In vitro activities of 15 oral beta-lactams against Klebsiella pneumoniae harboring new extended-spectrum beta-lactamases

In VitroSelection and Characterization of Mutants in TEM-1-ProducingEscherichia coliby Ceftazidime and Ceftibuten

The present work was undertaken to study the ability of ceftazidime and ceftibuten to selectin vitro Escherichia coli HB101 harboring bla(TEM-1) beta-lactamase gene. Minimum inhibitory concentrations (MICs) of ceftazidime and ceftibuten were increased by a factor of 32, overcoming in the case of ceftazidime the breakpoint for clinical resistance. Outer membrane protein analysis and PCR for bla(TEM )alleles revealed that ceftazidime and ceftibuten select for different resistance mechanisms. Ceftazidime created mutants that encode an extended-spectrum beta-lactamase (TEM-12) and exhibit decreased expression of OmpF. Ceftibuten was unable to select for extended-spectrum beta-lactamase expressing mutants but reduced the expression of two porins, OmpC and OmpF. The stability of ceftibuten to hydrolysis and the difference in the structure of these beta-lactam antibiotics could be responsible for the selection of different mechanisms of resistance.

Imipenem and meropenem: Comparison of in vitro activity, pharmacokinetics, clinical trials and adverse effects

OBJECTIVE

To compare and contrast imipenem and meropenem in terms of in vitro activity, pharmacokinetics, clinical efficacy and adverse effects.

DATA SELECTION

MEDLINE search from 1975 to 1997 and follow-up of references.

DATA EXTRACTION

Clinical trials comparing imipenem with meropenem, or either imipenem or meropenem with standard therapy in the treatment of serious infections were selected.

DATA SYNTHESIS

Imipenem, the first carbapenem, was first marketed in 1987; meropenem was introduced to the market in 1996. In general, imipenem is more active against Gram-positive cocci while meropenem is more active against Gram-negative bacilli. The agents display similar pharmacokinetics. Clinical studies in patients with serious infections (intra-abdominal infection, respiratory infection, septicemia, febrile neutropenia) report similar bacteriological and clinical cure rates with imipenem and meropenem. Meropenem is approved for the treatment of bacterial meningitis, whereas imipenem is not. Adverse effects are similar.

CONCLUSIONS

Current literature supports the use of imipenem at a dose of 500 mg every 6 h and meropenem at 1 g every 8 h for the treatment of severe infections. For the treatment of serious infections, imipenem (500 mg every 6 h or 2 g/day [$98/day]) is more economical than meropenem (1 g every 8 h or 3 g/day [$142/day]) based on acquisition cost.

ARI 1: beta-lactamase-mediated imipenem resistance in Acinetobacter baumannii

A strain of Acinetobacter baumannii 6B92 isolated from the blood culture of a patient at the Edinburgh Royal Infirmary i 1985 was found to be resistant to imipenem, all classes of cephalosporins and penicillins. Extraction of the soluble proteins of the cell and isoelectric focusing revealed the presence of two beta-lactamases: a chromosomal cephalosporinase of high pI (> pI 9.0) and a novel beta-lactomase of pI 6.65 named ARI 1 (Acinetobacter resistant to imipenem). Despite the fact that original clinical isolate could be 'cured' of its resistance to imipenem and penicillins by growing in the presence of ethidium bromide with the concurrent loss of the ARI 1 enzymes, no resistance plasmid was visualised or transferred. The ARI 1 beta-lactamase hydrolysed penicillin, ampicillin and cephaloridine slowly during enzyme assay but inactivation of imipenem could only be demonstrated by microbiological means. The molecular size of the ARI 1 enzyme was 23 kDa and it was not inhibited by EDTA, p-CMB, or clavulanate.

The Bla2 beta-lactamase from the live-vaccine strain of Francisella tularensis encodes a functional protein that is only active against penicillin-class beta-lactam antibiotics

Francisella tularensis ssp. tularensis is a category A select agent and the causal organism for the zoonotic disease tularemia. The vast majority of F. tularensis isolates are beta-lactamase-positive. beta-lactamase production is widely believed to be responsible for the inefficacy of beta-lactams in the treatment of tularemia. In this study, we report the cloning and characterization of the two chromosomally encoded F. tularensis ssp. holarctica live-vaccine strain (LVS) beta-lactamases. The two LVS beta-lactamases were homologous to F. tularensis Schu S4 open reading frames FTT0681c and FTT0611c and have been named bla1 (LVS) and bla2 (LVS), respectively. Recombinant expression in Escherichia coli suggested that bla1 (LVS) did not encode a functional beta-lactamase, whereas bla2 (LVS) encoded a functional beta-lactamase that hydrolyzed penicillins but was inactive against third-generation cephalosporins, including cefprozil. As both LVS and Schu S4 were susceptible to cefprozil, we developed three new shuttle vectors based on selection for the production of the Bla(shv-2) extended-spectrum beta-lactamase with cefprozil. The resulting shuttle vectors were suitable for recombinant gene expression and complementation studies in LVS and Schu S4.

