The Pharmacokinetic Effect of Itraconazole and Voriconazole on Ripretinib in Beagle Dogs by UPLC-MS/MS Technique

BACKGROUND

A new UPLC-MS/MS technique for the determination of ripretinib in beagle dog plasma was developed, and the pharmacokinetic effects of voriconazole and itraconazole on ripretinib in beagle dogs were studied.

METHODS

After extraction with ethyl acetate under alkaline conditions, ripretinib was detected using avapritinib as the internal standard (IS). The mobile phases were 0.1% formic acid-acetonitrile. The scanning method was multi-reaction monitoring using ESI+ source, and the ion pairs for ripretinib and IS were m/z 509.93→416.85 and 499.1→482.09, respectively. This animal experiment adopted a three period self-control experimental design. In the first period, ripretinib was orally administered to six beagle dogs at a dose of 5 mg/kg. In the second period, the same six beagle dogs were orally given itraconazole at a dose of 7 mg/kg, after 30 min, ripretinib was orally given. In the third period, voriconazole at a dose of 7 mg/kg was given orally, and then ripretinib was orally given. At different time points, the blood samples were collected. The concentration of ripretinib was detected, and the pharmacokinetic parameters of ripretinib were calculated.

RESULTS

Ripretinib had a good linear relationship in the range of 1-1000 ng/mL. The precision, accuracy, recovery, matrix effect and stability met the requirements of the guiding principles. After erdafitinib combined with itraconazole, the Cmax and AUC0→t of ripretinib increased by 38.35% and 36.36%, respectively, and the t1/2 was prolonged to 7.53 h. After ripretinib combined with voriconazole, the Cmax and AUC0→t of ripretinib increased by 37.44% and 25.52%, respectively, and the t1/2 was prolonged to 7.33 h.

CONCLUSION

A new and reliable UPLC-MS/MS technique was fully optimized and developed to detect the concentration of ripretinib in beagle dog plasma. Itraconazole and voriconazole could inhibit the metabolism of ripretinib in beagle dogs and increase the plasma exposure of ripretinib.

DNA-Binding Anticancer Drugs: One Target, Two Actions

Amsacrine, an anticancer drug first synthesised in 1970 by Professor Cain and colleagues, showed excellent preclinical activity and underwent clinical trial in 1978 under the auspices of the US National Cancer Institute, showing activity against acute lymphoblastic leukaemia. In 1984, the enzyme DNA topoisomerase II was identified as a molecular target for amsacrine, acting to poison this enzyme and to induce DNA double-strand breaks. One of the main challenges in the 1980s was to determine whether amsacrine analogues could be developed with activity against solid tumours. A multidisciplinary team was assembled in Auckland, and Professor Denny played a leading role in this approach. Among a large number of drugs developed in the programme, N-[2-(dimethylamino)-ethyl]-acridine-4-carboxamide (DACA), first synthesised by Professor Denny, showed excellent activity against a mouse lung adenocarcinoma. It underwent clinical trial, but dose escalation was prevented by ion channel toxicity. Subsequent work led to the DACA derivative SN 28049, which had increased potency and reduced ion channel toxicity. Mode of action studies suggested that both amsacrine and DACA target the enzyme DNA topoisomerase II but with a different balance of cellular consequences. As primarily a topoisomerase II poison, amsacrine acts to turn the enzyme into a DNA-damaging agent. As primarily topoisomerase II catalytic inhibitors, DACA and SN 28049 act to inhibit the segregation of daughter chromatids during anaphase. The balance between these two actions, one cell cycle phase specific and the other nonspecific, together with pharmacokinetic, cytokinetic and immunogenic considerations, provides links between the actions of acridine derivatives and anthracyclines such as doxorubicin. They also provide insights into the action of cytotoxic DNA-binding drugs.

