Serum bactericidal activity of ceftazidime and cefoperazone alone or in combination with amikacin against Pseudomonas aeruginosa and Klebsiella pneumoniae

Correlation of the Pharmacokinetic Parameters of Amikacin and Ceftazidime

BACKGROUND AND OBJECTIVES

Ceftazidime and amikacin are often prescribed concomitantly to treat infections caused by Gram-negative bacteria. Their physicochemical properties are quite similar. Both drugs are highly soluble in water, have low plasma protein binding and are >95% excreted unchanged by the kidney via glomerular filtration. Their pharmacokinetic parameters are therefore expected to correlate. This study was performed to explore the correlation between the pharmacokinetic parameters of these two drugs.

PATIENTS AND METHODS

Patients at Phramongkutklao Hospital, Bangkok, Thailand, who met the inclusion criteria participated in the study. They all received ceftazidime and amikacin concomitantly to treat their infections. After steady-state conditions had been reached, two blood samples were collected during the elimination phase of both drugs. Plasma drug concentrations were analysed and the pharmacokinetic parameters of each drug were calculated. The pharmacokinetic parameters that were examined included total drug clearance (CL), the elimination rate constant (k(e)), the elimination half life (t(1/2)) and the volume of distribution (V(d)). The correlations of the pharmacokinetic parameters of amikacin and ceftazidime were determined using regression analysis.

RESULTS

Regression analysis showed that the pharmacokinetic parameters of ceftazidime and amikacin were highly correlated. The correlation coefficients (r) of CL, k(e), t(1/2) and V(d) of the two drugs were 0.966, 0.943, 0.888 and 0.671, respectively. The correlation between amikacin clearance and ceftazidime clearance was higher than the correlation between either amikacin or ceftazidime clearance and creatinine clearance, for which the r values were 0.647 and 0.661, respectively.

CONCLUSIONS

The pharmacokinetic parameters of ceftazidime and amikacin were highly correlated. Knowledge of the pharmacokinetic parameters of one of these drugs can be used to predict the pharmacokinetic parameters of the other drug.

Cefepime versus ceftazidime + amikacin as empirical therapy for febrile neutropenia in children with cancer: a prospective randomized trial of the treatment efficacy and cost

The efficacy, safety, and cost of cefepime and ceftazidime + amikacin as empirical therapy in children with febrile neutropenia is compared. A prospective randomized study in children with cancer was conducted. Patients were randomly assigned to receive either cefepime 150 mg/kg/day or ceftazidime 150 mg/kg/day combined with amikacin 15 mg/kg/day. Treatment modification was defined as all the changes in the empirical antimicrobials after the first 72 h. Overall treatment success was defined as cure of febrile episode with or without modification. Costs of hospitalization, antimicrobial drugs, and supportive therapy were calculated. Fifty febrile netropenic episodes were evaluated. Infectious agents were microbiologically identified in 28% of episodes. The incidence of gram-negative and gram-positive isolates was equal. Overall treatment success was 100% and success of initial empirical therapy without modification was 52 and 40% in the cefepime and cefepime + amikacin groups, respectively. The response rate after glycopeptides were added to the regimen was 64 and 52 % in the cefepime and cefepime + amikacin arms, respectively. Glycopeptide and antifungal drugs were added more frequently in the ceftazidime + amikacin group. Duration of fever, hospitalization, and antimicrobial drug administration were longer in the ceftazidime + amikacin arm. The costs of the antimicrobial drugs, hospitalization, and total cost were lower in the cefepime arm. Cefepime monotherapy is as effective as ceftazidime + amikacin combination in febrile neutropenia of pediatric cancer patients and must be preferred due to shorter defervescence of fever, shorter hospitalization, and lower therapy cost.

Monotherapy versus combination therapy for bacterial infections

The authors discuss the latest findings regarding the use of one or more antimicrobial drugs for a variety of infections. They offer suggestions for treatment based on a host of considerations, including the synergy and antagonism of specific drugs, type of infection, potential toxicities, and cost.