Bactericidal activity of oral β-lactam antibiotics in plasma and urine versus isogenic Escherichia coli strains producing broad- and extended-spectrum β-lactamases

Bacteria harbouring extended-spectrum beta-lactamases (ESBLs), derived by mutation from TEM-1, TEM-2 or SHV-1 beta-lactamases, have been described world-wide. The in vitro activities of these enzymes against beta-lactam antibiotics, including oral cephalosporins, are well recognised. The aim of this investigation was to assess the bactericidal activity of oral beta-lactam antibiotics available in Croatia (amoxicillin/clavulanate, cephalexin, cefuroxime, cefadroxil and ceftibuten), in biological fluids against isogenic Escherichia coli strains producing broad-spectrum (TEM-1, TEM-2 and SHV-1) and extended-spectrum beta-lactamases (SHV-2, SHV-3, SHV-4, SHV-5, SHV-12). Bactericidal activity of oral beta-lactams in plasma and urine was tested in time-kill experiments and by determining bactericidal titres at different time intervals post-dose. The killing rate of antibiotics in urine was slower than in plasma, but faster than in Mueller-Hinton broth. High bactericidal titres in urine were only maintained throughout the whole dosing interval by ceftibuten against strains producing broad-, SHV-2 and SHV-3 beta-lactamases. The older generation cephalosporins can be considered for the therapy of urinary tract infections caused by E. coli harbouring TEM-1, TEM-2 and SHV-1 beta-lactamases but a shorter dosing interval is needed. Ceftibuten can be recommended with caution in ESBL producing E. coli except those producing SHV-4, SHV-5 and SHV-12 that confer resistance to it. If these enzymes are produced, fluoroquinolones or carbapenems could be considered.

Ceftibuten stability to active-site serine and metallo-beta-lactamases

Ceftibuten is an oral third-generation cephalosporin active against a wide range of bacteria and shows an improved stability to hydrolysis by several beta-lactamases because of the carboxyethilidine moiety at position 7 of the ss-acyl side chain. The kinetic interactions between ceftibuten and active-site serine and metallo-ss-lactamases were investigated. The activity of several TEM-derived extended spectrum beta-lactamases (ESbetaLs) against ceftibuten, cefotaxime and ceftazidime was compared using K(m), K(cat) and K(cat)/K(m). Ceftibuten behaved as a poor substrate for class A and B beta-lactamases compared with cefotaxime. The chromosomal class C beta-lactamase from Enterobacter cloacae 908R gave a high K(cat) value (21 s(-1)), whereas there was poor activity with enzymes from Acinetobacter baumannii and Morganella morganii and ceftibuten. Ceftibuten resists hydrolysis in the presence of typical respiratory or urogenital-tract pathogens producing beta-lactamases.

Ceftibuten: a new expanded-spectrum oral cephalosporin

OBJECTIVE

To review the antimicrobial activity, pharmacokinetics, clinical efficacy, and tolerability of ceftibuten, a new expanded-spectrum oral cephalosporin.

DATA SOURCES

Literature was identified by a MEDLINE search (January 1983-June 1996) of the medical literature, review of English-language literature and bibliographies of these articles, and data on file.

STUDY SELECTION

Clinical efficacy data were selected from all published and unpublished trials and abstracts that mentioned ceftibuten. Additional information concerning in vitro susceptibility, safety, chemistry, and pharmacokinetic profile of ceftibuten also was reviewed.

DATA SYNTHESIS

Ceftibuten, an oral expanded-spectrum cephalosporin, has a broad spectrum of activity against many gram-negative and selected gram-positive organisms, including Streptococcus pneumoniae, Streptococcus pyogenes, Moraxella catarrhalis, and Haemophilus influenzae. Ceftibuten is stable to hydrolysis by many common beta-lactamases. Ceftibuten is rapidly and almost completely absorbed from the gastrointestinal tract and is primarily eliminated renally as unchanged drug. The elimination half-life of ceftibuten is slightly longer than 2 hours. Efficacy has been demonstrated in a number of clinical trials in adults and children with upper and lower respiratory tract infections (e.g., acute otitis media, pharyngitis, sinusitis, bronchitis) and urinary tract infections. The adverse effect profile is equal to that of comparator agents.

