AmBisome: relationship between the pharmacokinetic characteristics acquired by liposomal formulation and safety/efficacy.

Amphotericin B (AMPH-B) is a polyene antifungal agent with a superior and broad fungicidal spectrum, but its administration at a dose sufficient for treatment is difficult because of dose- and duration-dependent nephrotoxicity. To solve this dilemma, a liposomal formation of AMPH-B that achieved reduction of adverse effects while maintaining the efficacy, AmBisome® (L-AMB), was developed. In L-AMB, AMPH-B molecules are stabilized by phospholipids and cholesterol in the liposomal lipid bilayer, reducing the cytotoxicity for animal cells compared with that of the free-form AMPH-B. In addition, extravascular permeation of L-AMB is limited in normal tissue because of the liposome particle size (particle diameter: 100 nm or smaller), a high blood level is maintained and the distribution in organs, including the kidney is reduced, contributing to the improvement of the safety. On the other hand, vascular permeation increases due to inflammation and damage by fungal invasion, which increases L-AMB transfer from the circulation to lesions and its antifungal activity. Furthermore, since the parameter most closely correlated with the in vivo outcome of L-AMB is Cmax/MIC, the pharmacokinetic (PK) characteristics of L-AMB, which result in a high blood level than that for the free-form AMPH-B, is advantageous for antifungal activity. Incorporation of AMPH-B into the liposomal membrane resulted in PK characteristics of L-AMB markedly different from those of AMPH-B, and the superior efficacy and safety were achieved based on these characteristics. In this review, the relationship between the PK characteristics of L-AMB and safety/efficacy is introduced.

Therapeutic effect of meropenem on an experimental guinea pig model of meningitis with type b ß-lactamase-nonproducing ampicillin-resistant Haemophilus influenzae.

The purpose of this study was to investigate the relationship between efficacy and percentage of time above the MIC (%T>MIC) in the cerebrospinal fluid (CSF) for different dosing regimens of meropenem against an experimental lethal meningitis model in guinea pigs with type b ß-lactamase-nonproducing ampicillin-resistant Haemophilus influenzae (Hib BLNAR). Guinea pigs were intrathecally inoculated with 10(8) CFU/head of Hib BLNAR 8 h before the start of therapy. A single dose of 20, 40, or 80 mg/kg meropenem or multiple doses of 40 mg/kg meropenem were subcutaneously administered. Numbers of bacteria in CSF were counted 8 h after the start of therapy. Meropenem concentration in serum and CSF were determined in infected guinea pigs receiving a single dose of 40 mg/kg. In the single-dose regimen, 40 and 80 mg/kg meropenem significantly reduced the number of bacteria in CSF compared with the control, but 20 mg/kg meropenem did not. The %T>MIC for an 8-h period of 20, 40, and 80 mg/kg meropenem were 41, 52, and 62, respectively. Two and four doses of 40 mg/kg meropenem, for both of which %T>MIC was calculated as 100, had similar efficacy and were significantly superior to a single-dose of 40 mg/kg. In conclusion, meropenem had high efficacy when %T>MIC in the CSF was increased because of the high dose level and shortening of the dosing interval in a guinea pig meningitis model caused by Hib BLNAR, suggesting that high and frequent doses of meropenem are useful for treatment of meningitis with Hib BLNAR.

Novel carbapenem antibiotics for parenteral and oral applications: in vitro and in vivo activities of 2-aryl carbapenems and their pharmacokinetics in laboratory animals.

