In vitro and in vivo antibacterial properties of FK 027, a new orally active cephem antibiotic

The Chemical Relationship Among Beta-Lactam Antibiotics and Potential Impacts on Reactivity and Decomposition

Beta-lactam antibiotics remain one of the most commonly prescribed drug classes, but they are limited by their propensity to cause hypersensitivity reactions (e.g., from allergy to anaphylaxis) as well as by the emergence of bacteria with a myriad of resistance mechanisms such as β-lactamases. While development efforts continue to focus on overcoming resistance, there are ongoing concerns regarding cross-contamination of β-lactams during manufacturing and compounding of these drugs. Additionally, there is a need to reduce levels of drugs such as β-lactam antibiotics in waste-water to mitigate the risk of environmental exposure. To help address future development of effective remediation chemistries and processes, it is desired to better understand the structural relationship among the most common β-lactams. This study includes the creation of a class-wide structural ordering of the entire β-lactam series, including both United States Food and Drug Association (US-FDA)-approved drugs and experimental therapies. The result is a structural relational map: the “Lactamome,” which positions each substance according to architecture and chemical end-group. We utilized a novel method to compare the structural relationships of β-lactam antibiotics among the radial cladogram and describe the positioning with respect to efficacy, resistance to hydrolysis, reported hypersensitivity, and Woodward height. The resulting classification scheme may help with the development of broad-spectrum treatments that reduce the risk of occupational exposure and negative environmental impacts, assist practitioners with avoiding adverse patient reactions, and help direct future drug research.

Automatic phylogenetic classification of bacterial beta-lactamase sequences including structural and antibiotic substrate preference information

Beta lactams comprise the largest and still most effective group of antibiotics, but bacteria can gain resistance through different beta lactamases that can degrade these antibiotics. We developed a user friendly tree building web server that allows users to assign beta lactamase sequences to their respective molecular classes and subclasses. Further clinically relevant information includes if the gene is typically chromosomal or transferable through plasmids as well as listing the antibiotics which the most closely related reference sequences are known to target and cause resistance against. This web server can automatically build three phylogenetic trees: the first tree with closely related sequences from a Tachyon search against the NCBI nr database, the second tree with curated reference beta lactamase sequences, and the third tree built specifically from substrate binding pocket residues of the curated reference beta lactamase sequences. We show that the latter is better suited to recover antibiotic substrate assignments through nearest neighbor annotation transfer. The users can also choose to build a structural model for the query sequence and view the binding pocket residues of their query relative to other beta lactamases in the sequence alignment as well as in the 3D structure relative to bound antibiotics. This web server is freely available at http://blac.bii.a-star.edu.sg/.

Competition of various beta-lactam antibiotics for the major penicillin-binding proteins of Helicobacter pylori: antibacterial activity and effects on bacterial morphology

The penicillin-binding proteins (PBPs) of helical (log-phase) Helicobacter pylori ATCC 43579 were identified by using biotinylated ampicillin. The major PBPs had apparent molecular masses of 47, 60, 63, and 66 kDa; an additional minor PBP of 95 to 100 kDa was also detected. The relative affinities of various beta-lactams for these PBPs were tested by competitive-binding assays. Only PBP63 appeared to be significantly bound to each of the competing antibiotics, whereas PBP66 strongly bound mezlocillin, oxacillin, amoxicillin, and ceftriaxone. Whereas most of the beta-lactams significantly bound two or more PBPs, aztreonam specifically targeted PBP63. The influence of sub-MICs of these beta-lactams on the morphologies of log-phase H. pylori was observed at both the phase-contrast and transmission electron microscopy levels. Each of the eight beta-lactams examined induced blebbing and sphere formation, whereas aztreonam was the only antibiotic studied which induced pronounced filamentation in H. pylori. Finally, studies comparing the PBPs of helical (log-phase) cultures with those of coccoid (7-, 14-, and 21-day-old) cultures of H. pylori revealed that the major PBPs at 60 and 63 kDa seen in the helical form were almost undetectable in the coccoid forms, whereas PBP66 remained the major PBP in the coccoid forms, although somewhat reduced in level compared to the helical form. PBP47 was present in both forms at approximately equal concentrations. These studies thus identified the major PBPs in both helical and coccoid forms of H. pylori and compared the relative affinities of seven different beta-lactams for the PBPs in the helical forms and their effects on bacterial morphology.

Cefaclor: a contemporary look at susceptibility of key pathogens from around the globe

The orally administered cephalosporin antibiotic, cefaclor, has been available for clinical use in many countries since 1979. Because widespread antibiotic use is often cited as a factor in the emergence of bacterial resistance to antibiotics, we sought to determine the degrees of resistance to cefaclor expressed by key pathogens recently isolated in 10 countries widely distributed around the world. Using the E-test, minimal inhibitory concentrations (MIC) were determined for cefaclor and several comparator antibiotics against approximately 700 fresh clinical isolates of each of six bacterial species. The results demonstrated that > 90% of Haemophilus influenzae (beta-lactamase producing and non-producing), Haemophilus parainfluenzae (beta-lactamase producing and non-producing), Moraxella catarrhalis (> 90% beta-lactamase producing), and methicillin-susceptible Staphylococcus aureus, and 85% of Escherichia coli were susceptible to cefaclor at the NCCLS interpretive breakpoints. MIC distributions showed that there has been no change in the activity of cefaclor against penicillin-susceptible strains of Streptococcus pneumoniae since 1977.

