The in vivo properties of pagoclone in rat are most likely mediated by 5′-hydroxy pagoclone

The cyclopyrrolone pagoclone binds with roughly equivalent high affinity (0.7-9.1nM) to the benzodiazepine binding site of human recombinant GABA(A) receptors containing either an alpha1, alpha2, alpha3 or alpha5 subunit. However, whereas it was a partial agonist at alpha1-, alpha2- and alpha5-containing GABA(A) receptors, pagoclone was a full agonist at receptors containing an alpha3 subunit. In the rat elevated plus maze assay pagoclone (3mg/kg) had significant anxiolytic-like activity but at all three doses tested (0.3, 1 and 3mg/kg p.o.) it produced a significant reduction in the total distance travelled. This sedative-like effect was confirmed in rat chain-pulling and spontaneous locomotor assays. Surprisingly, in the plasma and brain samples derived from the elevated plus maze assay, the major metabolite of pagoclone, 5'-hydroxy pagoclone, was present at 10-20-fold higher concentrations relative to the parent compound. In order to establish whether this metabolite might have pharmacological activity, we measured its affinity and efficacy profile and found that both were comparable to those of pagoclone with the exception that efficacy at the alpha1 subtype was considerably greater for 5'-hydroxy pagoclone compared with the parent. This metabolite had significant anxiolytic-like activity in the elevated plus maze but at these same doses (0.3-3mg/kg p.o.) also produced sedation. It is therefore likely that in rats 5'-hydroxy pagoclone mediates the majority of the pharmacological actions following pagoclone administration.

Different modes of action of naphthyridones in gram-positive and gram-negative bacteria

Naphthyridones that were recently described as a class of translation inhibitors in gram-positive bacteria mediate their mode of action via GyrA in Haemophilus influenzae and Escherichia coli. These are the first examples of compounds in which modes of action in different bacterial pathogens are mediated through widely different targets.

Pharmacodynamic evaluation of tosufloxacin against Streptococcus pneumoniae in an in vitro model simulating serum concentration

We compared the antibacterial effects and the emergence of resistance to tosufloxacin or levofloxacin for Streptococcus pneumoniae by simulating the serum concentration according to the Japanese clinical regimens using an in vitro pharmacokinetic-pharmacodynamic model. For quinolone-susceptible strain ATCC49619, tosufloxacin showed bactericidal activity, given that both the AUC(0-24h)/MIC ratios at the dosage of 150 mg t.i.d. and 300 mg b.i.d. of tosufloxacin tosilate were 138 and 193, and the C(max)/MIC ranges were 7.93-10.2 and 15.9-17.6, respectively, which were greater than those of levofloxacin (100 mg t.i.d. and 200 mg b.i.d.). The greater area above the killing curves (AAKCs) or shorter time to achieve 99.9% killing (99.9% KT) in both models of tosufloxacin than those of levofloxacin was related to their larger AUC(0-24h)/MIC and C(max)/MIC. Exposure of only 100 mg t.i.d. of levofloxacin led to outgrowth of the parC mutants, which were twofold less susceptible to levofloxacin than the parent strain. Neither of the tosufloxacin tosilate regimens resulted in isolation of resistant mutants of this strain. For the parC mutant strain D-3197, both the AUC(0-24h)/MIC and C(max)/MIC ratios of tosufloxacin were greater than those of levofloxacin, which resulted in comparable or better bactericidal activity as compared to those of levofloxacin. However, both fluoroquinolones and both regimens led to outgrowth of resistant mutants, which possessed a mutation in gyrA in addition to parC. In conclusion, tosufloxacin is superior to levofloxacin in bactericidal activity against S. pneumoniae in the Japanese clinical regimens, especially in the quinolone-susceptible strain, without emergence of resistant subpopulations.

A new and simple solid-phase extraction method for LC determination of pyronaridine in human plasma

A new approach using a simple solid-phase extraction technique has been developed for the determination of pyronaridine (PND), an antimalarial drug, in human plasma. After extraction with C18 solid-phase sorbent, PND was analyzed using a reverse phase chromatographic method with fluorescence detection (at lambda(ex)=267 nm and lambda(em)=443 nm). The mean extraction recovery for PND was 95.2%. The coefficient of variation for intra-assay precision, inter-assay precision and accuracy was less than 10%. The quantification limit with fluorescence detection was 0.010 microg/mL plasma. The method described herein has several advantages over other published methods since it is easy to perform and rapid. It also permits reducing both, solvent use and sample preparation time. The method has been used successfully to assay plasma samples from clinical pharmacokinetic studies.