SM-295291 and SM-369926 are new parenteral 2-aryl carbapenems with strong activity against major causative pathogens of community-acquired infections such as methicillin-susceptible Staphylococcus aureus, Streptococcus pneumoniae (including penicillin-resistant strains), Streptococcus pyogenes, Enterococcus faecalis, Klebsiella pneumoniae, Moraxella catarrhalis, Haemophilus influenzae (including ß-lactamase-negative ampicillin-resistant strains), and Neisseria gonorrhoeae (including ciprofloxacin-resistant strains), with MIC(90)s of ≤ 1 µg/ml. Unlike tebipenem (MIC(50), 8 µg/ml), SM-295291 and SM-369926 had no activity against hospital pathogens such as Pseudomonas aeruginosa (MIC(50), ≥ 128 µg/ml). The bactericidal activities of SM-295291 and SM-369926 against penicillin-resistant S. pneumoniae and ß-lactamase-negative ampicillin-resistant H. influenzae were equal or superior to that of tebipenem and greater than that of cefditoren. The therapeutic efficacies of intravenous administrations of SM-295291 and SM-369926 against experimentally induced infections in mice caused by penicillin-resistant S. pneumoniae and ß-lactamase-negative ampicillin-resistant H. influenzae were equal or superior to that of tebipenem and greater than that of cefditoren, respectively, reflecting their in vitro activities. SM-295291 and SM-369926 showed intravenous pharmacokinetics similar to those of meropenem in terms of half-life in monkeys (0.4 h) and were stable against human dehydropeptidase I. SM-368589 and SM-375769, which are medoxomil esters of SM-295291 and SM-369926, respectively, showed good oral bioavailability in rats, dogs, and monkeys (4.2 to 62.3%). Thus, 2-aryl carbapenems are promising candidates that show an ideal broad spectrum for the treatment of community-acquired infections, including infections caused by penicillin-resistant S. pneumoniae and ß-lactamase-negative ampicillin-resistant H. influenzae, have low selective pressure on antipseudomonal carbapenem-resistant nosocomial pathogens, and allow parenteral, oral, and switch therapies.

Influence of fungicidal activity against Candida tropicalis on the efficacy of micafungin and liposomal amphotericin B in a neutropenic murine lethal infection model.

OBJECTIVES: To investigate the correlation between in vitro killing activity and in vivo efficacy of micafungin (MCFG) and liposomal amphotericin B (L-AMB) against Candida tropicalis in a neutropenic murine lethal infection model. METHODS: Candida albicans (one strain) and C. tropicalis (three strains) were tested in time-kill studies. Cyclophosphamide-treated mice were inoculated intravenously with each strain. One day after inoculation, antifungals were administered intravenously once daily for 1 or 3 days. RESULTS: MCFG exhibited fungicidal activity against C. albicans ATCC 90029 and C. tropicalis SP-20142, and fungistatic activity against C. tropicalis ATCC 42678 and SP-20047. The ED(50)s (dosage that results in 50% survival) of MCFG for C. tropicalis ATCC 42678 and SP-20047 (4.1-50 mg/kg) were higher than those for other strains (1.6-12 mg/kg). A 1-day course of MCFG was not effective against C. tropicalis ATCC 42678 and SP-20047 at the clinical dose (5 mg/kg), which achieved an AUC level almost equal to that of 100 mg in humans, whereas a 3-day course of 5 mg/kg MCFG was efficacious against all strains. In contrast, L-AMB showed fungicidal activity against all strains tested and the ED(50)s of L-AMB were 0.08-0.65 mg/kg. In both treatment regimens, the minimum effective doses of L-AMB (≤0.5 mg/kg) were less than the clinical dosage (≤5 mg/kg). CONCLUSIONS: The in vivo efficacy of MCFG and L-AMB showed a correlation with the in vitro killing activity. At the clinical dose, L-AMB exerted anti-C. tropicalis activity within a shorter treatment period than MCFG.

[In vivo activity of liposomal amphotericin B against Exophiala dermatitidis in a murine lethal infection model].

This study evaluated the in vivo activity of liposomal amphotericin B (L-AMB) and deoxycholate amphotericin B (D-AMB) in a murine model of disseminated infection caused by Exophiala dermatitidis. Cyclophosphamide-treated neutropenic ddY mice were inoculated intravenously with conidial suspensions of E. dermatitidis IFM 4827 or IFM 53409. The maximum tolerated doses of L-AMB and D-AMB were set at 10 mg/kg and 1 mg/kg, respectively. Four hours after infection, a single dose of L-AMB (0.3 to 10 mg/kg) or D-AMB (0.1 to 1 mg/kg) was administered intravenously. The efficacy of the antifungal treatment was assessed by the survival time over two weeks and the tissue fungal burdens 4 days after infection. L-AMB at a dose of > or =1 mg/kg significantly prolonged the survival time of mice infected with either strain compared with that of the control group. Percent survivals in the 10 mg/kg L-AMB-treated group (100% and 75%) were higher than those in the 1 mg/kg D-AMB-treated group (20% and 37.5%) in the IFM 4827 and IFM 53409 models, respectively. In the IFM 4827 model, 10 mg/kg L-AMB exhibited greater efficacy than 1 mg/kg D-AMB in terms of reducing the tissue fungal burdens (blood, lung, liver, spleen, and kidneys). These findings suggest that L-AMB was effective in the treatment of experimental disseminated E. dermatitidis infection, and the efficacy of L-AMB was superior to that of D-AMB.

