Preclinical safety evaluation of moxifloxacin, a novel fluoroquinolone

Preclinical safety evaluation of levonadifloxacin, a novel anti-methicillin-resistant Staphyloccocus aureus benzoquinolizine fluoroquinolone by intravenous and oral administration

Fluoroquinolone (FQ) antibacterials have drawn heightened attention from various international regulatory agencies due to their class-specific side effects. Levonadifloxacin is a novel broad spectrum benzoquinolizine FQ active against methicillin-resistant Staphyloccocus aureus (MRSA). Owing to FQ-associated safety concerns, extensive preclinical safety pharmacology (central nervous system and cardiac safety) and toxicology studies (subacute repeat-dose toxicity, genotoxicity, phototoxicity and chondrotoxicity) of levonadifloxacin were performed at relatively high doses. Intravenous (IV) and oral studies were conducted using WCK 771 (l-arginine salt of levonadifloxacin) and WCK 2349 (l-alanine ester prodrug of levonadifloxacin), respectively. Safety pharmacology studies following single dose revealed no adverse effects on central nervous system (including seizure) in mice and cardiovascular system (hERG and monkey telemetry). In repeat-dose toxicity studies, except for IV bolus dosing related effects in rat (hyperactivity, mild convulsion, polypnoea and injection site irritation) and dog (emesis and salivation), no other adverse findings limiting the dosing duration were observed. No major biochemical, haematological, gross or histopathological changes suggestive of damage to vital organs were observed in either WCK 771- or WCK 2349-treated groups. WCK 771 and WCK 2349 were found to be nongenotoxic; however, they showed weak phototoxicity that was comparable with levofloxacin. WCK 771 showed chondrotoxicity in the Beagle dog pups on repeat-dose administration; however, the severity level was lower than ofloxacin. Overall, preclinical safety studies helped establish wider safety margin for WCK 771 and WCK 2349 that supports administration of higher therapeutic doses in humans by both IV and oral routes, thereby enabling safe anti-MRSA treatment.

A VigiBase Descriptive Study of Fluoroquinolone-Associated Peripheral Nervous System Disorders

Background: Recent drug safety concerns described fluoroquinolone (FQ)-induced peripheral nervous system reactions. The objective of this study was to characterize such reports from VigiBase. Methods: The analysis included FQ-induced peripheral nervous system disorder adverse drug reaction (ADR) reports (up to July 2019). We looked into the disproportionality data in terms of proportional reporting ratio (PRR) and information component (IC) values, and descriptive analysis was performed for FQ-ADRs positive associations (ADRs, suspected FQs, potential risk factors, such as associated therapy and underlying disease). Results: Disproportionality analysis revealed 4374 reports (3531 serious) with peripheral nervous system ADRs associated with at least three FQs (neuropathy peripheral, 5492; neuralgia, 481; polyneuropathy, 220; sensory loss, 99; peripheral sensorimotor neuropathy, 39). Among these, both time-to-onset and duration of reaction were mostly between 1–7 days and ≥30 days. Most of the ADRs were not recovered/resolved at the time of reporting. Conclusion: The results augment the existing data on FQ safety concerns, specifically their potential effect on the nervous system.

A pilot study on the comparative minimum inhibitory and mutant prevention concentration values for moxifloxacin and pradofloxacin against canine and human isolates of Staphylococcus pseudintermedius and S. schleiferi

BACKGROUND

Moxifloxacin is a fourth-generation fluoroquinolone (FQ) that is approved for use in people to treat a variety of infections. Some veterinary microbiology laboratories report moxifloxacin in culture and sensitivity profiles for Staphylococcus pseudintermedius and S. schleiferi albeit using Clinical & Laboratory Standards Institute (CLSI) breakpoints for S. aureus. Previous studies have shown that S. aureus breakpoints can mischaracterize S. pseudintermedius susceptibility to various drugs. Pradofloxacin is a third generation veterinary FQ with a similar mechanism of action and spectrum of activity to moxifloxacin; however, the dose format (25 mg/mL solution) available in the USA may limit its practical use in large dogs.

OBJECTIVE

To determine the minimum inhibitory concentration (MIC), mutant prevention concentration (MPC) and mutant selection window (MSW) of moxifloxacin and pradofloxacin for isolates of S. pseudintermedius and S. schleiferi.

METHODS AND MATERIALS

Pulsed-field gel electrophoresis was performed to establish that each bacterial isolate selected for testing represented an unique strain. The MIC, MPC and MSW for moxifloxacin and pradofloxacin were determined from 60 strains of S. pseudintermedius and seven strains of S. schleiferi.

RESULTS

The MIC and MPC ranges of moxifloxacin and pradofloxacin for meticillin-susceptible S. pseudintermedius were similar. However, MIC and MPC ranges were much wider and resistance to both drugs was more common for meticillin-resistant strains of S. pseudintermedius and S. schleiferi.

CONCLUSIONS AND CLINICAL IMPORTANCE

The narrow MSW of these drugs may reduce the risk of selecting for antibiotic-resistant subpopulations. Pharmacokinetic, pharmacodynamic and safety studies are needed.