A series of 5-(5,6)-dihydrouracil substituted 8-hydroxy-[1,6]naphthyridine-7-carboxylic acid 4-fluorobenzylamide inhibitors of HIV-1 integrase and viral replication in cells

Introduction of a 5,6-dihydrouracil functionality in the 5-position of N-(4-fluorobenzyl)-8-hydroxy-[1,6]naphthyridine-7-carboxamide 1 led to a series of highly active HIV-1 integrase inhibitors. These compounds displayed low nanomolar activity in inhibiting both the strand transfer process of HIV-1 integrase and viral replication in cells. Compound 11 is a 150-fold more potent antiviral agent than 1, with a CIC(95) of 40 nM in the presence of human serum. It displays good pharmacokinetics when dosed in rats and dogs.

Antimicrobial activity and a comparison of published pharmacodynamics of gemifloxacin and eight fluoroquinolones against Streptococcus pneumoniae

Gemifloxacin was evaluated for its in vitro activity and was compared with eight fluoroquinolones. Pharmacodynamic comparisons were made based on published pharmacokinetic information. Gemifloxacin demonstrated excellent in vitro activity (minimum inhibitory concentration necessary to inhibit 90% of the strains tested, MIC90 = 0.03 mg/L (range 0.0019-0.03 mg/L)) against 199 strains of Streptococcus pneumoniae. Its activity was not influenced by penicillin or ciprofloxacin non-susceptibility. Gemifloxacin demonstrated excellent pharmacodynamic parameters, with a Cmax/MIC90 of 67 (where Cmax is the peak serum level) and an AUC/MIC90 of 297 (where AUC is the area under the curve). Compared with the other eight fluoroquinolones tested, gemifloxacin demonstrated the best in vitro activity and Cmax/MIC90.

Gemifloxacin for the treatment of respiratory tract infections: in vitro susceptibility, pharmacokinetics and pharmacodynamics, clinical efficacy, and safety

Gemifloxacin is a synthetic fluoroquinolone antimicrobial agent exhibiting potent activity against most gram-negative and gram-positive organisms, such as the important community-acquired respiratory pathogens Streptococcus pneumoniae (including multidrug-resistant S. pneumoniae), Haemophilus influenzae , and Moraxella catarrhalis . The agent's mechanism of action involves dual targeting of two essential bacterial enzymes: DNA gyrase and topoisomerase IV. Gemifloxacin was approved by the Food and Drug Administration in April 2003 for treatment of community-acquired pneumonia and acute bacterial exacerbation of chronic bronchitis. The drug has an oral bioavailability of approximately 71%. Approximately 20-35% of gemifloxacin is excreted unchanged in the urine after 24 hours. The elimination half-life of gemifloxacin is 6-8 hours in patients with normal renal function, supporting once-daily dosing. The 24-hour free-drug area under the plasma concentration-time curve:minimum inhibitory concentration ratio (fAUC(0-24):MIC) associated with efficacy, based on results from in vitro and animal models of infection, is approximately 30. With a mean fAUC(0-24) of approximately 3 microg*hour/ml (35% of total AUC(0-24) of 8.4) and a median S. pneumoniae MIC for 90% of tested strains of 0.03, a fAUC(0-24):MIC ratio of 100 would be expected after standard dosing (320 mg once/day). In clinical studies involving both hospitalized and outpatient populations, gemifloxacin has been highly effective in the treatment of community-acquired pneumonia and acute exacerbation of chronic bronchitis. Clinical success rates ranged from 93.9-95.9% in patients with community-acquired pneumonia and 96.1-97.5% in those with acute exacerbation of chronic bronchitis. Gemifloxacin is well tolerated; the frequency of adverse events with this agent is low. Most adverse events are mild-to-moderate in severity, with diarrhea (< 4%), nausea and rash (< 3%), and headache (< 2%) most commonly reported. Drug interactions with gemifloxacin are not common, although absorption is greatly reduced when given with divalent and trivalent cation-containing compounds, such as antacids. Due to its potent activity against many common gram-positive and gram-negative respiratory pathogens, its proven clinical efficacy, and its favorable safety profile, gemifloxacin is a highly effective empiric treatment for community-acquired lower respiratory tract infections.

