The differences between the antibacterial activities of new macrolides such as clarithromycin (CLA) and azithromycin (AZI) against common respiratory tract pathogens are only minor. However, CLA and AZI constitute macrolides with extremely different pharmacokinetic profiles. This constellation presents an opportunity to evaluate the effect of the pharmacokinetic profile on antibacterial kinetics comparatively. In a pharmacodynamic model simulating the dynamics of serum concentrations in bacterial cultures, both CLA and AZI demonstrate bactericidal activity at concentrations reached in human blood at recommended dosages (CLA 250 mg b.i.d., AZI 500 mg o.i.d.). Bactericidal activity of CLA against the variety of pathogens included is superior to that of AZI in the rate and the extent of killing in this model. These results are considered to correlate with the antibacterial effect of macrolidesin vivo in cases where pathogens enter the blood stream. Furthermore, mutants with susceptibility reduced between 8 and 16 times in relation to the initial strain of all strains having an initial minimal inhibitory concentration (MIC) ≤ 0.25 mg/l, are selected during exposure to AZI, but not to CLA. The pharmacokinetic profiles of CLA and AZI thus strongly influence their antibacterial effect in the pharmacodynamic model, allowing both higher bactericidal activity and greater reduction of the risk of selection of resistant mutants with CLA than with AZI. As a whole, the pharmacodynamics of these macrolides are determined more by the proportion of the MICs to the maximum serum concentration than by the relation of the MICs to the area under the curve.

The first outbreak of infections caused by an SHV-5 producing strain ofKlebsiella pneumoniae is reported. Within a period of 1 year and 9 months, multiresistantK. pneumoniae strains caused severe infections, mostly of the lower respiratory tract, in 22 patients. The strains were resistant to penicillins, third-generation cephalosporins, aztreonam, chloramphenicol, tetracycline and co-trimoxazole. The resistance determinants were transferable toEscherichia coli. All isolates produced a beta-lactamase with a pI of 8.2. Ceftazidime was hydrolyzed at this band. These characteristics, together with the resistance phenotype, are identical to those of a reference strain producing the beta-lactamase SHV-5. TheK. pneumoniae strains of all patients were identical in their capsular serotype (K1), plasmid pattern and plasmid fingerprint after digestion with Dra I restriction endonuclease. We conclude that this outbreak was caused by the spread of one clone ofK. pneumoniae producing SHV-5 beta-lactamase among patients of different wards. Our results indicate a real risk for failure of therapy by third-generation cephalosporins in intensive care patients due to SHV-5 producing pathogens.

The aminothiazolyl-cephalosporin RU 29 246 is the active metabolite of the prodrug pivaloyloxyethylester HR 916. RU 29 246 in vitro activity includes a wide range of clinically relevant bacterial pathogens. Against methicillin-sensitive Staphylococci RU 29 246 (MIC90 of 0.25 approximately 2-mu-g/ml) was clearly more active than cefaclor, cefuroxime, cefpodoxime, cefixime and ceftibuten, but slightly less active than cefdinir. RU 29 246 inhibited hemolytic Streptococci of the serogroups A, B, C and G as well as penicillin-sensitive Streptococcus pneumoniae at concentrations similar to cefdinir, cefpodoxime and cefuroxime (MIC90 less-than-or-equal-to 0.13-mu-g/ml), but less than the other oral cephaiospofins investigated (cefixime, cefaclor and ceftibuten). MIC90s of RU 29 246 against Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Salmonella spp., Shigella spp., Proteus mirabilis and Haemophilus influenzae were less-than-or-equal-to 0.5-mu-g/ml. Only RU 29 246 and cefdinir demonstrated moderate activity against Acinetobacter baumannii (MIC90 greater-than-or-equal-to 4-mu-g/ml). Most strains of Pseudomonas spp., Serratia marcescens, Enterobacter spp., Hafnia alvei and Bacteroides spp. were resistant to RU 29 246. RU 29 246 killed Escherichia coli and Staphylococcus aureus at a rate of 99% to 99.9% at concentrations of two times MIC. The pH value of the medium (range 5.5 to 8.5) and the inoculum size (range 10(5) to 10(7) cfu/ml) had no or only low influence on the antibacterial activity of RU 29 246. RU 29 246 is a broad spectrum cephalosporin including in its activity both Gram-positive and Gram-negative pathogens and therefore-depending on the bioavailability of its prodrug-looks promising as to its therapeutic perspective.

The aminothiazolyl-cephalosporin RU 29 246 is the active metabolite of the prodrug-pivaloyl-oxyethyl-ester HR 916. RU 29 246 in vitro activity includes a wide range of clinically relevant bacterial pathogens. Against methicillin-sensitive Staphylococci RU 29 246 (MIC90 of 0.25 approximately 2 micrograms/ml) was clearly more active than cefaclor, cefuroxime, cefpodoxime, cefixime and ceftibuten, but slightly less active than cefdinir. RU 29 246 inhibited hemolytic Streptococci of the serogroups A, B, C and G as well as penicillin-sensitive Streptococcus pneumoniae at concentrations similar to cefdinir, cefpodoxime and cefuroxime (MIC90 less than or equal to 0.13 micrograms/ml), but less than the other oral cephalosporins investigated (cefixime, cefaclor and ceftibuten). MIC90s of RU 29 246 against Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Salmonella spp., Shigella spp., Proteus mirabilis and Haemophilus influenzae were less than or equal to 0.5 micrograms/ml. Only RU 29 246 and cefdinir demonstrated moderate activity against Acinetobacter baumannii (MIC90 greater than or equal to 4 micrograms/ml). Most strains of Pseudomonas spp., Serratia marcescens, Enterobacter spp., Hafnia alvei and Bacteroides spp. were resistant to RU 29 246. RU 29 246 killed Escherichia coli and Staphylococcus aureus at a rate of 99% to 99.9% at concentrations of two times MIC. The pH value of the medium (range 5.5 to 8.5) and the inoculum size (range 10(5) to 10(7) cfu/ml) had no or only low influence on the antibacterial activity of RU 29 246. RU 29 246 is a broad spectrum cephalosporin including in its activity both Gram-positive and Gram-negative pathogens and therefore--depending on the bioavailability of its prodrug--looks promising as to its therapeutic perspective.