CONCLUSIONS

Ceftibuten is an alternative to other antimicrobial agents with convenient once-daily dosing in the treatment of upper and lower respiratory tract infections. Similar to other oral expanded-spectrum cephalosporins, ceftibuten has antimicrobial activity against common pathogens of the respiratory tract and is stable in the presence of many beta-lactamases. The clinical choice of an oral expanded-spectrum cephalosporin will be based on patient acceptance, frequency of administration, and cost.

A review of the in vitro activity of meropenem and comparative antimicrobial agents tested against 30,254 aerobic and anaerobic pathogens isolated world wide

The in vitro activity of meropenem (formerly SM-7738), a new carbapenem, was compared with that of imipenem and five other broad-spectrum antimicrobials (ceftazidime, cefotaxime, piperacillin, piperacillin/tazobactam, and ciprofloxacin) against 30,254 clinically significant pathogens isolated in nine countries worldwide. Overall, the carbapenems, meropenem and imipenem, were the most active drugs. Meropenem was four- to 64-fold more active than imipenem against Gram-negative bacteria, including the Enterobacteriaceae, Pseudomonas aeruginosa, Burkholderia cepacia, Haemophilus influenzae, and Neisseria meningitidis. Meropenem was also quite active against ceftazidime-resistant strains of Enterobacteriaceae, inhibiting 87.5 to 100% at < or = 4 micrograms/ml. In contrast, imipenem was four- to eight-fold more active than meropenem against Gram-positive species, including methicillin-susceptible strains of Staphylococcus aureus and Staphylococcus epidermidis, Streptococcus pneumoniae, and Enterococcus faecalis. Among the anaerobes, strains resistant to meropenem or imipenem were encountered very rarely. These extensive data provide additional in vitro support for the clinical use of meropenem as a broad spectrum antimicrobial agent active against key pathogenic species of bacteria.

A national collaborative study of the in vitro activity of oral cephalosporins and loracarbef (LY 163892). Australian Group for the Study of Antimicrobial Resistance (AGAR)

A national collaborative study involving the laboratories of 17 Australian hospitals examined the in vitro activity of loracarbef, cefaclor, cephalexin, amoxycillin and amoxycillin/clavulanate against 2661 recently isolated common bacterial pathogens. Loracarbef was the most active agent against Escherichia coli (MIC90 = 1 mg/l) and had activity comparable to other agents against Klebsiella pneumoniae and Proteus mirabilis. Like the oral cephalosporins, it had no activity against species of Enterobacter and Serratia. beta-lactamase-producing Staphylococcus aureus and Haemophilus influenzae were moderately sensitive to loracarbef (MIC90 = 8 mg/l for both species). Streptococcus pneumoniae was moderately sensitive to loracarbef (MIC90 = 2 mg/l) but strains which were insensitive to penicillin were often highly resistant.

Activities of oral antibiotics on Providencia strains isolated from institutionalized elderly patients with urinary tract infections

More than 250 Providencia strains isolated from the urine of institutionalized elderly patients were tested against cefaclor, cefuroxime, cefetamet, cefpodoxime, ciprofloxacin, and amoxicillin-clavulanic acid. Our results confirm the strong activities of expanded-spectrum oral cephalosporins against Providencia isolates, f1p4ell as the marked differences in susceptibilities among accurately identified Providencia species.

Meropenem. A review of its antibacterial activity, pharmacokinetic properties and clinical efficacy