Activity of gemifloxacin against quinolone-resistant Streptococcus pneumoniae strains in vitro and in a mouse pneumonia model

Gemifloxacin is a novel fluoronaphthyridone quinolone with enhanced in vitro activity against Streptococcus pneumoniae. We investigated the activities of gemifloxacin and trovafloxacin, their abilities to select for resistance in vitro and in vivo, and their efficacies in a mouse model of acute pneumonia. Immunocompetent Swiss mice were infected with 10(5) CFU of a virulent, encapsulated S. pneumoniae strain, P-4241, or its isogenic parC, gyrA, parC gyrA, and efflux mutant derivatives (serotype 3); and leukopenic mice were infected with 10(7) CFU of two poorly virulent clinical strains (serotype 11A) carrying either a parE mutation or a parC, gyrA, and parE triple mutation. The drugs were administered six times every 12 h, starting at either 3 or 18 h postinfection. In vitro, gemifloxacin was the most potent agent against strains with and without acquired resistance to fluoroquinolones. While control mice died within 6 days, gemifloxacin at doses of 25 and 50 mg/kg of body weight was highly effective (survival rates, 90 to 100%) against the wild-type strain and against mutants harboring a single mutation, corresponding to area under the time-versus-serum concentration curve at 24 h (AUC(24))/MIC ratios of 56.5 to 113, and provided a 40% survival rate against a mutant with a double mutation (parC and gyrA). A total AUC(24)/MIC ratio of 28.5 was associated with poor efficacy and the emergence of resistant mutants. Trovafloxacin was as effective as gemifloxacin against mutants with single mutations but did not provide any protection against the mutant with double mutations, despite treatment with a high dose of 200 mg/kg. Gemifloxacin preferentially selected for parC mutants both in vitro and in vivo.

Assessment of pharmacokinetic-pharmacodynamic target attainment of gemifloxacin against Streptococcus pneumoniae

The treatment of community-acquired respiratory tract infections has been complicated by the emergence of multidrug-resistant Streptococcus pneumoniae. Although traditionally rare, a growing concern for fluoroquinolone-resistant pneumococci has surfaced. More pharmacodynamically potent antimicrobial agents are clearly needed, as the use of such agents may further optimize clinical and microbiological outcomes for patients and slow the emergence of fluoroquinolone resistance. For fluoroquinolones, the ratio of the 24-h area under the concentration-time curve of the agent to the minimum inhibitory concentration of the agent against the pathogen for the fraction of unbound drug is the major pharmacokinetic-pharmacodynamic (PK-PD) measure correlating with efficacy in nonclinical models and infected patients. A 2500-patient Monte Carlo simulation, utilizing a patient-population pharmacokinetic model derived from phase 3 registration trials and the minimum inhibitory concentration distribution for gemifloxacin against 3117 clinical strains of S. pneumoniae, was carried out to estimate the probability of gemifloxacin attaining exposures associated with efficacy. The overall probability PK-PD target attainment for gemifloxacin was greater than 0.99. Gemifloxacin is among the most pharmacodynamically potent fluoroquinolones and is more potent than ciprofloxacin, ofloxacin, and levofloxacin. Preferential use of pharmacodynamically potent agents over other alternatives may lead to improved clinical outcomes and decreased selection of fluoroquinolone-resistant pneumococci.

Concentrations of gemifloxacin at the target site in healthy volunteers after a single oral dose

Free gemifloxacin concentrations in the interstitial space fluid of skeletal muscle and subcutaneous adipose tissue were measured by means of in vivo microdialysis to characterize the ability of gemifloxacin to penetrate human soft tissues. Twelve healthy volunteers received a single oral dose of 320 mg of gemifloxacin. The mean areas under the concentration-time curves from 0 to 10 h (AUC(0-10)) were significantly higher for soft tissue than for unbound gemifloxacin in plasma (P < 0.05). The ratios of the mean AUC(0-10) for tissue to the AUC(0-10) for free gemifloxacin in plasma were 1.7 +/- 0.7 (mean +/- standard deviation) for skeletal muscle and 2.4 +/- 1.0 for adipose tissue. The AUC(0-24) ratios for free gemifloxacin in tissues to the MIC at which 90% of frequently isolated bacteria are inhibited were close to or higher than 100 h. Therefore, based on pharmacokinetic and pharmacodynamic calculations, we conclude that gemifloxacin might be a useful therapeutic option for the treatment of soft tissue infections.

