 15 min, mecillinam 10 mg/kg iv in 15 min, or the combination. Blood samples were obtained before and 1 and 6 h after the end of the infusion. Ten strains each of Klebsiella pneumoniae, Serratia marcescens, Citrobacter freundii, Salmonella spp. and Yersinia spp. and nine strains each of Acinetobacter spp., and Pseudomonas aeruginosa were selected. Most of the strains were resistant to ampicillin and cefazolin. Serum levels of ceftazidime and mecillinam were measured by bioassay. Serum bacteriostatic (SBS) and bactericidal (SBA) titration was done in microtitre plates in cation supplemented Mueller-Hinton broth and 50% human serum. Chequerboard titration was also studied to assess in-vitro synergy between ceftazidime and mecillinam in Mueller-Hinton broth with or without 50% serum. The mean serum concentrations (SD) were for mecillinam: 6.1 (1.7) at 1 h, and less than 0.3 at 6 h and for ceftazidime: 36.3 (5.5) at 1 h and less than 5 at 6 h. Identical concentrations were measured for the combination. By chequerboard titration, no synergy occurred for Acinetobacter spp. and Ps. aeruginosa, whereas it was observed in 37/60 (FIC) and 33/60 (FBC) of the strains of other species in Mueller-Hinton; from the strains showing synergy, 28/37 (FIC) and 30/33 (FBC) showed also synergy in Mueller-Hinton with 50% human serum. In SBS and SBA, on the other hand, the combination of mecillinam with ceftazidime showed an additive effect against most Enterobacteriaceae tested, synergy being shown for only 10-35% of tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of serum concentrations of ceftazidime and tobramycin in newborn infants

Peak and trough serum concentrations of ceftazidime and tobramycin were determined in neonates with suspected septicaemia in an open randomized study. Mean peak serum levels were 85 (+/- 4.4 SE) mg/l for ceftazidime and 5.8 (+/- 0.3 SE) mg/l for tobramycin. The peak serum levels of ceftazidime were well above the reported minimal inhibitory concentration (MIC)90 values of pathogenic bacteria encountered in neonates, while peak serum levels of tobramycin were lower than reported MIC90 values for Klebsiella, Pseudomonas, Enterobacter and Serratia species. Nine of 33 tobramycin-treated patients had potentially toxic trough serum levels (greater than 2 mg/l) and nine had subtherapeutic peak serum levels (less than 4 mg/l). The dosage of this antibiotic had to be changed frequently. In comparison only 2 of 29 ceftazidime-treated patients had subtherapeutic peak levels (less than 40 mg/l) and none had potentially toxic trough levels (greater than 40 mg/l). Ceftazidime, in comparison with tobramycin, has a more favourable antibacterial spectrum and routine determinations of peak and trough serum levels should not be necessary.

Effect of protein binding on serum bactericidal activities of ceftazidime and cefoperazone in healthy volunteers

The effect of protein binding on antibiotic efficacy is controversial. The pharmacologic effect of an antibiotic is believed to be related to its unbound concentration at the site of infection. It is unknown whether antibiotics with a low degree of serum protein binding are clinically superior to antibiotics that are highly protein bound. In a randomized, crossover investigation, the serum bactericidal activities of a single dose of ceftazidime (30 mg/kg) and cefoperazone (30 mg/kg) were studied in six healthy volunteers against three clinical isolates of Pseudomonas aeruginosa for which both antibiotics had similar MICs and MBCs. Serum samples were collected over 12 h. The total and unbound antibiotic concentrations were determined by high-pressure liquid chromatography. Mean peak total concentrations of ceftazidime and cefoperazone in serum were 101.7 +/- 18.6 and 264.1 +/- 149.6 micrograms/ml, respectively. Due to its lower protein binding (21 +/- 6%), ceftazidime had significantly higher unbound concentrations in serum than did the highly bound cefoperazone (91.5 +/- 2%). Mean peak unbound concentrations were 78.5 +/- 12.5 and 24.2 +/- 17.8 micrograms/ml for ceftazidime and cefoperazone, respectively. The unbound concentration of ceftazidime at each sampling time was higher than that of cefoperazone. Although total concentrations were consistently higher than the MICs, serum containing cefoperazone showed minimal bactericidal activity against the isolates. In contrast, despite lower total concentrations, ceftazidime had greater antibacterial activity than cefoperazone. Serum bactericidal activity was more closely related to unbound rather than total antibiotic concentrations. Our data support the concept that only the unbound drug is microbiologically active.