The parenteral carbapenem meropenem is relatively stable to inactivation by human renal dehydropeptidase (DHP-1) and does not require concomitant administration of a DHP-1 inhibitor such as cilastatin. It has a broad spectrum of antibacterial activity in vitro, the majority of Gram-negative, Gram-positive and anaerobic pathogens being highly susceptible to the drug. Meropenem has shown clinical and bacteriological efficacy in the treatment of a wide range of serious infections in adults and children which is at least comparable with that of currently available treatment options. Its clinical and bacteriological efficacy is similar to that of imipenem/cilastatin, clindamycin plus tobramycin and cefotaxime plus metronidazole in the treatment of intraabdominal infections; cefotaxime or ceftriaxone in the treatment of meningitis; imipenem/cilastatin, and ceftazidime with or without an aminoglycoside, in lower respiratory tract infections; and imipenem/cilastatin or ceftazidime in the treatment of urinary tract infections. Satisfactory clinical and bacteriological response rates have also been achieved in patients with skin and skin structure infections, obstetric and gynaecological infections or septicaemia, and in immunocompromised patients with febrile episodes. Preliminary findings also indicate efficacy in the treatment of respiratory tract infections in patients with cystic fibrosis. The tolerability profile of meropenem is generally similar to that of comparator agents, although it is associated with a lower incidence of adverse gastrointestinal effects (nausea and vomiting) than imipenem/cilastatin. Importantly, the incidence of seizures in patients with meningitis is not increased following administration of meropenem. Thus, meropenem is an effective broad spectrum antibacterial drug for the treatment of a wide range of infections including polymicrobial infections in both adults and children, with comparable efficacy to imipenem/cilastatin and various other treatment regimens. Meropenem is likely to be of greatest value as empiric monotherapy in the treatment of serious infections for those caused by multiply-resistant pathogens. Further clinical experience is necessary, however, to ultimately define its place in therapy.

Transferable resistance to cefotaxime in nosocomial Klebsiella pneumoniae and Escherichia coli strains due to their production of extended-spectrum beta-lactamase in Slovakia

Transferable resistance to cefotaxime was demonstrated in 21 nosocomial strains of Klebsiella pneumoniae and Escherichia coli subsequently isolated from patients in two large University clinics. Using the double-disk diffusion test, we could detect, in each such strain, as well as in E. coli 3110 K-12 transconjugants after the transfer, the production of an Extended Spectrum Beta-Lactamase (ESBL). Ceftibuten was demonstrated to be effective against the majority of strains studied.

Comparative microbiological activity and pharmacokinetics of cefprozil

In vitro studies on the activity of cefprozil have been conducted in Europe and North America. Against gram-negative bacilli, cefprozil and cefaclor are at least two to four times more active than cephalexin. Cefixime is more active against these organisms. Against gram-positive cocci, cefprozil is at least two to four times more active than cefaclor and cephalexin; cefixime has limited gram-positive activity, and is particularly inactive against staphylococci (MIC90 32 mg/l). Cefprozil is highly active against Streptococcus pneumoniae (unlike cefixime). Those strains of this genus that display intermediate resistance to pneumococci are more susceptible to cefprozil than cefaclor. Neisseria species and Moraxella catarrhalis are susceptible to cefprozil (MIC90 0.06 and 1 mg/l). beta-lactamase-producing strains of Haemophilus influenzae appear to be susceptible to cefprozil, as the reported MIC90 is 2-4 mg/l. Enterococci, Pseudomonas aeruginosa, and those strains of the Enterobacteriaceae that commonly possess a chromosomal cephalosporinase (e.g., Providencia, Morganella and Enterobacter) are generally considered to be resistant to cefprozil as well as to other oral cephalosporins. Cefprozil appears to display enhanced stability to the commonly encountered Tem-1 and SHV-1 plasmid-mediated beta-lactamases, as found in Haemophilus influenzae, Neisseria gonorrhoeae and the Enterobacteriaceae. Cefprozil is rapidly absorbed, reaching a maximum concentration 0.9 to 1.2 h post-dose. Following oral doses of 250 and 500 mg, the Cmax is 6.2 and 10.0 mg/l respectively. Serum half-lives are generally reported as between 1.2 and 1.4 h, and urine recovery is high, 57-70%.(ABSTRACT TRUNCATED AT 250 WORDS)

Ceftibuten. A review of its antibacterial activity, pharmacokinetic properties and clinical efficacy