Nonpeptide alphavbeta3 antagonists. Part 11: discovery and preclinical evaluation of potent alphavbeta3 antagonists for the prevention and treatment of osteoporosis

3-(S)-Pyrimidin-5-yl-9-(5,6,7,8-tetrahydro-[1,8]naphthyridin-2-yl)-nonanoic acid (5e) and 3-(S)-(methylpyrimidin-5-yl)-9-(5,6,7,8-tetrahydro-[1,8]naphthyridin-2-yl)-nonanoic acid (5f) were identified as potent and selective antagonists of the alpha(v)beta(3) receptor. These compounds have excellent in vitro profiles (IC(50) = 0.07 and 0.08 nM, respectively), significant unbound fractions in human plasma (6 and 4%), and good pharmacokinetics in rat, dog, and rhesus monkey. On the basis of the efficacy shown in an in vivo model of bone turnover following once-daily oral administration, these two compounds were selected for clinical development for the treatment of osteoporosis.

Liquid chromatographic determination of pyronaridine in human plasma and oral dosage form

A new procedure for the determination of pyronaridine in plasma by reversed-phase high performance liquid chromatography (HPLC) with UV detection at 278 nm is described. The method involves liquid-liquid extraction of the drug with diethyl ether following basification of the deproteinized plasma with alkaline phosphate buffer. Chromatographic separation was achieved using a microbore C-18 column and a mobile phase consisting of 0.1% aqueous trifluoroacetic acid (TFA)-acetonitrile (75:25% (v/v)), pH 2.2, at a flow rate of 0.07 ml/min. Papaverine was used as internal standard. The response was linear between 50 and 1500 ng/ml. The limit of quantitation (LOQ) after plasma extraction was 50 ng/ml, the intra- and inter-day precision ranged from 2.5 to 13.8% (CV). The recovery of the drug from plasma and accuracy were >90%. Preliminary application of the method for monitoring pyronaridine in humans upon oral administration of the tablet demonstrated the principal usefulness of the assay for clinical trial studies. The method can also be used to analyze the compound in pharmaceutical formulations.

Gemifloxacin: a new fluoroquinolone approved for treatment of respiratory infections

OBJECTIVE

To evaluate the microbiology, pharmacokinetic parameters, drug interactions, and results of the available clinical trials of gemifloxacin for the treatment of community-acquired pneumonia (CAP) and acute exacerbation of chronic bronchitis (AECB).

DATA SOURCES

MEDLINE (1966-September 2003) was searched for primary and review articles. Data from the manufacturer were also included. Key words included adverse effects, clinical trials, drug interactions, gemifloxacin, and pharmacokinetic parameters.

STUDY SELECTION AND DATA EXTRACTION

All articles and product labeling concerning gemifloxacin, a fluoroquinolone antibiotic recently approved by the Food and Drug Administration for treatment of CAP and AECB, were included for review.

DATA SYNTHESIS

Compared with currently available fluoroquinolones, gemifloxacin demonstrated improved in vitro activity against Streptococcus pneumoniae (minimum inhibitory concentration for 90% eradication 0.03 microg/mL) and similar activity against gram-negative respiratory pathogens (Haemophilus influenzae, Moraxella catarrhalis) and atypical pathogens such as Chlamydia pneumoniae, Legionella pneumophila, and Mycoplasma pneumoniae. Gemifloxacin, consistent with other available fluoroquinolones, has insufficient activity against methicillin-resistant Staphylococcus aureus to allow clinical use for such infections. Gemifloxacin has adequate bioavailability and a favorable drug interaction profile. Gemifloxacin was comparable to commonly employed nonfluoroquinolone regimens for treatment of CAP and AECB, although the studies were designed to demonstrate equivalence. Gemifloxacin once daily for 5-7 days was well tolerated in controlled and uncontrolled clinical studies. Available clinical data, however, are insufficient to draw clinical or toxicologic distinctions between gemifloxacin and other fluoroquinolones.