Pharmacokinetics of cefixime in children with urinary tract infections after a single oral dose

The pharmacokinetics of cefixime, a third-generation broad-spectrum cephalosporin, were determined following administration of a 8 mg/kg single oral dose of cefixime suspension to six children with urinary tract infections, ages from 6 to 13 years and weights from 17 to 60 kg. Blood samples for determination of plasma cefixime concentrations were obtained for up to 12 hr and complete urine collections were obtained for urinary excretion of unchanged parent drug for up to 24 hr after administration. Plasma and urine concentrations of cefixime were determined using a reversed phase HPLC assay and pertinent pharmacokinetic parameters were estimated by model-independent standard methods. Mean peak plasma concentration was 4.04 micrograms/ml and was reached after 3.2 hr. The mean area under the plasma concentration-time curve was 33.07 micrograms.hr/ml and the mean elimination half-life was 3.91 hr. The mean apparent total clearance was 4.74 ml/min./kg and about 15% of the dose administered was recovered unchanged in urine. In conclusion, the estimated pharmacokinetic values of cefixime were comparable to those observed in healthy adult subjects based on equivalent mg/ kg doses. Plasma and urine concentrations of the drug were well above the reported minimal plasma and urinary concentrations for most common urinary tract pathogens for up to 12 and 24 hr after administration, respectively.

In vitro and in vivo antibacterial activities of S-1090, a new oral cephalosporin

S-1090, a new oral cephalosporin, was active against selected gram-negative bacteria and methicillin-susceptible clinical isolates of Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus warneri, against which it had excellent activity. S-1090 was the most active compound against Streptococcus pyogenes and Streptococcus agalactiae among the agents compared. The in vivo efficacy of S-1090 against systemic and urinary and respiratory tract infections caused by gram-positive and -negative bacteria was superior to that expected from the in vitro and in vivo activities of the agents against which it was compared.

In vitro antibacterial activity and beta-lactamase stability of SY5555, a new oral penem antibiotic

The antibacterial activity of SY5555, a new oral penem antibiotic, was compared with those of cefaclor, cefixime, and cefteram. SY5555 was more active than the comparison agents against methicillin-susceptible Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Enterococcus faecalis, Citrobacter freundii, Enterobacter cloacae, Morganella morganii, Acinetobacter calcoaceticus, Clostridium spp., and Bacteroides fragilis. Against Providencia spp., Proteus spp., and Haemophilus influenzae, SY5555 was less active than cefixime or cefteram. SY5555 was inactive against methicillin-resistant S. aureus. Enterococcus faecium, Serratia marcescens, Pseudomonas aeruginosa, and Xanthomonas maltophilia, as were the comparison agents. The bactericidal activities of SY5555, cefixime, and cefteram were at or slightly greater than the MICs for clinical isolates of Escherichia coli and Klebsiella pneumoniae. SY5555 was not hydrolyzed by various types of beta-lactamases. However, SY5555 and the comparison agents were hydrolyzed by X. maltophilia (L-1) and P. aeruginosa/pMS354 beta-lactamases, two Bush group 3 beta-lactamases, SY5555 showed a high affinity, as did cefixime and cefteram, for cephalosporinases from C. freundii GN7391 and E. cloacae GN7471 strains. These results suggest that SY5555 may be more specific than existing beta-lactam antibiotics.

Interpretive accuracy of the disk diffusion method for testing newer orally administered cephalosporins against Morganella morganii

Eight newer orally administered cephems (cefdinir, cefetamet, cefixime, cefpodoxime, cefprozil, ceftibuten, cefuroxime, and loracarbef) were tested against 100 clinical strains of Morganella morganii to determine the extent of serious interpretive very major (false-susceptible) errors when current criteria for the disk diffusion test are applied. Agar dilution MICs and disk diffusion tests were performed as recommended by the National Committee for Clinical Laboratory Standards (Villanova, Pa.) (NCCLS), and the methods were compared by regression analysis using the method of least squares and by error rate bounding. The following results are listed in the order of increasing error rates: cefdinir, loracarbef, and cefprozil, < or = 1% very major error; ceftibuten, 8% minor errors; cefuroxime, 21% minor errors; cefixime, cefpodoxime, and cefetamet, very major errors of 15, 24, and 36%, respectively. M. morganii produces unacceptable rates of test error with cefuroxime, cefixime, cefpodoxime, and cefetamet. The latter two cephalosporins currently have NCCLS table footnote warnings covering the problem observed with this organism. The inclusion of cefuroxime and cefixime in the NCCLS table footnote is strongly recommended.

Antibacterial activity of the investigational oral and parenteral cephalosporin BK-218

BK-218 is a novel cephalosporin with a dual route of administration and spectrum of activity most similar to that of second-generation cephalosporins. BK-218 was active against Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis but strains resistant to penicillins had higher MICs. BK-218 had greater activity (8-fold) than cefuroxime or cefaclor against oxacillin-susceptible Staphylococcus spp. Moderate BK-218 activity was observed against Neisseria gonorrhoeae and commonly isolated Enterobacteriaceae such as Escherichia coli (MIC90, 1 mg/l), Klebsiella spp. (MIC90, 2 mg/l), and Proteus mirabilis (MIC90, 2 mg/l). The following organisms were generally BK-218-resistant (MIC90, greater than 16 mg/l): Bacteroides fragilis, Pseudomonas spp., Acinetobacter spp., Xanthomonas maltophilia, Citrobacter spp., Enterobacter spp., indole-positive Proteus, Serratia spp., enterococci and oxacillin-resistant staphylococci.

Relationship between renal function and disposition of oral cefixime

The pharmacokinetics of cefixime following a single oral dose of 200 mg have been investigated in 6 normal subjects and in 22 patients with various degrees of renal insufficiency. Serum and urine samples were collected between 0 and 72 h and were subjected to two methods of analysis: bioassay and HPLC. There was a linear relationship between the two sets of results from 228 samples. This result suggests that none of the metabolites, which may accumulate in uraemic patients, has antibacterial activity. In normal subjects, the peak serum level (Cmax) was 2.50 micrograms.ml-1 at 2.83 h (tmax); the apparent elimination half-life (t1/2) was 3.73 h; the apparent total body clearance (CL.f-1) was 154 ml.min-1, the mean renal clearance (CLR) was 39.1 ml.min-1 and the apparent fraction of the dose recovered in 24 h urine was 0.22. In uraemic patients, Cmax and tmax were slightly increased and t1/2 was increased to 12-14 h in patients with an endogenous creatinine clearance below 20 ml.min-1. The apparent volume of distribution was decreased. Apparent total and renal clearances were lower in proportion to the degree of renal insufficiency. Linear relationships were found between CL/f, CLR and creatinine clearance (CLCR). The findings suggest that the dose of cefixime needs to be reduced only in patients with severe renal failure.

