L-627, a novel carbapenem: in-vitro activity against anaerobes

In vitro activity of Biapenem plus RPX7009, a carbapenem combined with a serine β-lactamase inhibitor, against anaerobic bacteria

Biapenem is a carbapenem being developed in combination with RPX7009, a new inhibitor of serine β-lactamases. Biapenem was tested alone and in combination with fixed concentrations of RPX7009 by agar dilution against 377 recent isolates of anaerobes. A separate panel of 27 isolates of Bacteroides spp. with decreased susceptibility or resistance to imipenem was also tested. Comparator drugs included meropenem, piperacillin-tazobactam, ampicillin-sulbactam, cefoxitin, ceftazidime, metronidazole, clindamycin, and tigecycline plus imipenem, doripenem, and ertapenem for the 27 selected strains. For recent consecutive strains of Bacteroides species, the MIC(90) for biapenem-RPX7009 was 1 μg/ml, with a MIC(90) of 4 μg/ml for meropenem. Other Bacteroides fragilis group species showed a MIC90 of 0.5 μg/ml for both agents. The MIC(90)s for biapenem-RPX7009 were 0.25 μg/ml for Prevotella spp., 0.125 μg/ml for Fusobacterium nucleatum and Fusobacterium necrophorum, 2 μg/ml for Fusobacterium mortiferum, 0.5 μg/ml for Fusobacterium varium, ≤ 0.5 μg/ml for Gram-positive cocci and rods, and 0.03 to 8 μg/ml for clostridia. Against 5 B. fragilis strains harboring a known metallo-beta-lactamase, biapenem-RPX7009 MICs were comparable to those of other carbapenems (≥ 32 μg/ml). Against Bacteroides strains with an imipenem MIC of 2 μg/ml, biapenem-RPX7009 had MICs of 0.5 to 2 μg/ml, with MICs of 0.5 to 32 μg/ml for meropenem, doripenem, and ertapenem. For strains with an imipenem MIC of 4 μg/ml, the MICs for biapenem-RPX7009 were 4 to 16 μg/ml, with MICs of 8 to >32 μg/ml for meropenem, doripenem, and ertapenem. The inhibitor RPX7009 had no antimicrobial activity when tested alone, and it showed little or no potentiation of biapenem versus anaerobes. Biapenem-RPX7009 showed activity comparable to that of imipenem and was superior to meropenem, doripenem, and ertapenem against imipenem-nonsusceptible Bacteroides spp.

Biapenem

Biapenem is a new parenteral carbapenem antibacterial agent with a broad spectrum of in vitro antibacterial activity encompassing many Gram-negative and Gram-positive aerobic and anaerobic bacteria, including species producing beta-lactamases. Biapenem is more stable than imipenem, meropenem and panipenem to hydrolysis by human renal dihydropeptidase-I (DHP-I), and therefore does not require the coadministration of a DHP-I inhibitor. After intravenous administration, biapenem is widely distributed and penetrates well into various tissues (e.g. lung tissue) and body fluids (e.g. sputum, pleural effusion, abdominal cavity fluid). In randomised, nonblind or double-blind clinical trials, biapenem showed good clinical and bacteriological efficacy (similar to that of imipenem/ cilastatin) in the treatment of adult patients with intra-abdominal infections, lower respiratory infections or complicated urinary tract infections. Biapenem is generally well tolerated. The most common adverse events in clinical trials were skin eruptions/rashes, nausea and diarrhoea.

Anti-anaerobic activity of antibacterial agents

The first very effective bactericidal anti-anaerobic drug was metronidazole, introduced in clinical practice in the early 1980s. Sometimes penicillin G and chloramphenicol were used successfully in some anaerobic infections. However, this result was most likely due to Gram-positive anaerobic infections (e.g., Clostridium perfringens). Very rapidly, the anti-anaerobic armamentarium was extended with clindamycin, cefoxitin, imipenem and co-amoxyclav or piperacillin-tazobactam. The resistance rate to metronidazole and imipenem remains low but clindamycin has seen an importance decrease in bacterial susceptibility. New additional drugs could be very helpful to overcome resistance and adverse events. The novelties in this field are fluoroquinolones, which exhibit a good activity against Gram-positive cocci and anaerobes.

Imipenem/cilastatin: an update of its antibacterial activity, pharmacokinetics and therapeutic efficacy in the treatment of serious infections

The prototype carbapenem antibacterial agent imipenem has a very broad spectrum of antibacterial activity, encompassing most Gram-negative and Gram-positive aerobes and anaerobes, including most beta-lactamase-producing species. It is coadministered with a renal dehydropeptidase inhibitor, cilastatin, in order to prevent its renal metabolism in clinical use. Extensive clinical experience gained with imipenem/cilastatin has shown it to provide effective monotherapy for septicaemia, neutropenic fever, and intra-abdominal, lower respiratory tract, genitourinary, gynaecological, skin and soft tissues, and bone and joint infections. In these indications, imipenem/cilastatin generally exhibits similar efficacy to broad-spectrum cephalosporins and other carbapenems and is at least equivalent to standard aminoglycoside-based and other combination regimens. Imipenem/cilastatin is generally well tolerated by adults and children, with local injection site events, gastrointestinal disturbances and dermatological reactions being the most common adverse events. Seizures have also been reported, occurring mostly in patients with impaired renal function or CNS pathology, or with excessive dosage. Although it is no longer a unique compound, as newer carbapenems such as meropenem are becoming available, imipenem/cilastatin nevertheless remains an important agent with established efficacy as monotherapy for moderate to severe bacterial infections. Its particular niche is in treating infections known or suspected to be caused by multiresistant pathogens.