CONCLUSIONS

Gemifloxacin may be a suitable choice for empiric treatment of CAP or AECB. However, due to the significant history of fluoroquinolone-induced hepatic failure and dermatologic complications, the use of this drug should be closely monitored.

Serum bactericidal activity of gemifloxacin versus clarithromycin against Streptococcus pneumoniae with different susceptibility to quinolones

The objective of this study was to determine serum bactericidal titers (SBT, the highest dilution of serum showing no growth) and the serum bactericidal activity (SBA, i.e. duration of SBT greater than 1:2) as well as the serum bactericidal rate of gemifloxacin and clarithromycin after single doses in healthy male volunteers against Streptococcus pneumoniae. Strains tested had various degrees of susceptibility to penicillin as well as different susceptibility to quinolones due to a different QRDR mutation pattern (parC, gyrA). Serum samples from volunteers (n = 12) who had received a single oral dose of either 320 mg gemifloxacin or 500 mg clarithromycin in an open-label crossover study were obtained over a 24-hour period. SBA was determined, using the microdilution method. SBA of wildtype strains for gemifloxacin ranged from 8.9 to 15.4 h (mean 12.6 h). For gemifloxacin, 2 strains with solitary gyrA mutation had an SBA from 4.5 to 4.7 h (median 4.5 h). One of the 2 strains with a single QRDR mutation in parC displayed an SBA of 4.5 h, comparable to the gyrA mutation strains, whereas the second strain had a nearly twice as long SBA of 8.9 h. Two strains with two mutations (parC and gyrA) did not display any SBA. For clarithromycin, the duration of SBA ranged from 11.3 to 15.5 h (mean 13.6 h) for 6 of the 12 strains with an MIC < or = 0.06 mg/L (no SBA was found for the remaining strains, with an MIC of 0.25 mg/L or higher). In conclusion, a correlation between individual serum concentrations and SBA was found for both antibiotics.

POLYMORPHIC EXPRESSION OF CYP1A2 LEADING TO INTERINDIVIDUAL VARIABILITY IN METABOLISM OF A NOVEL BENZODIAZEPINE RECEPTOR PARTIAL INVERSE AGONIST IN DOGS

5-(3-methoxyphenyl)-3-(5-methyl-1,2,4-oxadiazol-3-yl)-2-oxo-1,2-dihydro-1,6-naphthyridine (AC-3933) is a novel cognitive enhancer with central benzodiazepine receptor partial inverse agonistic activity. AC-3933 is predominantly metabolized to hydroxylated metabolite [SX-5745; 3-(5-hydroxymethyl-1,2,4-oxadiazol-3-yl)-5-(3-methoxyphenyl)-2-oxo-1,2-dihydro-1,6-naphthyridine] in dog. Initially, we found that there is considerable interindividual variability in AC-3933 hydroxylation in dogs and that dogs could be phenotyped as extensive metabolizer (EM) and poor metabolizer (PM). Then, to clarify the cause of AC-3933 polymorphic hydroxylation in dogs, in vitro studies were carried out using liver microsomes from EM and PM dogs. Our results show that AC-3933 hydroxylation clearance in PM dogs was much lower than that in EM dogs (0.2 versus 10.8-20.5 microl/min/mg, respectively). In addition, AC-3933 hydroxylation was significantly inhibited by alpha-naphthoflavone, a CYP1A inhibitor, and by anti-CYP1A2 antibodies, indicating that CYP1A2 was responsible for the polymorphic hydroxylation of AC-3933 in dogs. Furthermore, immunoblotting results have shown that although CYP1A2 protein was not detected in PM dogs (<0.86 pmol/mg), CYP1A2 content in EM dogs was prominent (6.1-13.0 pmol/mg). These results indicate that AC-3933 polymorphic hydroxylation arises from the polymorphic expression of CYP1A2 in dogs, which might involve genetic polymorphism of the CYP1A2 gene.