Antimicrobial activity and spectrum of ceftibuten (7432-S, SCH 39720)--a review of United States and Canadian results

Preliminary in vitro studies of ceftibuten in the United States and Canada have demonstrated a potent activity against enteric bacilli (greater than 90% of routine clinical isolates), Haemophilus influenzae, Moraxella catarrhalis, Neisseria spp., most B-hemolytic streptocci, and Streptococcus pneumoniae. Ceftibuten was demonstrated to be bactericidal, minimally influenced by high inocula, beta-lactamase stable, an inhibitor of type Ia beta-lactamase, and potentially usable against some Enterobacteriaceae strains capable of destroying other newer cephalosporins (ceftazidime and cefixime). In vitro test methods have been standardized, and preliminary quality control guidelines have been proposed for clinical trials. The ceftibuten spectrum seems best suited for therapy of urinary tract, respiratory, and genital tract infections as an alternative to older oral cephalosporins, recently marketed esters (cefuroxime axetil), and cefixime.

Activity of cefixime against Helicobacter pylori and affinities for the penicillin-binding proteins

Cefixime induced the formation of rounded cells from the spiral bacillary form of Helicobacter pylori at the MIC or less. Three main penicillin-binding proteins, called A, B and C, were separated from H. pylori. Cefixime had the strongest affinity to penicillin-binding protein B. The binding of cefixime to this protein may induce the formation of rounded H. pylori cells.

Antimicrobial activity and beta-lactamase stability of BMY-28232, parent compound of an oral cephalosporin

BMY-28232, an aminothiazolyl imino methoxy cephalosporin which is available as an orally absorbed acetoxyethyl ester, inhibited strains of methicillin-susceptible Staphylococcus aureus, hemolytic streptococci, Streptococcus pneumoniae, Escherichia coli, Klebsiella species, and many strains of Proteus and Providencia stuartii at concentrations less than 1 microgram/ml, including isolates resistant to cephalexin and cefaclor. It had activity similar to that of cefixime, but was more active against methicillin-susceptible staphylococci. BMY-28232 was a poor substrate for beta-lactamases but was destroyed by the new TEM-3 enzyme, and had less activity against Enterobacter species, Citrobacter freundii, and Proteus vulgaris isolates. Methicillin-resistant staphylococci, Pseudomonas species, enterococci, Listeria monocytogenes, Corynebacterium jeikeium, Bacteroides fragilus and some strains of Clostridium species were resistant to BMY-28232.

Comparative in vitro activity of cefixime against Haemophilus influenzae isolates, including ampicillin-resistant, non-beta-lactamase-producing isolates, from pediatric patients

The in vitro activity of cefixime was comparatively tested against 232 non-type b and 102 type b isolates of Haemophilus influenzae derived from clinical specimens of pediatric patients, including 10 non-type b strains that did not produce beta-lactamase and demonstrated resistance to ampicillin. Cefixime was active against the ampicillin-susceptible and ampicillin-resistant, beta-lactamase-producing isolates; however, its activity against some non-beta-lactamase-producing, ampicillin-resistant isolates appeared to be limited.

Treatment of sinus empyema in adults. A coordinated Nordic multicenter trial of cefixime vs. cefaclor

In sinus empyema, H. influenzae is the most prevalent pathogen in some subpopulations and in case of therapeutic failure. Cefixime, the first oral cephalosporin of the 3rd generation, is highly potent in vitro against H. influenzae. To study the efficacy and safety of cefixime in adults with acute sinusitis, a coordinated, double-blind multicenter trial was designed for purulent cases, as confirmed by antral aspiration. A total of 364 patients were enrolled in the study with 125 cases randomized to the reference group, assigned to treatment with cefaclor. Evaluation was based on clinical outcome and on antral reaspiration (86% of the cases). No significant differences between the treatment groups were found, as regards short-term or long-term clinical outcome. However, the clinical examination overestimated the therapeutic results. Only 4% of the patients were considered as failures, but the re-aspiration demonstrated remaining suppuration in 14% of all cases (p less than 0.001). Based on re-aspiration, the failure rate among patients with initial growth of pathogens was lower for cefixime (8%) than for cefaclor (20%) (p less than 0.05). Such a difference was not found among patients with growth of H. influenzae. No serious adverse reactions were recorded, but loose stools and diarrhoea were significantly more frequent in the cefixime treatment group. Five patients (2%) in the cefixime treatment group discontinued their treatment due to adverse events.

[Cefixime treatment in different bacterial infections in the ENT region]

The clinical efficacy and tolerance of cefixime were evaluated in an open uncontrolled clinical trial including 37 patients suffering from ENT-infections. The MIC90 values of this new oral cephalosporin against gram-negative pathogens are less than 1 mg/l. The antibacterial activity of cefixime against gram-negative pathogens is stronger than that of other oral cephalosporins. Cefixime was administered for five to twelve days twice daily in a dose of 200 mg. In one patient the treatment with cefixime was discontinued after five days due to perioral dermatitis. In 33 of 36 patients cure or distinct improvement was observed after cefixime treatment, showing a clinical success rate of 91.7%. Causative organisms were isolated in 17 of 37 patients (47.2%). After the cefixime therapy the causative organisms were eradicated in 13 of 17 patients (76.5%). The tolerance of cefixime is comparable with that of other oral cephalosporins.