Penetration, distribution, and elimination of remofuscin/soraprazan in Stargardt mouse eyes following a single intravitreal injection using pharmacokinetics and transmission electron microscopic autoradiography: Implication for the local treatment of Stargardt's disease and dry age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in older people in the developed world while Stargardt's disease (SD) is a juvenile macular degeneration and an orphan disease. Both diseases are untreatable and are marked by accumulation of lipofuscin advancing to progressive deterioration of the retinal pigment epithelium (RPE) and retina and subsequent vision loss till blindness. We discovered that a small molecule belonging to the tetrahydropyridoether class of compounds, soraprazan renamed remofuscin, is able to remove existing lipofuscin from the RPE. This study investigated the drug penetration, distribution, and elimination into the eyes of a mouse model for increased lipofuscinogenesis, following a single intravitreal injection. We measured the time course of concentrations of remofuscin in different eye tissues using high-performance liquid chromatography combined with mass spectroscopy (HPLC-MS). We also visualized the penetration and distribution of 3 H-remofuscin in eye sections up to 20 weeks post-injection using transmission electron microscopic (TEM) autoradiography. The distribution of silver grains revealed that remofuscin accumulated specifically in the RPE by binding to the RPE pigments (melanin, lipofuscin and melanolipofuscin) and that it was still detected after 20 weeks. Importantly, the melanosomes in choroidal melanocytes only rarely bind remofuscin emphasizing its potential to serve as an active ingredient in the RPE for the treatment of SD and dry AMD. In addition, our study highlights the importance of electron microscopic autoradiography as it is the only method able to show drug binding with a high intracellular resolution.

Switch Control Inhibition of KIT and PDGFRA in Patients With Advanced Gastrointestinal Stromal Tumor: A Phase I Study of Ripretinib

PURPOSE

In advanced gastrointestinal stromal tumor (GIST), there is an unmet need for therapies that target both primary and secondary mutations of pathogenic KIT/PDGFRA oncoproteins. Ripretinib is a novel switch-control kinase inhibitor designed to inhibit a wide range of KIT and PDGFRA mutations.

PATIENTS AND METHODS

This first-in-human, to our knowledge, phase I study of ripretinib (ClinicalTrials.gov identifier: NCT02571036) included a dose-escalation phase and subsequent expansion phase at the recommended phase II dose (RP2D). Eligible patients included those with advanced GIST, intolerant to or experienced progression on ≥ 1 line of systemic therapy, and other advanced malignancies. Safety, dose-limiting toxicities (DLTs), maximum-tolerated dose (MTD), and preliminary antitumor activity were evaluated.

RESULTS

At data cutoff (August 31, 2019), 258 patients (n = 184 GIST) were enrolled, with 68 patients in the dose-escalation phase. Three DLTs were reported: grade 3 lipase increase (n = 2; 100 mg and 200 mg twice a day) and grade 4 increased creatine phosphokinase (n = 1; 150 mg once daily). MTD was not reached (maximum dose evaluated, 200 mg twice a day); 150 mg once daily was established as the RP2D. The most frequent (> 30%) treatment-emergent adverse events in patients with GIST receiving ripretinib 150 mg once daily (n = 142) were alopecia (n = 88 [62.0%]), fatigue (n = 78 [54.9%]), myalgia (n = 69 [48.6%]), nausea (n = 65 [45.8%]), palmar-plantar erythrodysesthesia (n = 62 [43.7%]), constipation (n = 56 [39.4%]), decreased appetite (n = 48 [33.8%]), and diarrhea (n = 47 [33.1%]). Objective response rate (confirmed) of 11.3% (n = 16/142) ranging from 7.2% (n = 6/83; fourth line or greater) to 19.4% (n = 6/31; second line) and median progression-free survival ranging from 5.5 months (fourth line or greater) to 10.7 months (second line), on the basis of investigator assessment, were observed.

CONCLUSION

Ripretinib is a well-tolerated, novel inhibitor of KIT and PDGFRA mutant kinases with promising activity in patients with refractory advanced GIST.

Synthesis and preliminary studies of 11C-labeled tetrahydro-1,7-naphthyridine-2-carboxamides for PET imaging of metabotropic glutamate receptor 2