The therapeutic perspectives of flomoxef, SCE 2787, cefpirome, cefepime, latamoxef, cefotaxime and of piperacillin plus tazobactam were comparatively evaluated by theirin vitro activity against 1119 clinical isolates of 83 bacterial species.Escherichia coli, Klebsiella spp.Enterobacter sakazakii, Proteus spp. andShigella spp. were about equally susceptible to the cephalosporins (MIC90: 0.06 to 0.5 mg/l), while the MIC90 for piperacillin plus tazobactam was between 2 and 16 mg/l.Enterobacter cloacae, Enterobacter aerogenes andSerratia spp. were most susceptible to SCE 2787, cefpirome and cefepime (MIC90: 0.06 to 2 mg/l) followed by latamoxef, cefotaxime, flomoxef and piperacillin plus tazobactam. ForCitrobacter spp.,Providencia spp. andYersinia enterocolitica MIC90 were between 0.06 and 0.5 mg/l. Flomoxef was between 2 to 4 log2 less active against these species but more active than piperacillin plus tazobactam (MIC90: 2 and 8 mg/l).Morganella morganii andHafnia alvei were most susceptible to cefepime, cefpirome and latamoxef (MIC90: 0.13 to 0.5 mg/l) while cefotaxime (MIC90: 8 mg/l) and piperacillin plus tazobactam (MIC90: 8 and > 64 mg/l) were the least active compounds. SCE 2787, cefepime and cefpirome were the most potent beta-lactams against the majority of the 13 species of non-fermentative bacilli (NFB) investigated (MIC90: 0.5 to 16 mg/l). The oxacephems were the least active compounds against NFB. Cefepime was the most active of the compounds included againstPseudomonas aeruginosa (MIC90: 16 mg/l).Haemophilus spp.,Neisseria gonorrhoeae andBordetella pertussis were most susceptible to cefotaxime (MIC90: 0.03 to 0.06 mg/l). Latamoxef had the lowest activity of all compounds against gram-positive cocci. Flomoxef was the most active compound against penicillinase producingStaphylococcus aureus and about equally active as the other betalactams against methicillin susceptible staphylococci of other staphylococcal species. Non-enterococcal streptococci had MIC90 between 0.03 und 0.5 mg/l for all.Streptococcus pneumoniae with MICs for penicillin equal to or above 1 mg/l were between 16 and 64 times less susceptible (MIC90: between 0.5 and 4 mg/l) than penicillin-susceptible organisms (MIC90: between 0.03 and 0.13 mg/l). Flomoxef and piperacillin plus tazobactam were the most active of the compounds against anaerobic organisms. The oxacephem flomoxef was the most stable of the compounds included against novel extended broad spectrum beta-lactamases (TEM-3 to TEM-7, SHV-2 to SHV 5, CMY-1, CTX-M-1) followed by latamoxef. However, both oxacephamycins are hydrolysed by cephamycinases while SCE 2787, cefepime and cefpirome are stable against cephamycinases. Progress in antibacterial activity of parenteral cephalosporins was achieved both by structural modifications (of latamoxef or cefotaxime) and combination of piperacillin with taxobactam. Flomoxef in comparison with latamoxef extended its spectrum to include staphylococci and increased activity against non-enterococcal streptococci 16 to 32 times. The various structural modifications of cefotaxime at position 3 of the cephalosporin ring improved the antibacterial profile of SCE 2787, cefepime and cefpirome in very much the same way (enhanced activity mainly against organisms producing chromosomal cephalosporinases, e. g.Enterobacter spp.,Serratia spp.,H. alvei, M. morganii and non-fermentative bacilli). Tazobactam protects piperacillin against plasmidic beta-lactamases, however, this was achieved to an even higher extent by the structural modifications of aminothiazole-methoximino cephalosporins (SCE 2787, cefepime and cefpirome) and in particular of flomoxef.

From in-vitro data, recommendations for dosing with fleroxacin are presented. Serum pharmacokinetics of 250, 400, 500, 800, 1000 and 1500 mg once daily dosages were simulated in bacterial cultures. The bactericidal kinetics of clinical isolates of Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus with MICs for fleroxacin similar to MIC90 or above were investigated. Bacterial populations of all strains with MICs equal to or below 2 mg/l were reduced by at least 99% by a once daily dosage of 400 mg of fleroxacin. 500 mg once per day was high enough to induce a two log reduction of P. aeruginosa MIC 4 mg/l. At a 250 mg dosing mutants with MICs four times above the MICs of the initial strains were selected. The increased concentrations of fleroxacin after multiple dosing enhanced bactericidal activity. Once daily dosing increased the initial rate of killing but reduced the extent of inactivation in comparison with twice daily dosing of the same total amount. From our in-vitro investigation a once daily dosage of 400 mg of fleroxacin should be effective against causative organisms with an MIC of up to 2 mg/l, both in the rate and extent of killing and to minimize the risk for selection of resistant mutants.