Serum bactericidal activity after administration of four cephalosporins in healthy volunteers

Serum bactericidal activity (SBA) was determined against ten strains each of Staphylococcus aureus, Klebsiella pneumoniae, Proteus vulgaris and Enterobacter cloacae in six volunteers 1 h and 4 h after intravenous infusion of 1 g and 2 g cefotaxime and cefmenoxime, and 2 g flomoxef, and against ten strains of Pseudomonas aeruginosa after infusion of 1 g and 2 g ceftazidime. Flomoxef showed the highest SBA against methicillin-susceptible Staphylococcus aureus. All cephalosporins had high SBA against gram-negative rods. Cefotaxime had the highest SBA against Klebsiella pneumoniae and Enterobacter cloacae. The SBA against Pseudomonas aeruginosa after 1 g and 2 g doses of ceftazidime was very similar.

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.

Randomised comparison of oral ofloxacin alone with combination of parenteral antibiotics in neutropenic febrile patients

Prompt treatment with empirical antibiotics in neutropenic febrile patients reduces morbidity and mortality. Most patients have been treated with parenteral combination antibiotics, but newer antibiotics with broad-spectrum bactericidal activity have made monotherapy feasible. Ofloxacin, a broad-spectrum fluoroquinolone, has the additional advantage that bactericidal concentrations can be achieved with oral administration. We have compared ofloxacin as an oral single agent with standard parenteral combination antibiotics for the management of neutropenic febrile patients in a prospective, randomised trial. Patients with severe neutropenia (absolute neutrophil count less than or equal to 0.5 x 10(9)/l), fever above 38 degrees C, and ability to take drugs by mouth were eligible for the study. After initial investigations, 60 patients were randomly assigned to oral ofloxacin 400 mg twice daily and 62 to parenteral combination antibiotic therapy (amikacin 15 mg/kg daily, plus, at various times in the trial, carbenicillin, cloxacillin, or piperacillin). Patients were examined 72 h and 7 days after the start of treatment and when neutropenia resolved. 24 (40%) ofloxacin-treated and 26 (42%) combination-treated patients had pyrexia of unknown origin (PUO). In both treatment groups, the treatment success rate was higher for such patients than for those with clinically or microbiologically documented infections (92% vs 67% [p less than 0.05] for ofloxacin; 85% vs 64% for combination). There were no significant differences in success rates of ofloxacin and combination treatment for these subgroups or overall (77% vs 73%). Patients with neutropenia for less than 1 week had better responses to both treatments than patients with longer-lasting neutropenia. There were 4 (7%) deaths in the ofloxacin group and 6 (10%) in the combination group. Both regimens were well tolerated. We conclude that oral single-agent ofloxacin is as effective as parenteral combination antibiotic therapy in neutropenic febrile patients, especially those expected to have short durations of neutropenia.

Antimicrobial activity of Ro 41-1879, a new catechol cephalosporin

The antimicrobial activity and spectrum of Ro 41-1879, a new 7'-catechol substituted cephalosporin, was assessed in a broth microdilution system against 312 clinical isolates. Ro 41-1879 demonstrated a slightly superior spectrum of activity (2- to 32-fold) compared to ceftazidime against Gram-positive cocci, Pseudomonas spp. and Xanthomonas maltophilia. Enterobacteriaceae strains were more susceptible (97% versus 96%) to ceftazidime at less than or equal to 16 micrograms/ml. These results represent a preliminary potency/spectrum analysis for Ro 41-1879 since the screening studies were performed with an in vitro system unlikely to detect the potency contributed by active drug transport (tonB system) into bacterial cells. This new class of cephalosporins shows some therapeutic promise.