Selective modulation of metabotropic glutamate receptor 2 (mGlu2) represents a novel therapeutic approach for treating brain disorders, including schizophrenia, depression, Parkinson's disease (PD), Alzheimer's disease (AD), drug abuse and addiction. Imaging mGlu2 using positron emission tomography (PET) would allow for in vivo quantification under physiological and pathological conditions and facilitate drug discovery by enabling target engagement studies. In this paper, we aimed to develop a novel specific radioligand derived from negative allosteric modulators (NAMs) for PET imaging of mGlu2. Methods. A focused small molecule library of mGlu2 NAMs with tetrahydro naphthyridine scaffold was synthesized for pharmacology and physicochemical evaluation. GIRK dose-response assays and CNS panel binding selectivity assays were performed to study the affinity and selectivity of mGlu2 NAMs, among which compounds 14a and 14b were selected as PET ligand candidates. Autoradiography in SD rat brain sections was used to confirm the in vitro binding specificity and selectivity of [11C]14a and [11C]14b towards mGlu2. In vivo binding specificity was then studied by PET imaging. Whole body biodistribution study and radiometabolite analysis were conducted to demonstrate the pharmacokinetic properties of [11C]14b as most promising PET mGlu2 PET ligand. Results. mGlu2 NAMs 14a-14g were synthesized in 14%-20% yields in five steps. NAMs 14a and 14b were selected to be the most promising ligands due to their high affinity in GIRK dose-response assays. [11C]14a and [11C]14b displayed similar heterogeneous distribution by autoradiography, consistent with mGlu2 expression in the brain. While PET imaging study showed good brain permeability for both tracers, compound [11C]14b demonstrated superior binding specificity compared to [11C]14a. Further radiometabolite analysis of [11C]14b showed excellent stability in the brain. Conclusions. Compound 14b exhibited high affinity and excellent subtype selectivity, which was then evaluated by in vitro autoradiography and in vivo PET imaging study after labeling with carbon-11. Ligand [11C]14b, which we named [11C]MG2-1904, demonstrated high brain uptake and excellent in vitro/in vivo specific binding towards mGlu2 with high metabolic stability in the brain. As proof-of-concept, our preliminary work demonstrated a successful example of visualizing mGlu2in vivo derived from NAMs, which represents a promising chemotype for further development and optimization aimed for clinical translation.

Pyronaridine tetraphosphate efficacy against Ebola virus infection in guinea pig

The recent outbreaks of the Ebola virus (EBOV) in Africa have brought global visibility to the shortage of available therapeutic options to treat patients infected with this or closely related viruses. We have recently computationally identified three molecules which have all demonstrated statistically significant efficacy in the mouse model of infection with mouse adapted Ebola virus (ma-EBOV). One of these molecules is the antimalarial pyronaridine tetraphosphate (IC50 range of 0.82-1.30 μM against three strains of EBOV and IC50 range of 1.01-2.72 μM against two strains of Marburg virus (MARV)) which is an approved drug in the European Union and used in combination with artesunate. To date, no small molecule drugs have shown statistically significant efficacy in the guinea pig model of EBOV infection. Pharmacokinetics and range-finding studies in guinea pigs directed us to a single 300 mg/kg or 600 mg/kg oral dose of pyronaridine 1hr after infection. Pyronaridine resulted in statistically significant survival of 40% at 300 mg/kg and protected from a lethal challenge with EBOV. In comparison, oral favipiravir (300 mg/kg dosed once a day) had 43.5% survival. All animals in the vehicle treatment group succumbed to disease by study day 12 (100% mortality). The in vitro metabolism and metabolite identification of pyronaridine and another of our EBOV active molecules, tilorone, suggested significant species differences which may account for the efficacy or lack thereof, respectively in guinea pig. In summary, our studies with pyronaridine demonstrates its utility for repurposing as an antiviral against EBOV and MARV.

Repurposing the antimalarial pyronaridine tetraphosphate to protect against Ebola virus infection

Recent outbreaks of the Ebola virus (EBOV) have focused attention on the dire need for antivirals to treat these patients. We identified pyronaridine tetraphosphate as a potential candidate as it is an approved drug in the European Union which is currently used in combination with artesunate as a treatment for malaria (EC₅₀ between 420 nM—1.14 μM against EBOV in HeLa cells). Range-finding studies in mice directed us to a single 75 mg/kg i.p. dose 1 hr after infection which resulted in 100% survival and statistically significantly reduced viremia at study day 3 from a lethal challenge with mouse-adapted EBOV (maEBOV). Further, an EBOV window study suggested we could dose pyronaridine 2 or 24 hrs post-exposure to result in similar efficacy. Analysis of cytokine and chemokine panels suggests that pyronaridine may act as an immunomodulator during an EBOV infection. Our studies with pyronaridine clearly demonstrate potential utility for its repurposing as an antiviral against EBOV and merits further study in larger animal models with the added benefit of already being used as a treatment against malaria.