The pharmacokinetics of ceftazidime in patients with impaired renal function and concurrent frusemide therapy

We have studied the pharmacokinetics of ceftazidime in 37 patients suffering from serious bacterial infections. All the patients had impairment of renal function and received moderate to high doses of frusemide concurrently. The doses of ceftazidime were given according to renal function as recommended by the manufacturer. Serum and urine samples were frequently collected, and drug concentrations measured by high performance liquid chromatography. The patients were grouped and evaluated according to renal function, mean (SD) creatinine clearances ranging from 70.1 (12.4) to 11.0 (3.2) ml.min-1. The pharmacokinetics of ceftazidime depended on renal function. A statistically significant increase in ceftazidime elimination half-life and decreases in urinary recovery, total body clearance, and renal clearance in proportion to the decrease in renal function were observed (p less than 0.05). The apparent volume of distribution also increased, but not significantly (p greater than 0.05). A linear correlation was found between the total body and renal clearances of ceftazidime and creatinine clearance. The extrarenal clearance increased from 3.9 to 14.0 ml.min-1 with decreasing renal function. Concurrent treatment with ceftazidime and moderate to high doses of frusemide did not impair renal function and no evidence of nephrotoxicity was found.

Influence of age on the pharmacokinetics of ceftazidime in acutely ill, adult patients

The single and multiple i.v. dose pharmacokinetics of ceftazidime were investigated in 37 acutely ill patients with normal age-related glomerular function. Distribution was rapid with similar t1/2 alpha at all ages. Compared to the younger patients, elderly subjects had lower total and renal clearances and reduced urinary recovery. Ceftazidime clearance was closely correlated with glomerular function. The t1/2 beta was approximately 2 h in young and middle-aged patients, 2.73 h in patients aged 60-79 years, and 3.54 h in those above 80 years. The AUC was more than doubled in the oldest patients compared to individuals younger than 40 years. Vss did not change with advancing age, but was larger than previously reported in healthy volunteers. Elimination variables were not altered during multiple dosing, but a small but significant increase in AUC was detected in the elderly. Dose reduction by 50% in patients more than 70 years old is suggested.

Penetration of cefuroxime and ceftazidime into human lungs

We have studied the penetration of cefuroxime and ceftazidime into lung tissue of 40 patients subjected to pulmonary surgery. Samples of blood and lung tissue were taken 1 and 2 h after antibiotic administration. Patients were randomly assigned to four dosage schedule groups: group A received a single intravenous injection of 750 mg cefuroxime; the lung tissue levels at 1 and 2 h were 9.6 +/- 3.1 and 4.54 +/- 2.64 micrograms/g of cefuroxime; the percentage penetration from serum into the lung tissue was 33.7 and 34.6%, respectively. Group B patients received three doses of 750 mg cefuroxime; lung tissue levels were 17.1 +/- 7.7 and 14.7 +/- 5.4 micrograms/g, the percentage of penetration being 89.1 and 102.8% at 1 and 2 h. Group C received a single intravenous injection of 1 g ceftazidime; the lung tissue levels were 16.3 +/- 10.1 and 10 +/- 5.04 micrograms/g; the percentage of penetration from serum was 38.3 and 35.3%. Group D received three doses of 1 g ceftazidime; the lung tissue concentrations were 11.98 +/- 7.5 and 8.5 +/- 7.3 micrograms/g and the percentage of penetration 35.1 and 32.2% at 1 and 2 h after last dose.

Pharmacokinetics and serum bactericidal activity of vancomycin alone and in combination with ceftazidime in healthy volunteers

The pharmacokinetics and serum bactericidal activity of vancomycin alone and in combination with ceftazidime were investigated in 10 healthy volunteers. The pharmacokinetic parameters showed no significant differences (P less than 0.05) between single and combined administration. No antagonistic effects were observed in serum bactericidal activity with the combination against 20 gram-positive and 20 gram-negative locally isolated bacteria. A titer of greater than or equal to 1:8 was generated by the combination against all test strains except enterococci. Seven of ten volunteers developed a typical "red man's syndrome" during the administration of 1.0 g of vancomycin.

Influence of dose frequency on the therapeutic efficacies of ciprofloxacin and ceftazidime in experimental Klebsiella pneumoniae pneumonia and septicemia in relation to their bactericidal activities in vitro

The antibacterial activities of ciprofloxacin versus ceftazidime against Klebsiella pneumoniae in vitro and in vivo were compared. Although there was only a minor difference in MBC values between both drugs ciprofloxacin demonstrated a high and dose-dependent bacterial killing rate in vitro and in lungs of leukopenic rats in contrast to the more time-dependent bactericidal activity of ceftazidime. After treatment of a K.pneumoniae pneumonia and septicemia the efficacy of ciprofloxacin was only slightly influenced by the mode of administration, either at 6-h intervals or continuously, whereas ceftazidime was far more effective after continuous administration. This resulted in a superior efficacy of ciprofloxacin after intermittent treatment as compared to ceftazidime, whereas ceftazidime was more effective after continuous administration as compared to ciprofloxacin. Also ciprofloxacin proved to be bactericidal against bacteria that were not actively growing, both in vitro and in vivo, whereas ceftazidime was not.