Simulated in vitro quinolone pharmacodynamics at clinically achievable AUC/MIC ratios: advantage of I E over other integral parameters

To compare the antimicrobial effects of clinically achievable ratios of area under the curve (AUC) to MIC, a clinical isolate of Moraxella catarrhalis was selected with MICs corresponding to the MIC(50)s of four quinolones. Monoexponentially declining concentrations observed in human plasma after oral administration of 1,000 mg of ciprofloxacin (as two 500-mg doses at a 12-hour interval), 320 mg gemifloxacin, 500 mg levofloxacin or 400 mg moxifloxacin (each as a single dose) and were simulated in an in vitro dynamic model. The respective half-lives were 4, 7.4, 6.8 and 12.1 h, and the AUC/MICs were 730, 1,130, 920 and 690 h. The time-kill/regrowth curves yielded similar patterns with the four quinolones: a rapid reduction in bacterial numbers followed by bacterial regrowth that occurred later with moxifloxacin than with ciprofloxacin, gemifloxacin, and levofloxacin. The total antimicrobial effect of moxifloxacin as expressed by the I(E) parameter (area between the control growth and time- kill curves from time zero to the time when bacterial counts on the regrowth curve achieve the same maximal numbers as in the absence of antimicrobial) was 30, 55, and 120% greater than gemifloxacin, levofloxacin and ciprofloxacin, respectively. Unlike I(E), the other integral indices determined over a fixed time (24 h) - the area between the control growth and time-kill curves, area above the time-kill curve and area under the time-kill curve were similar for the four fluoroquinolones, thus precluding their differentiation.

Treatment of Experimental Bacterial Keratitis With Topical Trovafloxacin

OBJECTIVE

To investigate the therapeutic role of trovafloxacin mesylate, a newer-generation fluoroquinolone with an expanded spectrum of activity, in the treatment of experimental bacterial keratitis.

METHODS

Susceptibility studies were performed on various strains of ocular isolates to determine the minimum inhibitory concentration (MIC) of trovafloxacin compared with ciprofloxacin and ofloxacin, using the E-test method. Pharmacokinetic studies were performed by a single topical administration of trovafloxacin to rabbit eyes with either an intact or denuded corneal epithelium. Aqueous humor, vitreous, and corneal concentrations of trovafloxacin were determined at different time points. Experimental bacterial keratitis studies were performed in rabbit eyes. Three identical studies were conducted using Staphylococcus aureus, Streptococcus pneumoniae, or Pseudomonas aeruginosa. Therapy groups included 0.5% trovafloxacin, 0.3% ciprofloxacin, 0.3% ofloxacin, and isotonic sodium chloride solution. After 12 hours of drops administration, corneas were excised, homogenized, and serially plated. The main outcome measure was quantitative bacteriologic analysis for residual colony-forming units.

RESULTS

In vitro susceptibility study findings indicated that the MIC of trovafloxacin was significantly lower than the MIC of ciprofloxacin and ofloxacin for S. aureus, S. pneumoniae, and Haemophilus influenzae, lower than the MIC of ciprofloxacin and ofloxacin for Staphylococcus epidermidis, and intermediate between ciprofloxacin and ofloxacin for P. aeruginosa. Pharmacokinetic studies showed a significant concentration of trovafloxacin in the treated corneas, especially in eyes with a denuded epithelium. All serum samples had undetectable trovafloxacin concentrations. Experimental keratitis studies showed a statistically significant decrease of colony-forming units in trovafloxacin-treated eyes in the S. aureus model and a similar decrease in the S pneumoniae and P aeruginosa models.

CONCLUSIONS

Topical 0.5% trovafloxacin proved to be an effective ocular medication for the therapy of gram-positive and gram-negative keratitis. Clinical Relevance Trovafloxacin may provide an excellent therapeutic alternative in bacterial keratitis.