[Effectiveness and tolerance of cefixime in bacterial infections in the ENT area]

Clinical efficacy and tolerance of cefixime were investigated in an open, uncontrolled trial. 200 mg of cefixime were applied twice daily, duration of therapy was between eight and 14 days (mean value 10.1 days, standard deviation +/- 1.4 days). Ten male patients (mean age 42.7 years) and 19 female patients (mean age 34.4 years) were enrolled. Cure or improvement was observed in all 27 patients evaluable for efficacy of treatment. Bacteriological results based on 15 bacteriologically evaluable patients were: elimination of the initial pathogen 60%, persistence 40%. Unwanted side effects and their incidence among the 29 patients evaluable for tolerance were: diarrhoea eight patients (mild to moderate, limited to three to four days on average), nausea and vomiting one patient, discharge and pruritus one patient.

Cefixime

Cefixime is a new orally active third-generation cephalosporin with a broad spectrum of activity against a variety of both gram-positive and -negative bacteria including many beta-lactamase-producing strains of streptococci, Haemophilus influenzae, Neisseria gonorrhoeae, and the majority of the Enterobacteriaceae. Activity of cefixime against Staphylococcus aureus, enterococci, Listeria monocytogenes, and Pseudomonas spp. is poor. The relatively long elimination half-life of cefixime (approximately 3.0 h) has made possible once- to twice-daily administration with the potential added benefit of improved patient compliance. Clinical trials indicate that cefixime is at least as effective as standard agents in the treatment of genitourinary and upper respiratory tract infections. The incidence of resistant organisms reported during clinical trials with cefixime was low. Adverse reactions observed during clinical trials were relatively uncommon and generally mild and transient in nature. The most significant adverse reactions reported were diarrhea and stool changes occurring in up to 20 percent of patients.

Antimicrobial activity and stability to beta-lactamase of BMY-28271, a new oral cephalosporin ester

BMY-28271, the acetoxyethyl ester of BMY-28232, 7-[(Z)-2-(2-aminothiazol-4-yl)-2-hydroxyiminoacetamido]-3(Z) -propen-1-yl-3- cephem-4-carboxylic acid, is a new oral cephalosporin. BMY-28232 has a widely expanded spectrum with high activity against gram-positive and gram-negative bacteria. BMY-28232 is far more active than cefixime or cefteram against Staphylococcus aureus and Staphylococcus epidermidis. Against gram-negative bacteria, the activity of BMY-28232 was comparable to or somewhat weaker than that of cefixime or cefteram. BMY-28232 was a poor substrate for various beta-lactamases. Orally administered BMY-28271 had a good therapeutic effect on systemic infections with S. aureus and some gram-negative bacteria in mice. Oral BMY-28271 was efficacious against S. aureus Smith infection: the efficacy of BMY-28271 was 80 to 90 times higher than that of cefixime or cefteram.

Single-dose oral cefixime versus amoxicillin plus probenecid for the treatment of uncomplicated gonorrhea in men

In this randomized study, a single 800-mg oral dose of cefixime cured 96 of 97 men with uncomplicated gonococcal urethritis, compared with 44 cures of 46 men who received standard therapy with amoxicillin (3 g) plus probenecid (1 g). Both regimens were ineffective against coexistent infection with Chlamydia trachomatis and Ureaplasma urealyticum. Cefixime was well tolerated, and all side effects were mild and self-limited.

In vitro activities and targets of three cephem antibiotics against Haemophilus influenzae

The antimicrobial activities of cefixime, cefpodoxime, and ceftibuten were determined with 18 ampicillin-susceptible (Amps), 13 ampicillin-resistant beta-lactamase-producing (AmprBLP), and 7 ampicillin-resistant non-beta-lactamase-producing (AmprNBLP) strains of Haemophilus influenzae. An effect of inoculum density on apparent MIC, the bactericidal activity of these agents, and the targets of the three cephems were determined. The MICs of cefixime, cefpodoxime, and ceftibuten for 90% of the Amps and AmprBLP isolates were 0.04, 0.08, and 0.08 microgram/ml, respectively. In contrast, the MICs for 90% of the AmprNBLP strains were 0.96, 1.92, and 7.68 micrograms/ml. No significant inoculum effect was observed for any group of strains comparing inocula of 10(3) and 10(5) CFU, whereas only the AmprNBLP isolates showed a marked effect at an inoculum of 10(6) CFU. Although bactericidal levels were achieved for the Amps and AmprBLP strains, tolerance to cefixime and ceftibuten was observed. The bactericidal activity for the AmprNBLP strains was limited, with cefixime showing the highest activity of the three cephems. Penicillin-binding proteins 2, 4, and 5 revealed high affinity, with 50% inhibitory concentration levels below the MIC for all three cephems, suggesting that these are important targets of these agents in H. influenzae. We conclude that the cephems are highly active in vitro against Amps and AmprBLP strains of H. influenzae, but less so against AmprNBLP isolates.

Cefixime. A review of its antibacterial activity. Pharmacokinetic properties and therapeutic potential