Empiric treatment of infection during granulocytopenia

Results from clinical trials conducted over the past 15 years suggest the following: a) Early empiric therapy with broad-spectrum antibiotics directed against Gram-negative bacillary bacteremia is necessary in febrile granulocytopenic cancer patients; b) The level and dynamics of the granulocyte count are extremely important in determining the outcome of bacteremia; c) Most empiric antimicrobial regimens will require therapeutic modifications; these alterations are necessary and contribute to a high overall success rate; d) Only microbiologically documented infections and especially bacteremias are useful for comparison of initial response to antimicrobial regimens; e) The response rate of Gram-negative bacillary bacteremia is clearly influenced by the susceptibility of the causative pathogen to the beta-lactam component of the empiric regimen; emergence of resistance to some beta-lactam antibiotics is quite common and necessitates successive modifications of empiric regimens with time; f) The combination of an anti-pseudomonal beta-lactam with an aminoglycoside is recommended as the standard for empiric therapy in febrile granulocytopenic cancer patients, especially in those with severe and persistent granulocytopenia who are suspected of having Gram-negative bacillary bacteremia; less neutropenic and/or asymptomatic patients may do well with monotherapy; g) Gram-positive pathogens have become a common cause of bacteremia in granulocytopenic cancer patients; the response rate to empiric regimens may be suboptimal but the associated mortality is low; h) Patients with severe granulocytopenia and protracted fever whose blood cultures remain negative are at high risk for contracting fungal infections; in these patients, empiric antifungal agents are probably indicated.

Crossover assessment of serum bactericidal activity and pharmacokinetics of five broad-spectrum cephalosporins in the elderly

To better define the pharmacokinetics and serum bactericidal activity (SBA) of the expanded-spectrum cephalosporins in the elderly, we administered single 2-g intravenous infusions of cefoperazone, cefotaxime, ceftriaxone, ceftazidime, and ceftizoxime to six healthy volunteers over the age of 65 years. Serum was collected over 24 h, and concentrations were determined by high-performance liquid chromatography; pharmacokinetic parameters were determined for each drug. SBA was measured against representative strains of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Enterobacter aerogenes, and Pseudomonas aeruginosa. All agents tested had excellent SBAs against E. coli and K. pneumoniae, often for a longer duration than would be expected on the basis of conventional dosing regimens. Ceftazidime had the greatest SBA against E. aerogenes and was the only agent with a substantial SBA against P. aeruginosa. Although ceftizoxime had the greatest SBA against S. aureus, none of these cephalosporins had substantial antistaphylococcal SBAs. Pharmacokinetic analysis revealed that cefoperazone and ceftriaxone had markedly different concentration-time profiles in the elderly volunteers than would have been expected on the basis of existing data from younger volunteers. For older patients, dosing guidelines for these two agents may need to be altered.

Three-step empiric treatment for severely neutropenic patients with fever: ceftazidime--vancomycin--amphotericin B

In a prospective study 50 febrile episodes in severely neutropenic patients (neutrophils less than 500/mm3) were empirically treated with ceftazidime monotherapy. If no response was seen after 48 h, vancomycin was added. After another 72 h period, patients with persisting fever additionally received amphotericin B. In 29 episodes (58%) patients became afebrile with ceftazidime monotherapy. Another seven patients (14%) responded to the addition of vancomycin and five patients (10%) needed amphotericin B to become afebrile. A success of the study drugs without modification was seen in 40 episodes (80%), success with modification in three episodes (6%) and failure in six episodes (12%). One patient died of myocardial infarction. No other death occurred during the two-week observation period after entering the study. Though there were two gram-negative isolates resistant to ceftazidime, these patients were successfully treated with modification. It is concluded that the response-adapted additive sequence of ceftazidime, vancomycin and amphotericin B is an effective approach towards febrile episodes in severely neutropenic patients.

In vitro activity of Ro 23-9424, ceftazidime, and eight other newer beta-lactams against 100 gram-positive blood culture isolates

One hundred Gram-positive bacteremia organisms from five important genus groups were tested against 10 newer beta-lactams. Ceftazidime was significantly less active (50% of strains at less than or equal to 8 micrograms/ml) compared to other cephalosporins. The penems (FCE-22101 and HRE-664) and imipenem were each superior to the cephalosporins with 92-93% inhibition of strains. A novel fused co-drug of fleroxacin and desacetyl-cefotaxime, Ro 23-9424, was 100% effective against these Gram-positive pathogens at less than or equal to 8 micrograms/ml. Several of these compounds should receive consideration for clinical trials for empiric therapy among neutropenic patient infections where Gram-positive pathogens may be more prevalent.