Disposition of a novel and potent alpha(v)beta3 antagonist in animals, and extrapolation to man

1. The disposition of 3-[2-oxo-3-[3-(5,6,7,8-tetrahydro-[1,8]naphthyridin-2-yl) propyl]-imidazolidin-1-yl]-3(S)-(6-methoxy-pyridin-3-yl)propionic acid (compound A), a potent and selective alpha(v)beta(3) antagonist, was characterized in several animal species in support of its selection for preclinical safety studies and potential clinical development. 2. Compound A exhibited marked species differences in pharmacokinetics; the plasma clearances and bioavailabilities ranged from 33-47 ml min(-1) kg(-1) in rats and mice to 4-9 ml min(-1) kg(-1) in dogs and monkeys, and about 20% in rats to 70-80% in dogs and monkeys, respectively. Both the intravenous (i.v.) and oral kinetics of compound A were linear over the dose range studied in dogs (0.1-5 mg kg(-1) i.v. and 0.25-20 mg kg(-1) orally [p.o.]) and rats (1-30 mg kg(-1) i.v. and 4-160 mg kg(-1) p.o.). 3. Compound A was eliminated substantially by urinary excretion; the urinary recovery of the unchanged drug was 67% in rhesus, 48% in dogs and about 30% in rats. In these animal species, biotransformation was modest. 4. Following i.v. administration of [(14)C]-compound A to rats, the radioactivity rapidly distributed to all tissues investigated, with high levels of the radioactivity detected in liver, kidney and intestine soon after the drug administration. The radioactivity declined rapidly, with less than 1% of the i.v. dose remaining at 30-h post-dose. 5. Compound A was moderately bound to plasma proteins, with unbound fractions of 26, 20, 14 and 5% for rats, dogs, monkeys and humans, respectively. It was bound primarily to human alpha(1)-acid glycoprotein (about 85% binding at 0.1% concentration), as compared with human albumin (< 50% binding at 4% concentration). 6. Using simple allometry, compound A was predicted to exhibit relatively low clearance (1-3 ml min(-1) kg(-1)) and low volume of distribution (0.1-0.3 l kg(-1)) in humans. Based on the predicted values, compound A was projected to exhibit a favourable oral pharmacokinetic profile in humans, with good bioavailability (50-80%). These predicted values provided a basis for compound selection for further development.

In vitro pharmacodynamic activity of gatifloxacin, gemifloxacin, moxifloxacin and levofloxacin against Streptococcus pneumoniae containing specific mutations in DNA gyrase and topoisomerase IV

An in vitro pharmacodynatnic modeling apparatus (PDMA) generated specific bacterial kill profiles for single-dose regimens of gatifloxacin (GT), gemifloxacin (GM), moxifloxacin (MX) and levofloxacin (LV) against isolates of Streptococcus pneumoniae with specific QRDR profiles: SP-WT (no modifications); SP-C (changes in parC); and SP-AC (changes in both parC and gyrA). No differences in 3-log reduction time or total log reduction were observed among the four agents for SP-WT; however, LV failed to achieve a 3-log reduction in SP-C and SP-AC, and total log reduction after 12 hrs was minimal compared to the other agents. GM and MX required less time for 3-log reduction of SP-AC compared to GT, but total log reductions in SP-AC were similar among the three newer quinolone agents (GM > MX > GT). The study isolates with QRDR modifications greatly reduced LV activity. GM and MX maintained the greatest degree of activity against all study isolates and their activity was not adversely influenced by the genetic modifications in SP-C and SP-AC. The dual targeting characteristic of GM was also assessed, but did not offer significant advantages relative to MX and GT.

Gatifloxacin, Gemifloxacin, and Moxifloxacin: The Role of 3 Newer Fluoroquinolones

Gatifloxacin, gemifloxacin, and moxifloxacin are the newest fluoroquinolones and show excellent in vitro activity against a wide variety of respiratory tract pathogens, many gram-negative aerobic organisms, and Bacteroides fragilis. These agents may be administered as oral and/or intravenous formulations with excellent bioavailability. The pharmacodynamics of these 3 new fluoroquinolones is more favorable than that of levofloxacin or ciprofloxacin for Streptococcus pneumoniae. All 3 agents are approved for the treatment of acute exacerbation of chronic bronchitis and community-acquired pneumonia. In addition, gatifloxacin and moxifloxacin are approved for the treatment of sinusitis. The toxicity of these 3 agents appears to be similar to that of the other fluoroquinolones in terms of gastrointestinal and central nervous system disturbances. All 3 agents have a low risk of phototoxicity, but gemifloxacin is associated with an increased risk of skin rash that is not a photoreaction. These agents can be useful for treatment of bacterial respiratory tract infections in patients who are allergic to beta-lactams, but caution must be exercised to avoid the potential for selection of widespread resistance, which may occur with indiscriminate use.