Cefixime, previously designated FK027, FR17027 and CL284635, is an orally active cephalosporin with a broad spectrum of antibacterial activity in vitro. It is particularly active against many Enterobacteriaceae, Haemophilus influenzae. Streptococcus pyogenes, Streptococcus pneumoniae and Branhamella catarrhalis, and is resistant to hydrolysis by many beta-lactamases. Cefixime has little activity against Staphylococcus aureus and is inactive against Pseudomonas aeruginosa. Cefixime is distinguished by its 3-hour elimination half-life which permits twice daily, or in many instances once daily, administration. Comparative trials, though few, indicate that the clinical and bacteriological efficacy of cefixime 200 to 400mg daily administered as a single dose or in 2 divided doses, is comparable with that of multiple daily doses of co-trimoxazole (trimethoprim + sulphamethoxazole) or amoxycillin in acute uncomplicated urinary tract infection, with that of amoxycillin, amoxycillin/clavulanic acid and cefaclor in acute lower respiratory tract infections, and with that of amoxycillin and cefroxidine in adult patients with acute tonsillitis or pharyngitis. Several comparative trials in children with acute otitis media demonstrate the similar effectiveness of cefixime 8 mg/kg daily (in 2 divided doses, or as a single daily dose), cefaclor 20 to 40 mg/kg daily and amoxycillin 40 mg/kg daily in 3 divided doses. The most frequently reported adverse effects, diarrhoea and stool changes, are usually mild to moderate in severity, transient, and mostly occur in the first few days of treatment with cefixime. Thus, cefixime is an effective orally active cephalosporin with a relatively long elimination half-life permitting a simplified treatment regimen. It is a suitable alternative to cefaclor or amoxycillin in acute otitis media and acute upper and lower respiratory tract infections, and to amoxycillin or co-trimoxazole in acute uncomplicated urinary tract infections.

beta-Lactamase stability and in vitro activity of oral cephalosporins against strains possessing well-characterized mechanisms of resistance

The in vitro activity of four oral cephalosporins was assessed in dilution tests with 50 isolates of the family Enterobacteriaceae possessing well-characterized mechanisms of resistance to beta-lactam antibiotics. The interaction of the drugs with a broad array of beta-lactamases was also determined in spectrophotometric assays and tests for enzyme induction. Overall, the percentages of strains susceptible to each of the study drugs were 82% for cefixime, 62% for cefuroxime, 58% for cephalexin, and 44% for cefaclor. The poor activity of the older cephalosporins was due to a high degree of susceptibility to hydrolysis by both plasmid-mediated and chromosomally mediated beta-lactamases. For cefaclor, higher MICs were associated with higher levels of plasmid-mediated beta-lactamases in the strains. Resistance to cefuroxime was seen primarily among strains expressing high levels of class I or IV beta-lactamase. Resistance to cefixime was seen only among strains expressing high levels of class I enzymes. Neither cefixime nor cefuroxime was a strong inducer of class I beta-lactamases, although enzyme induction did appear to play a role in cefuroxime resistance in a strain of Serratia marcescens. The consistently greater activity of cefixime over cefuroxime was found not to be due to greater drug permeation into the cell. Rather, it appeared to result from the high affinity of the drug for target enzymes.

In vitro antibacterial properties of cefetamet and in vivo activity of its orally absorbable ester derivative, cefetamet pivoxil

The in vitro activity of cefetamet, the microbiologically active metabolite of the orally administered prodrug cefetamet pivoxil, was compared with that of cephalexin, cefaclor, cefuroxime and amoxicillin. Cefetamet was highly active against Enterobacteriaceae, Neisseria spp., Vibrio spp., Haemophilus influenzae and streptococci other than enterococci. Cefetamet inhibited cefaclor-resistant species such as Proteus vulgaris, Providencia stuartii, Providencia rettgeri and Serratia marcescens. Staphylococci, Pseudomonas aeruginosa and cephalosporinase-overproducing strains of Enterobacter cloacae were resistant to cefetamet. The superior activity of cefetamet compared with older oral beta-lactam antibiotics against a large number of gram-negative pathogens correlated with enhanced stability towards beta-lactamases. In accordance with the in vitro findings, cefetamet pivoxil showed good activity in experimental infections in the mouse and rat, suggesting satisfactory bioavailability in these animals after oral administration.

In vitro and in vivo evaluations of a new broad-spectrum oral cephalosporin, BMY-28232, and its prodrug esters

The in vitro activity of a new cephalosporin, BMY-28232 (7-[(Z)-2-(2-aminothiazol-4-yl)-2-hydroxyiminoacetamido]-3-[ (Z)-1- propenyl]-3-cephem-4-carboxylic acid), was compared with those of cefuroxime and BMY-28488, the 3-vinyl congener of BMY-28232, against 899 bacteria including strains resistant to newer cephalosporins. BMY-28232 displayed potent, broad-spectrum antibacterial activity with high stability to various types of beta-lactamase. Its acetoxyethyl ester (BMY-28271) and pivaloyloxymethyl ester (BMY-28257) were well absorbed after oral administration to mice and rats. Both esters were metabolized to BMY-28232 and mainly excreted in urine. Oral bioavailability of both prodrug esters (60 to 70%) was better than that of cefuroxime axetil (46%) and gave excellent therapeutic efficacy against gram-positive- and gram-negative-bacterial infections in mice. Oral 50% protective doses (in milligrams per kilogram of body weight) of 0.65 and 0.72 for Staphylococcus aureus Smith, 0.9 and 1.2 for Escherichia coli Juhl, 1.6 and 1.6 for Proteus vulgaris, and 18.9 and 14.3 for Enterobacter cloacae were obtained for BMY-28271 and BMY-28257, respectively.

Bioequivalency of oral suspension formulations of cefixime

A study was performed in 24 healthy male subjects to establish that two suspension formulations of cefixime were bioequivalent to each other and to a reference oral solution. A single 400 mg oral dose of the drug was given in a randomized three-way crossover design as two suspensions (a research suspension (RS) used during clinical trials and a suspension intended for marketing (MS] and a reference oral solution (SOL). Each dose was separated from the other by a 3-day washout period. Mean peak serum concentrations (Cmax) were 4.67, 4.10, and 4.27 micrograms ml-1 after the MS, RS, and SOL, respectively. Although comparison (ANOVA) of the mean pharmacokinetic parameters for cefixime found significant differences (p less than 0.05) in Cmax, the time to Cmax, and area under the serum concentration time curve (AUC 0----infinity) values among the three formulations, the mean differences were less than 20 per cent. No significant differences (p greater than 0.05) were found in either the elimination half-life or renal clearance of unchanged drug. Overall, with a 98 per cent power to detect a 20 per cent difference in AUC0----infinity or urinary recovery values between the formulations tested, the results show that the MS was bioequivalent to the RS and that both suspensions were bioequivalent to the SOL.