Cefoperazone plus tobramycin versus ticarcillin plus tobramycin in febrile granulocytopenic cancer patients

Cefoperazone plus tobramycin was compared in a prospective, randomized trial with our standard regimen of ticarcillin plus tobramycin as empiric therapy of fever in granulocytopenic patients with cancer. Patients who received cefoperazone were also given vitamin K (5 mg orally twice a week). Of 39 microbiologically and clinically documented infections treated with ticarcillin plus tobramycin, 28 (72 percent) showed improvement. Of 27 microbiologically and clinically documented infections treated with cefoperazone plus tobramycin, 21 (78 percent) showed improvement. The overall response rates were similar (40 of 53, or 74 percent, for ticarcillin plus tobramycin versus 38 of 48, or 79 percent for cefoperazone plus tobramycin). There was no difference in response between groups according to site of infection. Serious side effects were minimal with both regimens. There were no enterococcal superinfections in patients receiving cefoperazone. These results suggest that the overall efficacy and toxicity of study regimens are similar.

Cefoperazone in the treatment of infections in cancer patients

Cefoperazone appears to be one of the cephalosporins with the most promise in granulocytopenic patients, regardless of whether it is used in combination or as monotherapy. It has the broad spectrum of antimicrobial activity necessary to inhibit the organisms commonly encountered in patients with cancer, as well as the ability to achieve high serum levels for sustained periods of time. Administration of cefoperazone should provide effective therapy in the overall management of most infections encountered in patients with neoplastic diseases.

Serum bactericidal test

The serum bactericidal test represents one of the few in vitro tests performed in the clinical microbiology laboratory that combines the interaction of the pathogen, the antimicrobial agent, and the patient. Although the use of such a test antedates the antimicrobial era, its performance, results, and interpretation have been subject to question and controversy. Much of the confusion concerning the serum bactericidal test can be avoided by an understanding of the various factors which influence bactericidal testing. In addition, the methodologic aspects of the serum bactericidal test have recently been addressed and should place this test on firmer ground. New information on the clinical utility of this test is becoming available; additional data are needed to establish more clearly the usefulness of the serum bactericidal test in specific infections. Such clinical trials from multiple centers will enable firmer recommendations for the future use of the serum bactericidal test.

A randomized trial comparing ceftazidime alone with combination antibiotic therapy in cancer patients with fever and neutropenia

To assess the efficacy of single-agent therapy relative to standard combination antibiotic therapy for the initial management of fever and neutropenia in cancer patients, we conducted a randomized trial comparing ceftazidime alone with a combination of cephalothin, gentamicin, and carbenicillin. Of 550 evaluable episodes of fever and neutropenia, 282 were treated with ceftazidime alone and 268 with the combination. All episodes were evaluated for responses at 72 hours after the start of treatment and at resolution of the neutropenia. Of the patients with unexplained fever who were given ceftazidime alone, 99 percent were alive at 72 hours and 98 percent were alive when the neutropenia resolved, as compared with 100 percent and 98 percent, respectively, of those given combination therapy. Of the patients with documented infection who were given ceftazidime alone, 98 percent were alive at 72 hours and 89 percent when the neutropenia resolved, as compared with 98 percent and 91 percent, respectively, of those given combination therapy. The majority of episodes of documented infection in both treatment groups necessitated additional antimicrobial treatment or other modifications of the initial regimen, as compared with only 22 percent of the episodes of unexplained fever. We conclude that initial single-agent therapy with certain beta-lactam antibiotics is a safe alternative to standard combination antibiotic therapy, although patients with documented infection or protracted neutropenia are likely to require additional or modified treatment.