Effect of calcium carbonate on bioavailability of orally administered gemifloxacin

We investigated the effect of calcium carbonate on the oral bioavailability of gemifloxacin. Gemifloxacin was administered alone, 2 h before, simultaneously, or 2 h after calcium carbonate in 16 volunteers. Data for 320 mg of gemifloxacin alone were as follows: maximum concentration of drug in serum (C(max)),13 microg/ml; half-life, 7.33 h; and area under the concentration-time curve from 0 h to infinity (AUC( infinity )), 6.79 microg. h/ml. Only simultaneous coadministration of calcium carbonate reduced C(max) (-17%) and AUC( infinity ) (-21%) significantly.

Serum bactericidal activity of trovafloxacin, in combination with cefepime or amikacin, in healthy volunteers

OBJECTIVE

To investigate the phamacokinetics and serum bactericidal activities (SBAs) of trovafloxacin, cefepime and amikacin alone and trovafloxacin in combination with cefepime or amikacin, so that the most favorable combination with trovafloxacin can be determined.

METHODS

In this open, randomized, crossover study, 12 healthy volunteers (six females, six males; mean age +/- SD, 25.1 +/- 2.6 years) received an infusion of either 300 mg of alatrovafloxacin or 2000 mg of cefepime or 6 mg/kg body weight amikacin alone, or 300 mg of alatrovafloxacin plus 2000 mg of cefepime or plus 6 mg/kg body weight amikacin. The SBAs against Pseudomonas aeruginosa, Staphylococcus aureus (11 strains each), Citrobacter freundii and Acinetobacter spp. (10 strains each) 1, 10 and 24 h after drug administration were measured by a standard microdilution method. Concentrations of trovafloxacin, cefepime and amikacin in serum and urine were analyzed before and up to 10 and 12 h, respectively, after drug infusion.

RESULTS

Significant synergistic effects on SBA were observed with the combination of trovafloxacin and cefepime against P. aeruginosa, S. aureus and Acinetobacter spp. 1 h after drug administration, and against Citrobacter freundii 1, 10 and 24 h after drug administration. The combination of trovafloxacin and amikacin showed significant synergistic effects against P. aeruginosa, S. aureus and C. freundii 1 h after drug administration. The combination of trovafloxacin and cefepime was, in general, more active than the combination of trovafloxacin and amikacin. No significant differences in the serum concentrations of trovafloxacin were observed between single and combined administration. However, the maximal concentration of cefepime was significantly lower when it was used in combination with trovafloxacin.

CONCLUSION

Our study suggests a favorable interaction between trovafloxacin and cefepime. This combination showed more synergistic bactericidal activity against most of the test strains compared to the combination of trovafloxacin and amikacin. However, for P. aeruginosa, the bactericidal activity of cepefime alone was higher than that of the combination with trovafloxacin.

Efficacy and pharmacodynamics of gemifloxacin versus levofloxacin in guinea pig pneumococcal pneumonia induced by strains with decreased ciprofloxacin susceptibility

Quinolone in vivo bactericidal activity was investigated in a guinea pig pneumonia model using three Streptococcus pneumoniae strains with decreasing susceptibility to ciprofloxacin. Treatment regimens resulted in values of AUC(0-24 h) and C(30 min) similar to those of standard oral regimens in human serum. Efficacy was defined as a significant difference in number of viable bacteria in the lungs compared with the control. Ciprofloxacin, levofloxacin and gemifloxacin were effective against the levofloxacin-susceptible strain. Only gemifloxacin achieved a >/=99.9% reduction versus control against the levofloxacin intermediate-resistant strain. Gemifloxacin achieved a 99.69% reduction and was the only quinolone significantly different from the control (P<0.05) against the levofloxacin-resistant strain. Gemifloxacin offers in vivo activity against ciprofloxacin- to levofloxacin-resistant pneumococci.

The design of 8,8-dimethyl[1,6]naphthyridines as potential anticonvulsant agents

Starting from a series of 7-linked tetrahydroisoquinoline derivatives, as exemplified by SB-270664, a new series of 8,8-dimethylnaphthyridine compounds has been identified. SAR studies around these attractive leads have provided compounds such as 12 which display excellent anticonvulsant activity and an encouraging pharmacokinetic profile in vivo.