Antimicrobial activity, spectrum, and recommendations for disk diffusion susceptibility testing of ceftibuten (7432-S; SCH 39720), a new orally administered cephalosporin

The antimicrobial activity and spectrum of ceftibuten (7432-S; SCH 39720) was determined on a wide variety of bacterial species selected for resistance to oral and parenteral beta-lactam antimicrobial agents. Ceftibuten was found to be the most active beta-lactam tested against members of the family Enterobacteriaceae, inhibiting 81.6% of strains at less than or equal to 8.0 micrograms/ml compared with 75.0 and 54.8% of strains inhibited by cefixime and cefuroxime, respectively. All strains of Haemophilus influenzae (MIC for 90% of strains [MIC90], less than or equal to 0.06 microgram/ml), Branhamella catarrhalis (MIC90, 3.0 micrograms/ml), and pathogenic Neisseria spp. (MIC90, less than or equal to 0.06 and 0.019 microgram/ml) were susceptible to ceftibuten. Beta-hemolytic Streptococcus spp. (serogroups A, B, C, and G) were also inhibited by ceftibuten, but penicillin-resistant pneumococci were generally resistant to cefixime and ceftibuten. The activity and spectrum of ceftibuten seem most applicable to infections of the respiratory and urinary tract plus those infections caused by pathogenic Neisseria spp. Ceftibuten disks (30 micrograms) were evaluated and found to have an acceptable correlation (r = 0.88) with ceftibuten MICs. Preliminary zone size interpretive criteria for MIC breakpoints of less than or equal to 4.0 and less than or equal to 8.0 micrograms/ml were calculated.

In vitro and in vivo antibacterial activities of ME1207, a new oral cephalosporin

ME1207 (pivaloyloxymethyl ester of ME1206) is a new oral cephalosporin. ME1206 is (6R,7R)-7-[(Z)-2-(2-aminothiazol-4-yl)-2-(methoxyimino)- acetamido]-3-[(Z)-2-(4-methylthiazol-5-yl)-ethyl]-cephem-4-carboxy lic acid. The susceptibilities of about 1,600 clinical isolates to ME1206 were determined by the agar dilution method. ME1206 showed a broad spectrum of activity against gram-positive and gram-negative bacteria. ME1206 was more active than cefaclor, T-2525, and cefixime against Staphylococcus aureus and Staphylococcus epidermidis. Against gram-negative bacteria, the activity of ME1206 was comparable with that of T-2525, but ME1206 was less active than cefixime. Against Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria gonorrhoeae, ME1206 had high activity (MIC, less than or equal to 0.05 microgram/ml). ME1206 was stable against various beta-lactamases, except beta-lactamases from Providencia rettgeri, Pseudomonas cepacia, and Escherichia coli W3630 (Rms213). The 50% effective doses of ME1207 after oral administration against systemic infections in mice were comparable with those of T-2588 against gram-negative bacteria and about one-fourth that of T-2588 against Staphylococcus aureus Smith.

Absolute bioavailability of cefixime in man

In a four-way cross-over study, the absolute bioavailability of cefixime was determined in 16 healthy volunteers. Each subject received a single 200-mg dose as an intravenous (IV) and oral solution, and 200-mg and 400-mg capsule doses of the drug. Blood and urine samples were collected for 24 hours after each dose. Cefixime was well tolerated after IV and oral doses of the drug and no serious drug-related adverse effects were observed. The maximal serum concentration (Cmax) of cefixime following the 200-mg oral solution and 200-mg and 400-mg capsule doses were 3.22, 2.92, and 4.84 micrograms/mL, respectively. Mean area under the serum concentration time curves (AUC) following the IV, 200-mg oral solution, and 200-mg and 400-mg capsule doses were 47.0, 26.0, 23.6, and 39.4 micrograms.hr/mL, respectively. Mean elimination half-life values of the drug were comparable after oral and IV doses, ranging from 3.2 to 3.5 hours. Based on serum AUC values, the absolute bioavailability of cefixime was 52.3%, 47.9%, and 40.2% after the 200-mg oral solution, 200-mg capsule and 400-mg capsule doses, respectively. Respective ratios based on 24-hour urinary recovery data were 44.7%, 41.7%, and 40.5%. Therefore, the results show that the percent of cefixime adsorbed after 200-mg and 400-mg oral doses was similar.

In vitro protein binding interaction studies involving cefixime

Cefixime is a new oral cephalosporin currently undergoing clinical trials. Selected agents with the likelihood for coadministration with cefixime in man were examined for their influence on the in vitro binding of cefixime in pooled serum from dog, monkey, and man. Results from these experiments showed no significant change in cerfixime binding in any animal species studied or in man by acetaminophen, heparin, phenytoin, diazepam, ibuprofen or furosemide at their maximum reported therapeutic concentrations. In contrast, both salicylic acid and probenecid resulted in concentration-dependent increases in the free fraction of cefixime (up to 2.5-fold). These findings demonstrate the usefulness of in vitro protein binding screening procedures for studying potential drug interactions that are mediated, at least in part, by changes in the protein binding of a drug.