Serum bactericidal activity and killing rate for volunteers receiving imipenem, imipenem plus amikacin, and ceftazidime plus amikacin against Pseudomonas aeruginosa

Serum bactericidal activity against 20 strains of Pseudomonas aeruginosa was studied in 10 volunteers after administration of imipenem (25 mg/kg), imipenem (25 mg/kg) plus amikacin (7.5 mg/kg), and ceftazidime (25 mg/kg) plus amikacin (7.5 mg/kg). Eight strains were susceptible and 12 were resistant to ticarcillin. Serum levels were measured microbiologically after 30 and 60 min and were, respectively, 97 and 46 micrograms/ml for imipenem given alone and 79 and 45 micrograms/ml for imipenem given with amikacin. Despite the very large dose of imipenem used, imipenem and imipenem plus amikacin appeared slightly less active than ceftazidime plus amikacin (P less than or equal to 0.1; Wilcoxon matched-pairs test), with respective median titers at 30 min of 1:128, 1:128, and 1:256 against ticarcillin-susceptible strains and 1:32, 1:32, and 1:64 against ticarcillin-resistant strains; however, more than 90% of the serum determinations, regardless of the regimen, had a serum bactericidal activity greater than or equal to 1:8. Amikacin significantly increased the rate of killing in serum of P. aeruginosa by imipenem. Imipenem plus amikacin appeared as effective as ceftazidime plus amikacin in reducing the viable counts of P. aeruginosa after 24 h of incubation.

Serum bactericidal activity of two newer quinolones against Salmonella typhi compared with standard therapeutic regimens

The bactericidal activity of two newer quinolones, ciprofloxacin and ofloxacin, against eight strains of Salmonella typhi was examined by the serum dilution test and studies of bacterial killing kinetics in human serum, and compared to standard regimens. Bactericidal titers for ciprofloxacin ranged from 1:388 to 1:119 two hours and from 1:119 to 1:57 six hours after volunteers received an oral dose of 500 mg. The respective titers obtained after a 200 mg oral dose of ofloxacin were somewhat lower, but still exceeded 1:16 in all instances. Studies of bacterial killing kinetics demonstrated a rapid bactericidal action of both drugs against all strains tested. Compared to the classical anti-typhoid agents chloramphenicol, cotrimoxazole and amoxicillin, the new quinolones showed both markedly higher bactericidal titers and more rapid killing of Salmonella typhi in human serum.

Serum bactericidal activity of mezlocillin, ceftazidime, mezlocillin/ceftazidime and mezlocillin/amikacin against Klebsiella pneumoniae and Pseudomonas aeruginosa

Sera of volunteers receiving 1 g mezlocillin, 5 g mezlocillin, 1 g ceftazidime, 3 g ceftazidime, 1 g mezlocillin plus 1 g ceftazidime, and 1 g mezlocillin plus 500 mg amikacin, respectively, were evaluated for bactericidal activity against clinical isolates of Klebsiella pneumoniae and Pseudomonas aeruginosa. The titers of bactericidal activity against Klebsiella pneumoniae in serum from subjects receiving ceftazidime were higher than with other regimens both one and six hours after administration. Peak titers of bactericidal activity greater than or equal to 1:8 were also achieved more often against Pseudomonas aeruginosa in sera from subjects receiving ceftazidime than with other regimens. Killing studies confirmed these results. Although the checkerboard technique indicated synergism with the combination mezlocillin plus amikacin in vitro, this was not confirmed in vivo. Single drug therapy with ceftazidime was superior to the tested combinations.

Comparison of the serum bactericidal activity of ceftriaxone/piperacillin and ceftriaxone/netilmicin

The serum bactericidal activities of ceftriaxone, netilmicin, piperacillin and the combinations of ceftriaxone with each of the two other antibiotics were compared 1, 4 and 24 h after i.v. infusion in six volunteers. One hundred and one clinical isolates were used, including Staphylococcus aureus, Pseudomonas aeruginosa and various Enterobacteriaceae. The highest bactericidal titers were found against the Enterobacteriaceae, geometric means of 1:741 and 1:851 being obtained for ceftriaxone/netilmicin and ceftriaxone/piperacillin respectively. Against Staphylococcus aureus the geometric mean bactericidal titers of ceftriaxone/piperacillin (1:105) were markedly higher than ceftriaxone/netilmicin (1:35). Low bactericidal activity was exhibited by all drugs and combinations tested against Pseudomonas aeruginosa; a geometric mean bactericidal titer of 1:4.6 was achieved. The serum bactericidal activity of the double beta-lactam combinations was found to be at least equal to that of the combination containing a cephalosporin and an aminoglycoside.