To date there is no approved drug for Ebola Virus infection. Our approach has been to assess drugs that are already approved for other uses in various countries. Using computational models, we have previously identified three such drugs and demonstrated their activity against the Ebola virus in vitro. We now report on the in vitro absorption, metabolism, distribution, excretion and pharmacokinetic properties of one of these molecules, namely the antimalarial pyronaridine. We justify efficacy testing in the mouse model of ebola infection. We also demonstrate that a single dose of this drug is 100% effective against the virus. This study provides important preclinical evaluation of this already approved drug and justifies its selection for larger animal efficacy studies.

Optimization and in line potentiometric monitoring of enhanced photocatalytic degradation kinetics of gemifloxacin using TiO2 nanoparticles/H2O2

Gemifloxacin (GEM) is a broad-spectrum quinolone antibiotic. The presence of GEM residuals in industrial and hospital wastewater has been associated with genotoxicity and antibiotic resistance. In this contribution, the photodegradation of GEM using titanium dioxide nanoparticles (TiO₂NPs)/H₂O₂ as a catalyst was optimized to eliminate residual drug and its photodegradates with antibacterial activity. A half-factorial design was implemented, investigating the effects of pH, initial concentration, H₂O₂ concentration, TiO₂NP loading, and irradiation time. Owing to the time-dependent, multi-transformation of GEM into a wide range of structurally related photodegradation products, the monitoring of GEM throughout the experiments was achieved using both HPLC and potentiometric ion-selective electrodes (ISE). The sensor enabled in-line tracking of residual GEM in the presence of its photodegradates in real time. Results indicated that the pH, irradiation time, and GEM initial concentration were the most significant factors. At the optimum set of experimental conditions, the reaction followed first-order reaction kinetics with a mean percentage degradation of ~ 95% in less than 30 min of irradiation time and almost complete loss of antibacterial activity against Escherichia coli. The promising results demonstrated the efficiency of UV/TiO₂NP/H₂O₂ as a photocatalyst for the breakdown of the pharmacophore of fluoroquinolones from water samples. The high selectivity, minimal solvent consumption, and lack of harmful waste generation confirmed the superiority of in-line monitoring using ISE. Optimization and in-line monitoring protocol should be applicable also at the pharmaceutical industry scale to eliminate the risk of antibiotic resistance.

Identification of lead compounds for (99m)Tc and (18)F GPR91 radiotracers

To develop the first radiotracer targeting GPR91, a cell membrane-bound receptor that modulates the cellular response to hyperglycemia and hypoxia, we designed and prepared a small series of compounds based on a published series of 1,8-naphthyridines with high affinity to GPR91. Our approach provides a mechanism to incorporate radioactive atoms ((99m)Tc and (18)F) into the GPR91 pharmacophore as the final synthetic step. Pharmacological assays confirmed lead compounds for (99m)Tc and (18)F GPR91 radiotracers within the series.

Microwave-Assisted Synthesis of Novel Pyrazolo[3,4-g][1,8]naphthyridin-5-amine with Potential Antifungal and Antitumor Activity

The microwave assisted reaction between heterocyclic o-aminonitriles 1 and cyclic ketones 2 catalyzed by zinc chloride led to new series of pyrazolo[3,4-b][1,8]naphthyridin-5-amines 3 in good yields. This procedure provides several advantages such as being environmentally friendly, high yields, simple work-up procedure, broad scope of applicability and the protocol provides an alternative for the synthesis of pyrazolonaphthyridines. The whole series showed antifungal activities against Candida albicans and Cryptococcus neoformans standardized strains, being compounds with a 4-p-tolyl substituent of the naphthyridin scheleton (3a, 3d and 3g), the most active ones mainly against C. albicans, which appear to be related to their comparative hydrophobicity. Among them, 3d, containing a cyclohexyl fused ring, showed the best activity. The anti-Candida activity was corroborated by testing the three most active compounds against clinical isolates of albicans and non-albicans Candida strains. These compounds were also screened by the US National Cancer Institute (NCI) for their ability to inhibit 60 different human tumor cell lines. Compounds 3a and 3e showed remarkable antitumor activity against cancer cell lines, with the most important GI₅₀ values ranging from 0.62 to 2.18 μM.

Comparative pharmacokinetics and bioavailability of gemifloxacin administered as an intravenous 200 mg formulation or an oral 320 mg tablet

BACKGROUND

Gemifloxacin is a synthetic fluoroquinolone antimicrobial agent, which has potent activity against most Gram-negative and Gram-positive organisms. It is indicated for the treatment of community-acquired pneumonia and acute bacterial exacerbation of chronic bronchitis.