In vitro activity of an oral iminomethoxy aminothiazolyl cephalosporin, R-3746

The in vitro activity of R-3746, an iminomethoxy aminothiazolyl cephalosporin with a CH2OCH3 moiety at position 3, was compared with those of other antibiotics. R-3746 inhibited the majority of hemolytic streptococci (groups A, B, C, F, and G) and Streptococcus pneumoniae at less than 0.06 micrograms/ml, which was comparable to the activity of amoxicillin, 2- to 8-fold more active than cefixime, and 16- to 64-fold more active than cefaclor and cephalexin. Ninety percent of beta-lactamase-producing Haemophilus influenzae and Neisseria gonorrhoeae were inhibited at a concentration 0.25 micrograms/ml, but it was less active against Branhamella spp. It did not inhibit (MIC, greater than 16 micrograms/ml) enterococci, viridans group streptococci, or methicillin-resistant staphylococci. The MICs of R-3746 for 90% of strains tested for Escherichia coli; Klebsiella pneumoniae; Citrobacter diversus; Proteus mirabilis; and Salmonella, Shigella, and Yersinia spp. were less than or equal to 1 micrograms/ml. It was two- to eightfold less active than cefixime but was markedly superior to cefaclor, cephalexin, amoxicillin-clavulanate, and trimethoprimsulfamethoxazole. R-3746 inhibited 50% of Enterobacter cloacae, Enterobacter aerogenes, Citrobacter freundii, Morganella spp., Providencia spp., Proteus vulgaris, and Serratia marcescens at less than or equal to 8 micrograms/ml. Pseudomonas spp. were resistant. Fifty percent of Clostridium spp. were inhibited by 0.5 micrograms/ml, but MICs for Bacteroides spp. were greater than 128 micrograms/ml. R-3746 was not appreciably hydrolyzed by most chromosomal and plasmid-mediated beta-lactamases.

Antimicrobial activity and disk diffusion susceptibility testing of U-76,253A (R-3746), the active metabolite of the new cephalosporin ester, U-76,252 (CS-807)

Compound U-76,253A (R-3746), the active metabolite sodium salt of the prodrug ester U-76,252 (CS-807), was demonstrated to be active against members of the family Enterobacteriaceae with 82 and 85% of strains inhibited by less than or equal to 2.0 and less than or equal to 4.0 micrograms/ml, respectively. In addition, U-76,253A inhibited all strains of Branhamella catarrhalis, Haemophilus influenzae, pathogenic Neisseria spp., oxacillin-susceptible Staphylococcus aureus, beta-hemolytic streptococci, and pneumococci at less than or equal to 4.0 micrograms/ml. Pseudomonas spp., Acinetobacter spp., enterococci, and oxacillin-resistant staphylococci were resistant to U-76,253A. This U-76,253A antimicrobial activity and spectrum was generally superior to that of comparison orally administered cephems (cefaclor, cefuroxime, and cefixime) and the amoxicillin-clavulanic acid combination. Tests with beta-lactamase-producing isolates indicated that U-76,253A was bactericidal and that its MICs were only influenced by high inoculum concentrations (10(7) CFU/ml) against type Ia and IVc enzyme-producing strains. Preliminary disk diffusion interpretive zone criteria were calculated for 10- and 30-micrograms U-76,253A disks and several possible susceptible MIC breakpoints. The absolute interpretive agreement between MICs and zone diameters ranged from 87.8 to 95.6%. Final selection of interpretive criteria awaits further U-76,252 pharmacokinetic information.

Impact of cefixime on the normal intestinal microflora

The ecological effects on the normal intestinal microflora after cefixime tablets in doses of 200 mg twice daily for 7 days were studied in 10 healthy volunteers. Stool specimens were collected before and 2, 4, 7, 14 and 21 days after start of treatment. Plasma samples were collected during 12 h after the first dose on day 1 and 1 sample was taken on day 7 for bioassay of cefixime concentration. Peak plasma concentration of cefixime occurred after about 4 h with a mean of 3.0 mg/l. The mean AUC0----oc after a single dose was estimated at 21.9 mg x h/l and the mean elimination half-life was 3.9 h. The mean plasma concentration of cefixime 3 h after the morning dose on day 7 was 2.0 mg/l. The concentrations of cefixime in faeces increased during treatment. One subject had detectable concentrations in faeces on day 2, three subjects on day 4 and 8 subjects on day 7 in the order of 237-912 mg/kg faeces. There was a marked decrease in the numbers of streptococci and Escherichia coli and an increase in the numbers of enterococci during the administration of cefixime. In the anaerobic microflora, the numbers of cocci, clostridia and bacteroides were suppressed while there were minor changes in the numbers of bifidobacteria. Clostridium difficile was isolated in 5 subjects on day 7 but cytotoxin was only detected in one subject. The intestinal microflora was normalized within 2 weeks after treatment had stopped. Slightly soft stools were reported by 7 subjects. One subject had abdominal pain and diarrhoea 1 week after treatment followed by anal irritation and itching.(ABSTRACT TRUNCATED AT 250 WORDS)

Antimicrobial activity of U-76,252 (CS-807), a new orally administered cephalosporin ester, including recommendations for MIC quality control

U-76,253A (R-3746), the active metabolite of the new cephalosporin ester, U-76,252 (CS-807), was tested against 4,742 fresh clinical isolates from four large medical centers. U-76,253A was very active against nearly all species of Enterobacteriaceae (87.7% inhibited at less than or equal to 4.0 micrograms/ml). Staphylococcus spp., and the streptococci. The U-76,253A spectrum was superior to the comparison orally administered cephalosporins (cephalexin, cephradine, cefaclor). Pseudomonas spp., Acinetobacter spp., and the enterococci were resistant to U-76,253A and the other tested drugs. Broth microdilution MIC quality control (QC) limits were established for U-76,253A in a multilaboratory investigation using a minimum of 125 MIC determinations per organism. The following MIC QC ranges were recommended; Escherichia coli (ATCC 25922) = 0.25-1.0 micrograms/ml, Staphylococcus aureus (ATCC 29213) = 2.0-4.0 micrograms/ml and Pseudomonas aeruginosa (ATCC 27853) = greater than 32 micrograms/ml.