Serum bactericidal activity of ceftazidime increased by netilmicin

Cephalosporins are often used in combination with aminoglycoside antibiotics in the treatment of gram-negative infections. Although ceftazidime possesses activity against gram-negative bacteria, especially against Pseudomonas, combined use with aminoglycosides is useful. In this study, 12 healthy volunteers (6 men, 6 women; mean age 21.5 yr) received a single dose of ceftazidime 1 g iv and one week later ceftazidime 1 g iv with netilmicin 100 mg iv. Both antibiotics were infused over five minutes. Concentrations of ceftazidime were determined by high performance liquid chromatography. Serum bactericidal activity (SBA) was evaluated against seven microorganisms isolated from clinical specimens. The mean peak serum level of ceftazidime was 113.4 micrograms/ml. At eight hours, we observed a concentration of 2.6 micrograms/ml. The total clearance was 126 ml/min, while the renal clearance was 100 ml/min. Ceftazidime exhibited a half-life of 1.9 hours. Up to ten hours, the SBA of ceftazidime against Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, and Salmonella typhi was greater than 1:8 in more than 90 percent of samples. At one hour, ceftazidime exhibited a SBA of 1:4 for Staphylococcus aureus, and 1:16 for Pseudomonas aeruginosa. With the addition of netilmicin, median SBA against Staph. aureus and P. aeruginosa were 1:32 and 1:64, respectively, at one hour. Netilmicin enhanced the SBA of ceftazidime. The combination was not effective against Streptococcus faecalis.

Antimicrobial activity, pharmacokinetics, therapeutic indications and adverse reactions of ceftazidime

Ceftazidime is an aminothiazolyl cephalosporin with potent activity against gram-negative bacteria including multiresistant strains of Pseudomonas aeruginosa. It has limited activity against gram-negative anaerobes, is less active against some gram-positive cocci than other newer beta-lactam compounds and is inactive against Streptococcus faecalis and methicillin-resistant Staphylococcus aureus. Ceftazidime is stable against common plasmid and chromosomally mediated beta-lactamase produced by Enterobacteriaceae and Pseudomonas sp. Its pharmacokinetic properties are similar to those of moxalactam and ceftizoxime, and it has a half-life of 1.9 hours. Excretion is by glomerular filtration. It is not metabolized. Ceftazidime penetrates into most body tissue and fluids, including cerebrospinal fluid, and produces therapeutic levels against most of the pathogenic gram-negative bacteria, including P. aeruginosa. Ceftazidime accumulates during renal failure, but is removed by hemodialysis and peritoneal dialysis. As a single agent it has been shown effectively to treat meningitis; urinary tract infections; gram-negative pneumonia; bone, joint and skin infections; and obstetric and gynecologic infections due to susceptible organisms. When combined with an agent that is effective against gram-positive organisms, it is also beneficial in the treatment of infections in seriously ill neonates. Different investigators have used ceftazidime alone or in combination with other agents in the successful treatment of infections in immunosuppressed patients. Adverse reactions have been few and are mostly reversible laboratory findings. The effects of ceftazidime on prothrombin synthesis and platelet function have been minimal, and no drug-induced clinical bleeding has been reported.

Can the third-generation cephalosporins eliminate the need for antimicrobial combinations?