Ceftibuten is an orally active third generation cephalosporin which has a broad spectrum of in vitro antibacterial activity, encompassing the majority of Gram-negative pathogens and streptococci, and which shows greater stability than several other cephalosporins against bacteria producing extended-spectrum beta-lactamases. In clinical studies, ceftibuten (generally 400 mg/day in adults or 9 mg/kg/day in children, administered once daily) was effective in the treatment of acute uncomplicated or complicated urinary tract infections, demonstrating an efficacy similar to that of cefaclor (1500 mg/day), and similar or superior to that of cotrimoxazole (trimethoprim/sulfamethoxazole; 8/40 mg/kg/day) in children. The majority of patients with acute or chronic lower respiratory tract infections responded to treatment with ceftibuten, and response rates were similar to those achieved with cefaclor (750 or 1500 mg/day). Ceftibuten 9 mg/kg/day was at least as effective as cefaclor and as effective as amoxicillin/clavulanic acid (both 40 mg/kg/day) in children with acute otitis media, and was superior to phenoxymethylpenicillin (penicillin V; 25 mg/kg/day) in children and adolescents with streptococcal pharyngitis or scarlet fever caused by Group A beta-haemolytic streptococci. Ceftibuten was well tolerated in most patients, with adverse events (mostly mild to moderate gastrointestinal disturbances) generally occurring in 5 to 10% of patients. Thus, ceftibuten, with a once- or twice-daily oral dosage regimen, good tolerability profile and activity against a wide range of bacterial organisms, offers a promising alternative to other agents (including cefaclor, cotrimoxazole, amoxicillin/clavulanic acid, bacampicillin and phenoxymethylpenicillin) for the treatment of patients with urogenital and respiratory tract infections. Its place in therapy will be more clearly defined following further large comparative trials, in which it is likely to prove most useful in patients with infections caused by beta-lactamase-producing pathogens.

Ceftibuten pharmacokinetics and pharmacodynamics. Focus on paediatric use

Ceftibuten is an extended-spectrum, cephem antimicrobial agent formulated for oral administration. Ceftibuten is absorbed by carrier-mediated processes and passive diffusion. The absorption of ceftibuten is described adequately by a first-order process. Following oral administration, peak serum ceftibuten concentrations are reached within 2 to 3 hours. Although the absolute bioavailability of ceftibuten in humans is not known, its relative bioavailability indicates that there is relatively rapid and complete absorption of the drug. Administration of ceftibuten with food may decrease the rate of absorption and, in the case of high fat meals, may decrease the extent of absorption by approximately 20 to 30%. The results of limited studies indicate that the drug distributes well into various body tissues and fluids, with relatively high concentrations being achieved in organs that receive a significant portion of the cardiac output. In adults with normal renal function or chronic renal failure, the apparent volume of distribution (Vd/F) for ceftibuten ranges from 0.2 to 0.4 L/kg and the total plasma clearance (CL/F) ranges from approximately 61 to 75 ml/min (3.7 to 4.5 L/h). Studies of ceftibuten elimination in adults have demonstrated positive linear correlation between CL/F and creatinine clearance. Following administration of a single dose of ceftibuten, approximately 67 to 94% of the drug has been recovered in the urine unchanged. The elimination half-life (t1/2 beta) of ceftibuten in adults with normal renal function is approximately 2.5 hours. Significant accumulation of ceftibuten does not occur with repeated administration. Despite the fact that the mean time taken to achieve maximal serum concentration (tmax) [1.1 to 2 hours] and t1/2 beta (2.1 hours) following administration of a single dose of ceftibuten to infants and children were similar to values previously reported in adults, the Vd/F (0.42 L/kg) and CL/F (3.1 ml/h/kg) were considerably greater in children younger than 5 years. Additionally, the apparent nonrenal clearance of ceftibuten in paediatric patients (52% of CL/F) was greater than reported for adults (approximately 32% of CL/F) with normal renal function. Thus, developmental differences appear to affect the pharmacokinetic profile of ceftibuten. Ceftibuten has a wide spectrum of antimicrobial activity against both Gram-positive and Gram-negative pathogens, and is stable to hydrolysis by a large number of beta-lactamases. Notable exceptions with regard to the Gram-positive spectrum for ceftibuten include relative or documented resistance for most strains of Listeria, Staphylococcus aureus, S. epidermidis, penicillin-resistant strains of Streptococcus pneumonia and S. enterococcus.(ABSTRACT TRUNCATED AT 400 WORDS)

Stability in the presence of widespread beta-lactamases. A prerequisite for the antibacterial activity of beta-lactam drugs