OBJECTIVE

The aim of this study was to assess the clinical potential of a new gemifloxacin 200 mg intravenous formulation by comparing its pharmacokinetic characteristics with those of the branded Factive(®) gemifloxacin tablet.

METHODS

A single-dose, open-label, randomized-sequence, two-period crossover study was performed with 17 healthy male volunteers. The two treatment periods were separated by a 1-week washout period. Blood samples were taken for up to 48 h post-dose. Plasma gemifloxacin concentrations were determined by a validated high-performance liquid chromatography-tandem mass spectrometry method. To calculate the pharmacokinetic parameters, noncompartmental analysis was performed. The two formulations were considered to be pharmacokinetically equivalent if the 90 % confidence intervals (CIs) of the log-transformed ratios (intravenous/oral formulations) of the area under the plasma concentration-time curve (AUC) from time zero to the time of the last measurable concentration (AUClast) and the AUC from time zero to infinity (AUC∞) were within the standard bioequivalence range (0.8-1.25). Safety and tolerability were evaluated on the basis of physical examinations, vital signs, electrocardiograms, clinical laboratory tests and adverse event monitoring.

RESULTS

Seventeen subjects were enrolled, and 15 subjects completed the study. Sixteen subjects received intravenous 200 mg gemifloxacin and 15 received oral 320 mg gemifloxacin. The 15 subjects in the pharmacokinetic analysis set had a mean (standard deviation [SD]) age, height and weight of 27.2 (5.3) years, 173.5 (4.4) cm and 67.3 (7.4) kg, respectively. Both formulations had similar pharmacokinetic profiles. For the intravenous formulation, the mean (SD) AUClast, AUC∞ and maximum plasma concentration (C max) values were 9.12 (4.03) μg·h/mL, 9.26 (4.07) μg·h/mL and 2.90 (1.65) μg/mL, respectively, while these values for the oral formulation were 9.44 (3.34) μg·h/mL, 9.60 (3.49) μg·h/mL and 2.03 (0.95) μg/mL, respectively. For the intravenous and oral formulations, the median (range) time to reach C max (t max) values were 0.9 (0.7-1.0) and 1.0 (0.5-2.0) h, respectively. The mean relative bioavailability was 68.99 %. The 90 % CI of the ratios of the log-transformed values of AUClast and AUC∞ was 0.82-1.07. There were no serious adverse events. The intravenous and oral formulations were associated with treatment-emergent adverse event incidences of 63 % (10/16) and 13 % (2/15), respectively. After the intravenous formulation was administered, application site pain and paraesthesia were the most frequently reported adverse events (31 and 25 %, respectively). All adverse events resolved spontaneously without treatment.

CONCLUSION

Intravenous 200 mg and oral 320 mg formulations of gemifloxacin are equivalent in terms of AUC following a single dose in healthy male subjects.

Short-Course Therapy of Gemifloxacin Effective Against Pneumococcal Pneumonia in Mice

Standard 7-14 day (d) courses of antimicrobial therapy for community-acquired pneumonia (CAP) are thought to have contributed to the emergence of resistant pneumoccoci. Consequently, short-course fluoroquinolone regimens have been proposed to minimize resistance. To test this, we examined 2-day versus 5-day regimens of gemifloxacin and levofloxacin for treatment of pneumonia in a murine model. In doing so, we also investigated whether the enhanced potency of gemifloxacin would influence outcomes. CD1 Swiss mice were infected intratracheally with 10(5)-CFU of a virulent Streptococcus pneumoniae strain. Drugs were administered every 8 h for 2 d and 5 d, starting at 24 h postinfection. Temperature was used to assess disease progression. Gemifloxacin remained effective for 2 d and 5 d, with survival rates of 100%-83% compared with 40%-58% for levofloxacin. Eighty-nine to 100% of gemifloxacin-treated mice were clear of pulmonary bacteria compared with only 0%-20% for levofloxacin. For levofloxacin-treated mice, 2 of 7 (29%) isolates with a levofloxacin minimum inhibitory concentration (MIC) 4 times that of the infecting parent strain had ParC mutations. By contrast, no isolates recovered from gemifloxacin-treated mice were reduced in susceptibility. Gemifloxacin could be effective in shortening duration of therapy for CAP treatment as well as minimize resistance development.