Comparative study of the efficacy of liposomal amphotericin B and amphotericin B deoxycholate against six species of Zygomycetes in a murine lethal infection model.

The objective of this study was to investigate the efficacy of liposomal amphotericin B (L-AMB) at a clinical dose (3 mg/kg) against six species (5 genera) of Zygomycetes in a murine lethal infection model, and to compare findings with those for deoxycholate amphotericin B (D-AMB). The correlation between in-vitro activity and in-vivo efficacy of L-AMB was also investigated. Cyclophosphamide-treated mice were inoculated intravenously with conidial suspensions. Four hours or 1 day after inoculation, a single dose of L-AMB or D-AMB was administered intravenously. The number of mice that survived for 14 days was recorded. L-AMB at a dose of at least ≥1 mg/kg significantly prolonged the survival time of infected mice compared with the control group. The ED50 of L-AMB was nearly equivalent to that of D-AMB, except for the treatment initiated on day 1 in the Rhizopus oryzae model. At the maximum tolerated dose (MTD) of each agent, survival percentages with L-AMB (10 mg/kg) were equal to or higher than those with D-AMB (1 mg/kg). The ED50 of L-AMB decreased as the MIC against the infecting strain decreased. In conclusion, L-AMB was effective at a clinical dosage, and at the MTD the efficacy of L-AMB was equal or superior to that of D-AMB in a murine model of disseminated zygomycosis. The in-vivo activity of L-AMB was correlated with its in-vitro activity.

Experimental verification of the efficacy of optimized two-step infusion therapy with meropenem using an in vitro pharmacodynamic model and Monte Carlo simulation.

In this study we compared the efficacy of a theoretically optimized two-step infusion therapy (OTIT; rapid first-step infusion and slow second-step infusion) to the efficacies of prolonged infusion therapy (PIT) and traditional 0.5 h infusion therapy (TIT) with meropenem against Pseudomonas aeruginosa using an in vitro pharmacodynamic model and a Monte Carlo simulation. In the in vitro pharmacodynamic model, the bactericidal effect against P. aeruginosa was evaluated for 8 h, which is the usual dosing interval of meropenem. It was confirmed that the durability of the bactericidal effect of OTIT (0.25-1 g/0.5 h + 0.25-1 g/4 h t.i.d.) was almost equal to that of PIT and superior to that of TIT (0.5-2 g/0.5-4 h t.i.d.). In addition, the initial bactericidal effects of OTIT were superior to those of the prolonged 4 h infusion. In the Monte Carlo simulation study, the probability of target attainments (PTAs) of all dosing regimens of OTIT at MICs of 2-8 µg/ml were apparently superior to those of TIT and 4- and 6 h-PIT, when the target therapeutic condition for serious life-threatening infections was the achievement of both the percentage of the dosing interval at which the drug concentration exceeds the MIC (%T(>MIC)) ≥ 50% and the peak level divided by the MIC (Cmax/MIC) ≥ 4. Especially, the PTAs of the dosing regimens of 0.25-1 g/0.5 h + 0.25-1 g/4-6 h were excellent at MICs of 2-8 µg/ml. Against recent clinical isolates of P. aeruginosa in Japan, the dosing regimens of OTIT provided higher PTAs compared with those of TIT and 4- and 6 h-PIT. These results suggested that OTIT with sufficient pharmacokinetic conditions could be useful for enhancing the therapeutic efficacy of meropenem against serious life-threatening infections.

Pharmacodynamics of SMP-601 (PTZ601) against vancomycin-resistant Enterococcus faecium and methicillin-resistant Staphylococcus aureus in neutropenic murine thigh infection models.