Bacterial resistance to the beta-lactam drugs is extremely widespread, as a result of extensive drug use. Loss of susceptibility is primarily attributable to hydrolysis by inactivating enzymes, namely the beta-lactamases. While the number of characterised beta-lactamases may exceed 100, only a few are a problem in the treatment of community-acquired infections (TEM-1, TEM-2, SHV-1, BRO-1). Chromosomally mediated and extended-spectrum beta-lactamases are usually dominant in nosocomial pathogens where oral antibiotic therapy is seldom used. Therefore, the threat posed by beta-lactamases must be considered in general practice. Several effective strategies have been implemented in order to overcome beta-lactamase-mediated resistance, e.g. use of non-beta-lactam drugs or beta-lactamase inhibitors. Another option has been the development of new beta-lactam compounds that possess a high intrinsic stability against the hydrolytic action of common beta-lactamases. Among these compounds, the oral third generation cephalosporins represent an important breakthrough. Cefetamet pivoxil, a new oral third generation cephalosporin, is characterised by excellent antimicrobial potency against Enterobacteriaceae, and Moraxella (Branhamella) catarrhalis and Haemophilus influenzae, irrespective of their ability to produce beta-lactamases. The Gram-positive respiratory pathogens, Streptococcus pyogenes and penicillin-susceptible S. pneumoniae, are also satisfactorily covered. The activity of cefetamet has recently been corroborated in a survey conducted in Italy involving 4191 isolates. However, cefetamet shows no activity against enterococci, staphylococci, Listeria, alpha-streptococci, Pseudomonas, Acinetobacter and anaerobes. Given this antibacterial profile, cefetamet pivoxil may provide a useful alternative to other oral antibacterial agents in the empirical therapy of acute community-acquired respiratory and urinary tract infections. From the results of the Italian survey, cefetamet emerged as the only agent among those considered (which included cefuroxime, cefaclor, cefalexin, cefadroxil, ampicillin, amoxicillin/clavulanic acid, ampicillin/sulbactam, doxycycline, erythromycin and clindamycin) that might be selected as the drug of choice in the empirical therapy of outpatient infections.

Origin and impact of plasmid-mediated extended-spectrum beta-lactamases

Resistance to oxyimino cephalosporins was originally highlighted by the emergence of plasmid-encoded extended-spectrum beta-lactamases deriving by mutation from TEM-1, TEM-2 and SHV type enzymes (class A). The broader spectrum of resistance produced by these enzymes is related to more amino acid substitutions, but susceptibility to seven alpha-methoxyimino cephalosporins and carbapenems was preserved until recently. Clavulanate-sensitive extended-spectrum beta-lactamases are distributed worldwide, mainly among Klebsiella pneumoniae isolates. Novel clavulanate-sensitive extended-spectrum beta-lactamases deriving from other class A enzymes (e.g. MEN-1 from beta la OXY, OXA-11 in Pseudomonas aeruginosa from PSE-2) have been reported. Recently, clavulanate-resistant extended-spectrum beta-lactamases (class C) were encountered amongst single isolates, mostly Klebsiella pneumoniae. These cephalosporinases or cefamycinases (usually chromosomally mediated) have expanded the spectrum of plasmid-encoded resistance to include seven alpha-methoxyimino cephalosporins. Thus far, only two isolates (1 Pseudomonas aeruginosa, 1 Bacteroides fragilis), both recovered in Japan, with plasmid-mediated resistance to carbapenems have been found.

Cefetamet pivoxil clinical pharmacokinetics

Cefetamet pivoxil is an orally absorbed prodrug ester of the microbiologically active cephalosporin, cefetamet. The prodrug ester is completely hydrolysed to the active compound cefetamet on its first pass through the gut wall, the liver or both. Cefetamet is classified as a third generation cephalosporin with excellent activity against streptococci, Enterobacteriaceae, Neisseria and Haemophilus species. It has enhanced stability against beta-lactamases compared with penicillins and first and second generation cephalosporins. The antibacterial spectrum is comparable with that of cefotaxime except for its poor activity against staphylococci. Following a 20-minute zero-order intravenous infusion, cefetamet had a rapid distribution phase followed by a monoexponential decline. The average pharmacokinetic parameters from 152 healthy volunteers were: total body clearance 136 ml/min (8.16 L/h); renal clearance 119 ml/min (7.14 L/h); nonrenal clearance 17 ml/min (1.02 L/h); volume of distribution at steady-state 0.29 L/kg; terminal elimination half-life 2.2 hours; 88% of the dose recovered in the urine. Cefetamet is not extensively bound to plasma proteins. Consequently, these data indicate that cefetamet is predominantly eliminated unchanged by the kidney via glomerular filtration with possibly a minor component of tubular secretion. Cefetamet has a relatively small apparent volume of distribution consistent with that of other beta-lactam antibiotics. Results following ascending intravenous doses of cefetamet in healthy young male volunteers demonstrated that the pharmacokinetics of intravenous cefetamet are independent of the dose. The absolute bioavailability of cefetamet tablets following oral cefetamet pivoxil administration is enhanced by the presence of food. Under fed conditions, 50 to 60% of the final oral dose is absorbed into the systemic circulation. This food effect is observed when cefetamet pivoxil is administered within 1 hour of a meal. Food also produces a slight delay in the time to reach peak plasma concentrations of this drug. Changes in fluid volume intake with cefetamet pivoxil administration have no effect on the bioavailability of this drug. Similar absorption characteristics have been observed for all of the tablet dosage formulations studied during clinical development. The absolute bioavailability of the final syrup dosage formulation was between 38 and 47%. Little improvement in the bioavailability of this preparation has been observed with food. The absorption and disposition of cefetamet in human subpopulations [i.e. children, elderly (< 75 years of age), renal impairment, liver disease and patients taking concomitant drugs] have been studied extensively. Only impaired renal function appears to significantly alter the elimination of this drug.(ABSTRACT TRUNCATED AT 400 WORDS)