Feasibility of multiphoton microscopy-based quantification of antibiotic uptake into neutrophil granulocytes

Antibiotic levels in livestock are usually evaluated through destructive analysis. Taking advantage of the fluorescent properties of marbofloxacin (MBX) and trovafloxacin (TVX), multiphoton microscopy (MPM) was evaluated as a minimally invasive and nondestructive method to determine the penetration of TVX and MBX into sheep neutrophils. Standard curves were measured with drug-only solutions and suggested that MBX was more suited for this type of analysis. The intracellular concentration of both TVX and MBX was higher than the extracellular concentration after incubating neutrophils for 30 min at concentrations ranging from 0.1 to 100  μg/ml for both the drugs. The intracellular concentration of TVX increased with the extracellular concentration but was always greater than the extracellular concentration, suggesting active internalization. On the other hand, intracellular/extracellular ratio (I/E) peaked at 1.6-fold I/E for 1  μg/ml and then gradually decreased with increased concentration to 1.2-fold I/E at 100  μg/ml. For the first time, this study showed the use of MPM to quantify antibiotic uptake by sheep neutrophils and observed that both antibiotics were taken up by sheep neutrophils beyond extracellular levels.

Drug-drug interaction analysis of pyronaridine/artesunate and ritonavir in healthy volunteers

A multiple dose, parallel group study was conducted to assess for a drug-drug interaction between the pyronaridine/artesunate (PA) combination antimalarial and ritonavir. Thirty-four healthy adults were randomized (1:1) to receive PA for 3 days or PA with ritonavir (100 mg twice daily for 17 days, PA administered on Days 8–10). Pharmacokinetic parameters for pyronaridine, artesunate, and its active metabolite dihydroartemisinin (DHA) were obtained after the last PA dose and for ritonavir on Days 1 and 10. Ritonavir coadministration did not markedly change pyronaridine pharmacokinetics but resulted in a 27% increase in artesunate area under the curve (AUC) and a 38% decrease in DHA AUC. Ritonavir exposure was increased 3.2-fold in the presence of PA. The only relevant safety observations were increases in liver enzymes, only reaching a clinically significant grade in the PA + ritonavir arm. It was concluded that coadministered ritonavir and PA interact to alter exposure to artesunate, DHA, and ritonavir itself.

6-Benzylamino 4-oxo-1,4-dihydro-1,8-naphthyridines and 4-oxo-1,4-dihydroquinolines as HIV integrase inhibitors

SAR studies on the quinolone carboxylic acid class of HIV-1 integrase inhibitors focused on improving the metabolic stability and led to the discovery of 27 and 38.

Gemifloxacin use in the treatment of acute bacterial exacerbation of chronic bronchitis

The newest generation of fluoroquinolones have proven efficacy against bacterial organisms associated with acute exacerbation of chronic bronchitis (AECB). Gemifloxacin, as one of the quinolones in this class, exhibits many of the pharmacokinetic and pharmacodynamic characteristics of the class with a few notable differences. Against Streptococccus pneumoniae it has a lower minimal inhibitory concentration (MIC) than the other respiratory fluoroquinolones and it has activity against both bacterial DNA gyrase and topoisomerase IV. The increased activity of gemifloxacin against both enzymes may be associated with decreased rates of resistance. Clinically, gemifloxacin has been shown to have positive effects on length of hospitalization and increased success at long-term follow-up in AECB patients. These associations were observed in noninferiority comparison studies. Although an advantage with the use of gemifloxacin in AECB is suggested, there are no comparison data is available to conclude that gemifloxacin is superior to the other respiratory fluoroquinolones. Gemifloxacin is generally well tolerated, but is associated with a characteristic rash and gastrointestinal upset as its most common observed side effects.

Electrophysiological Safety of Novel Fluoroquinolone Antibiotic Agents Gemifloxacin and Balofloxacin