SMP-601 (also known as PTZ601, PZ-601, or SM-216601) is a novel parenteral carbapenem with potent activity against multidrug-resistant gram-positive pathogens, including vancomycin-resistant Enterococcus faecium (VREF) and methicillin-resistant Staphylococcus aureus (MRSA). The pharmacodynamics of SMP-601 against VREF and MRSA were investigated in neutropenic murine thigh infection models. The percentage of the dosing interval that the unbound SMP-601 concentration exceeded the MIC (f%T>MIC) was the pharmacokinetic-pharmacodynamic parameter that correlated most closely with efficacy with R(2) values of 0.81 to 0.84 for two strains of VREF and 0.92 to 0.93 for two strains of MRSA, whereas the R(2) values for the area under the concentration-time curve from 0 to 24 h divided by the MIC were 0.12 to 0.89, and the R(2) values for the peak level divided by the MIC were 0 to 0.22. The f%T>MIC levels required for static or killing efficacy against two strains of VREF (9 to 19%) apparently were lower than those against two strains of MRSA (23 to 37%). These results suggested that SMP-601 showed time-dependent in vivo efficacy against VREF and MRSA, and SMP-601 had a sufficient therapeutic effect against VREF infections at lower exposure conditions compared to those for with MRSA infections.

Comparative study on the efficacy of liposomal amphotericin B and voriconazole in a murine pulmonary aspergillosis model.

BACKGROUND: No clinical studies have compared the efficacy of liposomal formulation AMB (L-AMB) and voriconazole (VRC) in the treatment of pulmonary aspergillosis. The aim of this study was to compare the efficacy of L-AMB and VRC in murine pulmonary aspergillosis. METHODS: Leucopenic mice were infected intratracheally with Aspergillus fumigatus and treated intravenously with L-AMB (once a day) or VRC (twice a day). RESULTS: L-AMB and VRC at a dose of >or=5 and >or=20 mg/kg, respectively, significantly prolonged the survival time of infected mice and reduced the pulmonary fungal burden in comparison with the control group. At the maximum recommended dose for clinical use, 5 mg/kg of L-AMB exhibited greater efficacy than 10 mg/kg of VRC, which achieved an area under the concentration-time curve level equivalent to that of 6 mg/kg (loading dose) in humans, in terms of increasing survival and reducing the fungal burden. CONCLUSION: The in vivo efficacy of L-AMB was superior to that of VRC at the maximum recommended dose in a murine pulmonary aspergillosis model.

The mode of action of 2-(thiazol-2-ylthio)-1beta-methylcarbapenems against Pseudomonas aeruginosa: the impact of outer membrane permeability and the contribution of MexAB-OprM efflux system.

The mode of action of a series of 2-(4-dihydropyrrolylthiazol-2-ylthio) and 2-(4-tetrahydropyridinylthiazol-2-ylthio)-1beta-methylcarbapenem analogues against Pseudomonas aeruginosa was investigated with regard to contributions of the affinity for penicillin binding proteins (PBPs), the outer membrane permeability, and the effect of the MexAB-OprM efflux system. In this series of carbapenems, the introduction of a substituent in C-2 side chain with a change in physicochemical properties affected the antipseudomonal activity depending on the molecular weight. However, these structural modifications did not affect the affinity for pseudomonal PBPs significantly. It was confirmed that the affinity for PBPs was not an important determinant of the antipseudomonal activity of this series of carbapenems. OprD porin-deficiency did not affect antipseudomonal activity either. On the other hand, the MIC of these carbapenems against P. aeruginosa significantly decreased in the presence of outer membrane permeabilizer. This result strongly suggests that the cause of the relatively low antipseudomonal activity of these carbapanems is their low permeability through the outer membrane of P. aeruginosa. And also, in the presence of outer membrane permeabilizer, the MICs against MexAB-OprM deficient mutants remarkably decreased and were very close to the value of the IC(50) for pseudomonal PBPs. From this result, it was clear that the effect of the MexAB-OprM efflux system was also an important determinant of antipseudomonal activity of these carbapenems. In conclusion, the major determinants of the antipseudomonal activity of the 2-(thiazol-2-ylthio)-1beta-methylcarbapenems are the outer membrane permeability and the effect of the MexAB-OprM efflux system, not the affinity for pseudomonal PBPs.

In vitro and in vivo antibacterial activities of SM-216601, a new broad-spectrum parenteral carbapenem.