Antimicrobial combinations have been widely utilized since the beginning of the chemotherapeutic era. This is true despite the fact that the use of such combinations has a number of potential disadvantages, including (1) antibiotic antagonism; (2) an increased incidence of toxicity; (3) the emergence of multi-resistant organisms; (4) promotion of a false sense of security; and (5) increased expense. The reasons generally given for the use of such combinations include (1) antimicrobial synergism, (2) suppression of antimicrobial resistance, (3) decreased toxicity, and (4) broader coverage. Although there are clearly some situations in which synergistic combinations have been shown to be useful (such as in the treatment of enterococcal endocarditis and severe Pseudomonas infections), the use of combination therapy to reduce the emergence of resistance (excluding the treatment of mycobacterial infections and of infections in which rifampin is used) or to reduce toxicity has not met with widespread success. Indeed, most combinations are used simply to broaden the spectrum of antimicrobial coverage. The development of new penicillins and cephalosporins with broader spectra of activity has raised the distinct possibility that these drugs could be used as single agents for the treatment of most serious infections. Although comparative studies performed to date suggest that the new broad-spectrum penicillins and cephalosporins may be useful as single agents in the treatment of infections in a variety of clinical situations in which combinations are now commonly employed, additional studies enrolling greater numbers of patients are necessary to determine whether these agents can replace combination therapy. The use of single-drug therapy in the management of febrile episodes and documented infections in neutropenic patients remains problematic because of the greater likelihood of infections with organisms such as Pseudomonas aeruginosa, in which case combination therapy is often required. Earlier studies have clearly documented that combinations of antibiotics that are synergistic are more effective in treating bacteremias and other serious infections in neutropenic patients than are combinations that have failed to demonstrate synergism. Because of the increased activity of some of the newer drugs, such as ceftazidime, against P. aeruginosa it is possible that such agents could be used as monotherapy for patients with severe neutropenia. This possibility is an attractive one, but it should be studied carefully to make certain that it will not be associated with significant failure due to the emergence of resistant organisms.

Ceftazidime. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Ceftazidime is a new 'third generation' cephalosporin administered intravenously or intramuscularly. Similarly to other third generation cephalosporins it has a broad spectrum of in vitro activity against Gram-positive and Gram-negative aerobic bacteria, is particularly active against Enterobacteriaceae (including beta-lactamase-positive strains) and is resistant to hydrolysis by most beta-lactamases. Importantly, in vitro ceftazidime is presently the most active cephalosporin available against Pseudomonas aeruginosa, but it is less active against Staphylococcus aureus than first and second generation cephalosporins. Only larger comparative trials are likely to discern any statistically significant differences in clinical efficacy which may exist between ceftazidime and other antibiotics, but ceftazidime appears to be similar in efficacy to 'standard' comparative drugs in lower respiratory tract infections and complicated and/or chronic urinary tract infections among debilitated or hospitalised patients. Thus, in patients having Gram-negative infections at these sites and in whom the potential toxicity of the aminoglycosides is a concern, ceftazidime may be a valuable alternative in that it apparently lacks serious side effects and does not require routine drug plasma concentration monitoring. In fibrocystic patients having acute respiratory tract infections, ceftazidime is highly effective at both reducing symptoms of infection and temporarily reducing the sputum counts of Pseudomonas species. However, in these patients resistance to ceftazidime may develop, as seen with other beta-lactam antibiotics. In the treatment of fever of unknown origin or documented infections in immunocompromised adults and children, ceftazidime appears to be similar in efficacy to various 2- or 3-drug combinations. Nevertheless, the coadministration of an antibiotic having greater efficacy against Gram-positive bacteria should be considered in immunocompromised patients. Results from a small number of comparative trials suggest that ceftazidime may be as effective as the aminoglycosides in intra-abdominal, obstetric and gynaecological, and skin and soft tissue infections. However, further clinical experience, particularly a few well designed comparative studies, is needed to clarify the comparative efficacy in these conditions as well as in septicaemia/bacteraemia, meningitis, and bone and joint infections.

Single-drug versus combination empirical therapy for gram-negative bacillary infections in febrile cancer patients with and without granulocytopenia

Empirical therapy with cefoperazone was compared with cefoperazone plus amikacin in granulocytopenic and nongranulocytopenic febrile patients. In nonneutropenic patients the overall response rate to cefoperazone was 88%; 10 of 12 gram-negative bacteremic patients were cured. Cefoperazone plus amikacin resulted in an 88% overall response rate and cured 14 of 15 patients with bacteremia. In neutropenic patients the overall response rate was 77% with cefoperazone alone and 73% with cefoperazone plus amikacin; the cure rates for gram-negative bacteremias were 8 of 11 and 6 of 12 patients, respectively. Our findings support the concept of single-drug empirical therapy with cefoperazone in febrile cancer patients, whether granulocytopenic or not, especially when gram-negative bacteremias are predominantly caused by Escherichia coli or Klebsiella species. The issue of Pseudomonas spp. and other more resistant pathogens needs further assessment with a larger number of patients.