Some fluoroquinolones have been reported to induce QT interval prolongation associated with the onset of torsades de pointes (TdP), resulting in a life-threatening ventricular arrhythmia. We investigated the cardiac electrophysiological effects of two new fluoroquinolones, gemifloxacin and balofloxacin, by using conventional microelectrode recording techniques in isolated rabbit Purkinje fiber and whole-cell patch-clamp techniques in human ether-á-go-go related gene (hERG)-transient transfected CHO cells. Gemifloxacin had no significant effects on the resting membrane potential, total amplitude, action potential, and Vmax of phase 0 depolarization at concentrations up to 30 microM, but gemifloxacin at 100 microM significantly decreased total amplitude (p < 0.01). These values of gemifloxacin (30 and 100 microM) were approximately 25- and 83-fold more than the free plasma concentration of 1.2 microM in a single therapeutic injection in humans. For I(hERG), the IC(50) value was about 300 microM. Balofloxacin had also no significant effects on the resting membrane potential, total amplitude, action potential duration, and Vmax of phase 0 depolarization at concentrations up to 30 microM, but balofloxacin at 100 microM significantly (p < 0.01) prolonged action potentials at both 50% repolarization (APD(50)) and 90% repolarization (APD(90)). These values of balofloxacin (30 and 100 microM) were approximately 6.8- and 23-fold more than the free plasma concentration of 4.4 microM in a single therapeutic injection in humans. For I(hERG), the IC(50) value was 214 +/- 14 microM. Therefore, our data suggested that in the electrophysiological aspect, gemifloxacin and balofloxacin may have no torsadogenic potenties up to 30 microM.

Renal elimination of a novel and potent αvβ3integrin antagonist in animals

Compound A (3-{2-oxo-3-[3-(5,6,7,8-tetrahydro-[1,8]napthyridin-2-yl)propyl]-imidazolidin-1-yl}-3(S)-(6-methoxy-pyridin-3-yl)propionic acid), a hydrophilic zwitter-ion, is a potent and selective alphavbeta3 integrin antagonist currently under clinical development for the treatment of osteoporosis. The mechanism of renal excretion of compound A was investigated using a combination of in vivo and in vitro approaches. In rats, renal excretion of compound A involved tubular secretion; ratios between renal clearance, corrected for unbound fraction in plasma (CLr,u) and glomerular filtration rate (GFR) were greater than unity (2-5). The tubular secretion of compound A was saturable at high plasma levels (> 26 microM), and was inhibited significantly, although modestly (about twofold) by relatively high plasma concentrations of the organic anion PAH (160 microM) and the cation cimetidine (about 400 microM), but not by the P-gp inhibitor quinidine (about 50 microM). However, compound A (about 100 microM) had a minimal effect on CLr/GFRs for cimetidine and PAH. In rhesus monkeys, renal elimination of compound A also involved tubular secretion, with a CLr,u/GFR ratio of about 30. The renal secretion of compound A was not affected by either cimetidine (about 120 microM) or PAH (about 80 microM). Similarly, compound A (about 40 microM) had a minimal effect on the renal tubular secretion of both cimetidine and PAH. At the doses studied, neither rat nor monkey plasma protein binding of compound A, cimetidine or PAH was affected in the presence of each other. In vitro transport studies showed that compound A was not a substrate for P-gp in the Caco-2, human MDR1 and mouse mdr1a transfected LLC-PK1 cell lines. In an uptake study using rOAT1 and rOAT3 transfected HEK cell lines, compound A was shown to be a substrate for rat OAT3 (Km= 15 microM), but not rat OAT1. The results suggest that the tubular secretion of compound A is not mediated by P-gp, but rather is mediated, at least in part, via the organic anion transporter OAT3, the renal transporter shown to be capable of transporting both the organic anion PAH and the organic cation cimetidine. Although there is a possibility for pharmacokinetic interactions between compound A and substrates or inhibitors of OAT3, at the renal excretion level, the magnitude of interaction would likely be modest in humans at clinically relevant doses.

SNS-595, a naphthyridine cell cycle inhibitor and stimulator of apoptosis for the treatment of cancers

Sunesis Pharmaceuticals Inc, under license from Dainippon Sumitomo Pharma Co Ltd, is developing SNS-595, a naphthyridine cell cycle inhibitor and apoptosis stimulator, for the potential treatment of a variety of solid and hematological malignancies. Phase I clinical trials had been completed in several solid tumor types and phase II clinical trials had been completed in patients with small-cell lung cancer and NSCLC. A phase II clinical trial in patients with platinum-resistant ovarian cancer and phase I/II and phase II clinical trials in patients with acute leukemias were ongoing at the time of publication.

A potent and orally active HIV-1 integrase inhibitor

A 1,6-naphthyridine inhibitor of HIV-1 integrase has been discovered with excellent inhibitory activity in cells, good pharmacokinetics, and an excellent ability to inhibit virus with mutant enzyme.