Loracarbef. A review of its antimicrobial activity, pharmacokinetic properties and therapeutic efficacy

Loracarbef is an orally administered member of a new synthetic class of beta-lactam antibiotics, the carbacephems, which is characterised by enhanced chemical stability. At low concentrations (< 2 mg/L) in vitro, it inhibits Streptococcus pneumoniae, S. pyogenes, beta-haemolytic streptococci groups B, C and G. Proteus mirabilis and Moraxella catarrhalis, including beta-lactamase-producing strains. At therapeutic plasma concentrations it is also active in vitro against most strains of Staphylococcus aureus, S. saprophyticus, Escherichia coli and beta-lactamase-positive and -negative strains of Haemophilus influenzae. Like other beta-lactams, loracarbef is inactive against methicillin-resistant strains of S. aureus. When administered at dosages of 200 to 400 mg twice daily, the clinical and bacteriological efficacy of loracarbef is comparable with that of amoxicillin and amoxicillin/clavulanic acid in patients with upper or lower respiratory tract infections, and comparable with that of cefaclor in treating infections of the lower respiratory tract, skin and skin structures and urinary tract. Loracarbef and phenoxymethylpenicillin (penicillin V) were equally effective in treating streptococcal pharyngitis and tonsillitis. Loracarbef is generally well tolerated by all age groups and causes less diarrhoea than amoxicillin/clavulanic acid. It is administered twice daily. It offers a suitable alternative to other orally administered antibiotics for the treatment of mild to moderate infections caused by susceptible organisms.

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

Cefetamet pivoxil is an oral third-generation cephalosporin which is hydrolysed to form the active agent, cefetamet. Cefetamet has excellent in vitro activity against the major respiratory pathogens Streptococcus pneumoniae, Haemophilus influenzae, Moraxella (Branhamella) catarrhalis and group A beta-haemolytic streptococci; it is active against beta-lactamase-producing strains of H. influenzae and M. catarrhalis, but has poor activity against penicillin-resistant S. pneumoniae. Cefetamet has marked activity against Neisseria gonorrhoeae and possesses a broad spectrum of activity against Enterobacteriaceae. Both staphylococci and Pseudomonas spp. are resistant to cefetamet. Cefetamet pivoxil has been investigated in the treatment of both upper and lower community-acquired respiratory tract infections and has demonstrated equivalent efficacy to a number of more established agents, namely cefaclor, amoxicillin and cefixime. In patients with group A beta-haemolytic streptococcal pharyngotonsillitis, a 7-day course of cefetamet pivoxil was as effective as a 10-day course of the standard agent, phenoxymethylpenicillin, in this indication. In complicated urinary tract infections, cefetamet pivoxil showed similar efficacy to cefadroxil, cefaclor and cefuroxime axetil. Cefetamet pivoxil was effective in the treatment of otitis media, pneumonia, pharyngotonsillitis and urinary tract infections in children. Preliminary data indicate that single dose cefetamet pivoxil can effectively eradicate N. gonorrhoeae from both men and women. Cefetamet pivoxil has a tolerability profile similar to that of other oral cephalosporins, with gastrointestinal effects being the most commonly reported adverse events. To date, no symptoms of carnitine deficiency have been reported with cefetamet pivoxil. Cefetamet pivoxil offers effective alternative oral therapy for outpatient treatment of community-acquired respiratory tract infections, with the advantage of improved activity against H. influenzae and increased beta-lactamase stability. However, its use in areas with a high incidence of penicillin-resistant S. pneumoniae is likely to be limited. Cefetamet pivoxil is also effective in the treatment of urinary tract infections, although further trials are required to define any comparative advantages over other oral agents.