Early synergistic interactions between amikacin and six beta-lactam antibiotics against multiply resistant members of the family Enterobacteriaceae

An in vitro comparison of the early synergistic interaction between amikacin and each of six beta-lactam antibiotics was made by using time-kill curves against 48 multiply resistant members of the family Enterobacteriaceae. Overall, these six combinations demonstrated early synergism (greater than or equal to 2 logs of increased kill after 7 h of incubation) against the 48 strains on 74% (range, 67 to 85%) of occasions; cefotaxime-amikacin and piperacillin-amikacin were the most efficacious combinations. Antagonism was not observed with any of the combinations against any of the 48 Enterobacteriaceae strains tested.

Bactericidal activity of ceftazidime in serum compared with that of ticarcillin combined with amikacin

We compared the bactericidal activity of serum attained 1 and 6 h after the termination of infusions of either ceftazidime (2 g) or ticarcillin plus amikacin (5 g and 7.5 mg/kg, respectively) in 6 volunteers against a panel of the most common pathogens found in the blood of febrile granulocytopenic cancer patients. Ceftazidime consistently produced significantly higher serum bactericidal titers at both 1 and 6 h against all species of gram-negative bacilli. Its performance against Pseudomonas aeruginosa was especially impressive. The geometric mean titer against this organism was 1:41 at 1 h, contrasted with 1:12 for ticarcillin plus amikacin (P = 0.025). However, for Staphylococcus aureus, the geometric mean serum bactericidal titer of ceftazidime was 1:3.6 at 1 h and undetectable at 6 h. Ceftazidime shows promise as single-agent therapy for serious gram-negative bacillary infections. Whether this promise is fulfilled and whether the observed antistaphylococcal activity is adequate for empiric therapy in infected granulocytopenic patients need further investigation.

Changing patterns of resistance to new beta-lactam antibiotics. In vitro efficacy of cefoperazone against bacterial pathogens

No evidence for significant increase in resistance to cefoperazone was detected in susceptibility test surveillance programs or in the literature through 1983, but rare endemic resistance to cefoperazone and some other newer beta-lactams was found. Medical centers contemplating the use of a third-generation drug for cost-containment should be aware of the susceptibility of isolates in their hospitals, and the drug's ability to withstand beta-lactamase hydrolysis by local pathogens. The possible dangers of inducible cephalosporins in certain Enterobacteriaceae and strains of Pseudomonas aeruginosa are discussed in the light of the physical and chemical characteristics of the newer antimicrobial agents. Criteria for judging the values of investigational beta-lactams are presented. These focus on the interaction of antimicrobial agents with host defense mechanisms and circulating blood elements.

Treatment of gram-negative bacillary septicemia with cefoperazone

Cefoperazone, a new broad-spectrum cephalosporin, was administered by continuous infusion or intermittent injection to 20 and 25 patients respectively with gram-negative bacillary septicemia most of whom had severe underlying disease. No difference was observed in the clinical response of the two groups. The overall rate of favourable response was 76%. Of the 40 non-neutropenic patients treated three died of infection despite sensitivity of the organism, three improved temporarily and three died as the result of superinfection. Three of the five neutropenic patients treated failed to respond to cefoperazone therapy, despite adequate serum bactericidal activity. Tolerance to cefoperazone was satisfactory. Emergence of cefoperazone-resistant strains leading to relapse or superinfection was not a major cause of failure.

Value of serum tests in combined drug therapy of endocarditis

Two in vitro tests, the serum killing level and the serum bactericidal rate assays, were evaluated for correlation with therapeutic efficacy in the rabbit model of Staphylococcus aureus endocarditis. Animals were treated with nafcillin alone and in combination with tobramycin or gentamicin. Both were effective therapies, but rapidity of vegetation sterilization by the single and combined regimens was shown by the serum bactericidal rate assay but not the serum killing level assay. As a direct measure of bactericidal activity in serum during therapy, the serum bactericidal rate assay may be a clinically useful supplemental test for providing information that the serum killing level assay cannot.