[Evaluation of efficacy of oral quinolone against Streptococcus pneumoniae AND Haemophilus influenzae with the use of Monte Carlo simulation]

We investigated the efficacies of various administration methods for levofloxacin (LVFX) and tosufloxacin (TFLX) against 161 isolates of Streptococcus pneumoniae and 309 isolates of Haemophilus influenzae isolated in Gifu prefecture, using Monte Carlo simulation. The pharmacokinetic parameters of the fluoroquinolones were calculated from changes in blood concentration in healthy adults. Monte Carlo simulation was performed for 1,000 times to determine the AUC/MIC target attainment rates for various administration methods for fluoroquinolones (LVFX: 100 mgx3, 200 mgx2, 500 mgx 1, TFLX: 150 mgx3, 300 mgx2) with Crystal Ball 7. For S. pneumoniae, target attainment rates ofAUC/MIC; 30 were 47.18%, 75.54%, 89.16%, 93.63% and 98.63% for LVFX 100mgx3, LVFX 200mgx2, LVFX 500mgxl, TFLX 150mgx3 and TFLX 300mgx2, respectively. For H. influenzae, target attainment rates of AUC/MIC; 125 were 99.20%, 99.05%, 99.54%, 99.66% and 100% for LVFX 100mgx3, LVFX 200mgx2, LVFX 500mgxl, TFLX 150mgx3 and TFLX 300mgx2, respectively. These results suggest that administration methods might have a large impact on the efficacy of treatment with oral fluoroquinolones, and to determine administration method based on PK/PD would be important in clinical practices.

p38 MAP kinase inhibitors. Part 5: Discovery of an orally bio-available and highly efficacious compound based on the 7-amino-naphthyridone scaffold

A new sub-class of p38 inhibitors represented by 7-amino-naphthyridone have been discovered. Benchmark compound 16 potently inhibited p38 in vitro, was functionally active, and displayed excellent pharmacokinetic profiles in two animal species. Compound 16 reduced inflammation in animal disease models at EC(50) doses as low as 0.2mpk.

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.

Gemifloxacin: effects of sub-inhibitory concentrations on various factors affecting bacterial virulence

This study investigated the ability of sub-MICs of gemifloxacin to interfere with the bacterial virulence parameters of adhesiveness, haemagglutination, hydrophobicity and motility, as well as their interactions with host neutrophilic defences such as phagocytosis, killing and respiratory bursts. The adhesiveness of both Escherichia coli and Staphylococcus aureus was significantly reduced to a subinhibitory concentration of 1/32 MIC. Indirect fimbriation parameters, such as hydrophobicity and haemagglutination were significantly reduced at a concentration of 1/8 MIC, as was migration (swarming). Phagocytosis and the respiratory burst measured by means of chemiluminescence were not affected, but killing was significantly increased from 1/2 to 1/8 MIC. The interpolation of these pharmacodynamic findings with pharmacokinetic curves indicates that sub-MIC concentrations of gemifloxacin can prolong antimicrobial effects on virulence determinants up to 27 h after the antimicrobial concentration has fallen below the MIC value.

Mechanism of fluoroquinolone resistance is an important factor in determining the antimicrobial effect of gemifloxacin against Streptococcus pneumoniae in an in vitro pharmacokinetic model

Antibacterial effect and emergence of resistance to gemifloxacin and levofloxacin were studied in an in vitro pharmacokinetic model of infection. A panel of Streptococcus pneumoniae strains with known mechanisms of resistance were used; two strains had no known resistance mechanism, two had efflux pumps, three had gyrA plus parC mutations, and one had only a parC mutation. Gemifloxacin MICs were in the range of 0.016 to 0.25 mg/liter, and levofloxacin MICs ranged from 1 to 16 mg/liter. Antimicrobial effect was measured by area under the bacterial-kill curve up to 72 h, and emergence of resistance was determined by population analysis profile before and during drug exposure. The area under the curve (AUC)/MIC ratios for gemifloxacin and levofloxacin were 35 to 544 and 3 to 48, respectively. As expected on the basis of these AUC/MIC ratio differences, antibacterial effect was much greater for gemifloxacin than levofloxacin. In the gemifloxacin simulations, mechanism of resistance as well as MIC determined the antibacterial effect, as indicated by gemifloxacin's greater effect against efflux strains compared to those with gyrA or parC mutations despite similar MICs. This was not true of levofloxacin. Emergence of resistance was not easily demonstrated with either agent, and mechanism of resistance did not have any impact on it.