Antibacterial properties of Ro 40-6890, a broad-spectrum cephalosporin, and its novel orally absorbable ester, Ro 41-3399

Ro 41-3399 is a novel orally active ester of Ro 40-6890, an aminothiazolyl cephalosporin with potent in vitro activities against commonly encountered aerobic gram-positive bacteria (streptococci and methicillin-susceptible staphylococci) and gram-negative bacteria (members of the family Enterobacteriaceae, haemophili, meningococci, and gonococci). In terms of the MICs determined by the methods recommended by the National Committee for Clinical Laboratory Standards, for 50 and 90% of gram-positive organisms, the water-soluble free carboxylic acid Ro 40-6890 proved to be at least as active as or two- to fourfold more active than cefpodoxime, cefuroxime, cefaclor, amoxicillin, amoxicillin-clavulanic acid, and ceftriaxone; against aerobic gram-negative organisms, Ro 40-6890 was usually two- to fourfold more active than cefpodoxime, the next most potent of the oral drugs under comparison, but remained usually two- to fourfold weaker than ceftriaxone. Ro 40-6890 showed a high affinity for the essential penicillin-binding proteins of susceptible bacteria and was resistant to hydrolysis by a broad array of beta-lactamases. Ro 41-3399 bopentil was well absorbed in mice when administered by oral gavage and proved effective in several experimental bacterial infections. Further studies with Ro 41-3399 and Ro 40-6890 are in progress.

Effectiveness of cefetamet pivoxil in the treatment of pyelonephritis in children

Cefetamet pivoxil was investigated in an open, randomized comparative study involving a total of 37 children with acute pyelonephritis, whose ages ranged from 2 to 14 years. The patients received either 10 mg/kg (n = 18) or 20 mg/kg (n = 8) cefetamet pivoxil twice daily, or 30-50 mg/kg amoxycillin/clavulanic acid three times daily (n = 11) for a period of 7-10 days. Escherichia coli was the main causative agent isolated in 28 (75.7%) of the patients; other pathogens included Proteus mirabilis (three patients). Proteus species (one patient), Klebsiella pneumoniae (two patients), Pseudomonas diminuta (one patient) and mixed infections (three patients). No differences in the overall treatment outcome could be observed between the treatment regimens used and, at the end of treatment, all pathogens were eradicated with neither relapse, nor persistence of the isolated pathogen, nor reinfection occurring. The clinical signs and symptoms had subsided in all patients at treatment end and the tolerability of the trial drugs was found to be satisfactory with no premature treatment withdrawal required. It is concluded that cefetamet pivoxil in the standard twice-daily dose of 10 mg/kg was equally effective and as well tolerated as 20 mg/kg cefetamet pivoxil given twice daily or 30-50 mg/kg amoxycillin/clavulanic acid given three times daily.

In vitro activity of cefcanel versus other oral cephalosporins

Cefcanel is a new orally absorbed cephalosporin. Its activity was compared with that of cefuroxime, cefaclor, cephalexin, and cefixime against gram-positive and negative aerobic and anaerobic bacteria. Cefcanel had excellent activity against methicillin-susceptible Staphylococcus aureus and Staphylococcus epidermidis, MIC90 1 micrograms/ml, superior to the other oral cephalosporins. However, methicillin-resistant staphylococci were resistant, MIC greater than or equal to 16 micrograms/ml. Streptococcus pyogenes and Streptococcus pneumoniae were inhibited by 0.015-1 micrograms/ml, concentrations comparable to other cephalosporins. Clostridium spp. were inhibited by 0.25 micrograms/ml, 8- to 128-fold lower concentrations than were found for other agents, but the MICs were greater than 64 micrograms/ml for Bacteroides spp. The MIC90 for Moraxella catarrhalis was 1 micrograms/ml, similar to cefuroxime but 16-fold greater than the MICs of cefixime. Escherichia coli and Klebsiella pneumonia which were high beta-lactamase producers were resistant, MICs greater than 64 micrograms/ml, and 50% of Enterobacter cloacae and Citrobacter freundii were resistant. Cefcanel was hydrolyzed by TEM-1, TEM-3 and Moraxella Bro-1 beta-lactamases. Escherichia coli containing TEM-1, 2, 3, 5, 7, and 9 had cefcanel MICs of greater than or equal to 16 micrograms/ml. Although cefcanel inhibited gram-positive species as well as or at lower concentrations than other cephalosporins, it lacked activity against gram-negative species that produced common plasmid beta-lactamase although it inhibited Haemophilus influenzae carrying TEM-1.