SM-216601 is a novel parenteral 1beta-methylcarbapenem. In agar dilution susceptibility testing, the MIC of SM-216601 for 90% of the methicillin-resistant Staphylococcus aureus (MRSA) strains tested (MIC(90)) was 2 microg/ml, which was comparable to those of vancomycin and linezolid. SM-216601 was also very potent against Enterococcus faecium, including vancomycin-resistant strains (MIC(90) = 8 microg/ml). SM-216601 exhibited potent activity against penicillin-resistant Streptococcus pneumoniae, ampicillin-resistant Haemophilus influenzae, Moraxella catarrhalis, Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis, with MIC(90)s of less than 0.5 microg/ml, and intermediate activity against Citrobacter freundii, Enterobacter cloacae, Serratia marcescens, and Pseudomonas aeruginosa. The therapeutic efficacy of SM-216601 against experimentally induced infections in mice caused by S. aureus, E. faecium, E. coli, and P. aeruginosa reflected its in vitro activity and plasma level. Thus, SM-216601 is a promising candidate for nosocomial bacterial infections caused by a wide range of gram-positive and gram-negative bacteria, including multiresistant pathogens.

[In vitro combined effect of meropenem and various antimicrobial agents against beta-lactamase-nonproducing ampicillin-resistant Haemophilus influenzae and penicillin-resistant Streptococcus pneumoniae].

As a basic study of combination therapy for bacterial meningitis, in vitro combined effect of meropenem (MEPM) and various antimicrobial agents against beta-lactamase-nonproducing ampicillin-resistant Haemophilus influenzae (BLNAR) and penicillin-resistant Streptococcus pneumoniae (PRSP) was investigated. The following findings were obtained. 1. In the checker board assay using 23 clinical isolates of BLNAR, MEPM+cefotaxime (CTX), MEPM+ampicillin (ABPC), and MEPM+rifampicin (RFP) showed synergistic effect (21 strains, 6 strains, 4 strains, respectively) or additive effect (2 strains, 17 strains, 19 strains, respectively). 2. In the checker board assay using 19 clinical isolates of PRSP, MEPM+CTX, MEPM+teicoplanin (TEIC), and MEPM+RFP showed synergistic effect (5 strains, 8 strains, 1 strain, respectively), additive effect (14 strains, 11 strains, 17 strains, respectively) or indifference (0 strain, 0 strain, 1 strain, respectively). 3. The time-kill assay with BLNAR demonstrated synergistic bactericidal effect of MEPM+CTX and MEPM+RFP, but not MEPM+ABPC. 4. The time-kill assay with PRSP demonstrated synergistic or additive bactericidal effect of MEPM+CTX, MEPM+TEIC, and MEPM+RFP. 5. There were no antagonistic effect in any combination tested in this study. These findings suggest that combination therapy with MEPM and various antimicrobial agents tested in this study are useful in treating bacterial meningitis caused by BLNAR and PRSP.

Orally active carbapenem antibiotics I. Antibacterial and pharmacokinetic potential of 2-phenyl and 2-thienylcarbapenems.

In order to design orally active carbapenem antibiotics effective against beta-lactam-resistant pathogens, such as penicillin-resistant Streptococcus pneumoniae (PRSP) and beta-lactamase non-producing ampicillin-resistant Haemophilus influenzae (BLNAR), a series of novel 2-phenylcarbapenems and some 2-thienyl derivatives were synthesized and tested for antibacterial activities. These compounds were highly active against PRSP, BLNAR, and major Gram-positive and Gram-negative bacteria that cause community-acquired infections. Their pivaloyloxymethylester-type prodrug exhibited good oral absorption in mice, suggesting that this series of carbapenems were promising as a prototype of novel orally active beta-lactams.

[Bactericial activity of chlorhexidine gluconate against recent clinical isolates of various bacterial species in Japan].

The minimum inhibitory concentration (MIC) and bactericidal activity of chlorhexidine gluconate (CHG) were determined for methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), Escherichia coli, Serratia marcescens, Eterobacter cloacae, Pseudomonas aeruginosa and Burkholderia cepacia, isolated from patients in medical institutions all over Japan between 2000 and 2002. The following findings were obtained. 1. The MICs of CHG against MSSA, MRSA, E. coli and B. cepacia were 0.002% or less, and those against S. marcescens, E. cloacae and P. aeruginosa were 0.008% or less. 2. Rapid and strong bactericidal effects of CHG were observed against all clinical isolates of E. coli, E. cloacae and P. aeruginosa tested even at relatively low concentrations (0.02 to 0.05%). 3. Relatively high concentration or prolonged treatment time was required to achieve sufficient bactericidal effect of CHG against some isolates of S. aureus, S. marcescens and B. cepacia. These results suggest that CHG is useful antiseptic agent or disinfectant for recent clinical isolates of various bacterial pathogens. In addition, the selection of treatment concentration and treatment time for each organism and purpose was important to obtain sufficient bactericidal effect.