In vitro evaluations of U-76,252 (CS-807): antimicrobial spectrum, beta-lactamase stability, and enzyme inhibition

Compound U-76,252 (Upjohn) is a cephalosporin ester that enhances oral absorption of the active free acid cephem, U-76,253. The active form structurally resembles parenteral aminothiazolyl-methoxyimino cephalosporins such as cefotaxime and its desacetyl metabolite. The g-negative antimicrobial activity of U-76,253 A (sodium salt of U-76,253) was most similar to that of cefixime and more potent than that of cefaclor or cefuroxime among the orally administered cephalosporins. Against g-positive bacteria, U-76,253 A was more active than cefixime. U-76,253 A was relatively stable to hydrolysis by five beta-lactamases (Type Ia, TEM-1, K1, CARB-2, and OXA-1), a stability most similar to cefotaxime and superior to that of cefaclor. Only the Type Ia (P99) enzyme was significantly inhibited by U-76,253 (IC 50 = 2.0 microM).

Determination of cefixime in biological samples by reversed-phase high-performance liquid chromatography

A simple, accurate and precise isocratic reversed-phase high-performance liquid chromatographic method has been developed and validated for the determination of a new cephalosporin in human serum and urine. Human serum samples, calibration standards and quality control samples (250 microliter) were combined with an equal volume of 6% trichloroacetic acid (TCA). Human urine (0.1 ml) was combined with 6% TCA solution containing the internal standard. The compounds were detected by ultraviolet absorbance set to 280 nm for the serum assay and 313 nm for the urine assay. The method for the determination of cefixime in serum was linear from 100 ng/ml to 30.0 micrograms/ml (r = 0.999), and for the urine assay from 5 micrograms/ml to 100 micrograms/ml (r = 0.999). The minimum reportable quantity for the serum assay was 0.05 microgram/ml. The within- and between-day assay variation for both assays were found to be less than 10% in an extensive assay validation scheme. Results of a storage stability study indicated that human serum and urine samples could be safely stored for up to six months at -18 degrees C and three months at -10 degrees C, respectively.

In vitro susceptibility of Haemophilus influenzae to cefixime

The in vitro activity of cefixime against 2,458 clinical isolates of Haemophilus influenzae was determined. All the strains were inhibited by less than or equal to 2 micrograms of cefixime per ml, and the modal MIC was 0.03 micrograms/ml. Activity was unaffected by the presence of beta-lactamase produced by 157 isolates. Nineteen of the twenty-four isolates for which cefixime MICs were greater than or equal to 0.5 micrograms/ml were beta-lactamase negative but showed reduced susceptibility to ampicillin.

Pharmacokinetics of cefixime after once-a-day and twice-a-day dosing to steady state

The pharmacokinetics of cefixime (CL 284,635; FK027), a new orally active broad-spectrum cephalosporin, were determined in 26 healthy volunteers, after multiple 200-mg twice-a-day (group 1; N = 13) or 400-mg once-a-day (group 2; N = 13) dosing for 15 days. On study days 1, 8, and 15, mean peak serum concentrations (Cmax) were 1.67, 1.75, and 1.87 micrograms/mL, respectively, for group 1 and 2.76, 3.04, and 2.67, respectively, for group 2. Over the 15-day period, mean trough serum concentrations were, on average, 0.40 and 0.08 microgram/mL for groups 1 and 2, respectively. Comparison (ANOVA) of serum and urinary excretion pharmacokinetic parameters for cefixime on days 1, 8, and 15 found no significant (P greater than .05) differences for either group except for a small but significantly (P less than .05) earlier time to reach Cmax and higher renal clearance on days 8 and 15 in group 1. These differences, however, are not clinically significant. On study days 1, 8, and 15, mean Cmax and AUC0-tau values for Group 2 were about 1.5 to 2.2 time those for Group 1. Urinary excretion of cefixime accounted for 11.9 to 14.5% and 9.9 to 12.4% of the dose in groups 1 and 2, respectively, over the 15-day study. Overall, there was no accumulation of cefixime in serum or urine nor was there a reduction in serum concentrations of urinary amounts over the 15-day dosing period when the drug was given either as a 200-mg twice-a-day or 400-mg once-a-day dosing regimen.

Preliminary antimicrobial susceptibility interpretive criteria for cefetamet (Ro 15-8074) and cefteram (Ro 19-5247) disk tests

Preliminary interpretive zone criteria were calculated for cefetamet (Ro 15-8074) and cefteram (Ro 19-5247) by using 10- and 30-micrograms disks and three possible MIC susceptibility breakpoints. Absolute interpretive agreement between MICs and zone size criteria ranged from 91.8 to 97.2%. Very major errors (false susceptibility) were less than or equal to 1.2% for both cephalosporin disk tests. Morganella morganii strains appeared to produce the highest rates of very major interpretive errors with cefetamet disks.

World-wide development of antibiotic resistance in pneumococci

Antibiotic-resistant pneumococci, especially penicillin-resistant strains, are being increasingly isolated. Pneumococci with intermediate penicillin-resistance (MIC 0.1-1.0 micrograms/ml) have been reported from many parts of the world over the past two decades, and highly resistant strains (penicillin MICs greater than or equal to 2 micrograms/ml) have also appeared. Infection may be acquired in the hospital or community, and nosocomial outbreaks may occur which require control measures to limit organism spread. Most infections occur in children with diminished host responses. Disease caused by pneumococci with intermediate penicillin-resistance may be treated with high doses of penicillin, but disease caused by highly resistant strains, especially meningitis, may require alternative therapy. Pneumococci resistant to sulfonamides, tetracyclines, erythromycin, lincomycin, clindamycin, chloramphenicol, aminoglycosides and rifampin have also appeared. Strains resistant to all the above-mentioned agents, including all beta-lactam antibiotics tested, have been reported from South Africa and Spain. Alternative therapy for resistant strains may include vancomycin, cefotaxime, cefoperazone, ceftriaxone and imipenem. Pneumococci isolated from sites suggestive of infection, especially blood and cerebrospinal fluid, should be routinely tested for penicillin-susceptibility.