An enhanced regimen as post-exposure chemoprophylaxis for leprosy: PEP+

The ongoing transmission of Mycobacterium (M.) leprae reflected in a very slow decline in leprosy incidence, forces us to be innovative and conduct cutting-edge research. Single dose rifampicin (SDR) as post-exposure prophylaxis (PEP) for contacts of leprosy patients, reduces their risk to develop leprosy by 60%. This is a promising new preventive measure that can be integrated into routine leprosy control programmes, as is being demonstrated in the Leprosy Post-Exposure Programme that is currently ongoing in eight countries.The limited (60%) effectiveness of SDR is likely due to the fact that some contacts have a preclinical infection beyond the early stages for which SDR is not sufficient to prevent the development of clinical signs and symptoms of leprosy. An enhanced regimen, more potent against a higher load of leprosy bacteria, would increase the effectiveness of this preventive measure significantly.The Netherlands Leprosy Relief (NLR) is developing a multi-country study aiming to show that breaking the chain of transmission of M. leprae is possible, evidenced by a dramatic reduction in incidence. In this study the assessment of the effectiveness of an enhanced prophylactic regimen for leprosy is an important component. To define the so called PEP++ regimen for this intervention study, NLR convened an Expert Meeting that was attended by clinical leprologists, public health experts, pharmacologists, dermatologists and microbiologists.The Expert Meeting advised on combinations of available drugs, with known efficacy against leprosy, as well as on the duration of the intake, aiming at a risk reduction of 80-90%. To come to a conclusion the Expert Meeting considered the bactericidal, sterilising and bacteriostatic activity of the potential drugs. The criteria used to determine an optimal enhanced regimen were: effectiveness, safety, acceptability, availability, affordability, feasibility and not inducing drug resistance.The Expert Meeting concluded that the enhanced regimen for the PEP++ study should comprise three standard doses of rifampicin 600 mg (weight adjusted when given to children) plus moxifloxacin 400 mg given at four-weekly intervals. For children and for adults with contraindications for moxifloxacin, moxifloxacin should be replaced by clarithromycin 300 mg (weight adjusted).

Gut microbiome-related metabolic changes in plasma of antibiotic-treated rats

The intestinal microbiota contributes to the metabolism of its host. Adequate identification of the microbiota's impact on the host plasma metabolites is lacking. As antibiotics have a profound effect on the microbial composition and hence on the mammalian-microbiota co-metabolism, we studied the effects of antibiotics on the "functionality of the microbiome"-defined as the production of metabolites absorbed by the host. This metabolomics study presents insights into the mammalian-microbiome co-metabolism of endogenous metabolites. To identify plasma metabolites related to microbiome changes due to antibiotic treatment, we have applied broad-spectrum antibiotics belonging to the class of aminoglycosides (neomycin, gentamicin), fluoroquinolones (moxifloxacin, levofloxacin) and tetracyclines (doxycycline, tetracycline). These were administered orally for 28 days to male rats including blood sampling for metabolic profiling after 7, 14 and 28 days. Fluoroquinolones and tetracyclines can be absorbed from the gut; whereas, aminoglycosides are poorly absorbed. Hippuric acid, indole-3-acetic acid and glycerol were identified as key metabolites affected by antibiotic treatment, beside changes mainly concerning amino acids and carbohydrates. Inter alia, effects on indole-3-propionic acid were found to be unique for aminoglycosides, and on 3-indoxylsulfate for tetracyclines. For each class of antibiotics, specific metabolome patterns could be established in the MetaMap®Tox data base, which contains metabolome data for more than 550 reference compounds. The results suggest that plasma-based metabolic profiling (metabolomics) could be a suitable tool to investigate the effect of antibiotics on the functionality of the microbiome and to obtain insight into the mammalian-microbiome co-metabolism.

Fluoroquinolones impair tendon healing in a rat rotator cuff repair model: a preliminary study

BACKGROUND

Recent studies suggest that fluoroquinolone antibiotics predispose tendons to tendinopathy and/or rupture. However, no investigations on the reparative capacity of tendons exposed to fluoroquinolones have been conducted.

HYPOTHESIS

Fluoroquinolone-treated animals will have inferior biochemical, histological, and biomechanical properties at the healing tendon-bone enthesis compared with controls.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ninety-two rats underwent rotator cuff repair and were randomly assigned to 1 of 4 groups: (1) preoperative (Preop), whereby animals received fleroxacin for 1 week preoperatively; (2) pre- and postoperative (Pre/Postop), whereby animals received fleroxacin for 1 week preoperatively and for 2 weeks postoperatively; (3) postoperative (Postop), whereby animals received fleroxacin for 2 weeks postoperatively; and (4) control, whereby animals received vehicle for 1 week preoperatively and for 2 weeks postoperatively. Rats were euthanized at 2 weeks postoperatively for biochemical, histological, and biomechanical analysis. All data were expressed as mean ± standard error of the mean (SEM). Statistical comparisons were performed using either 1-way or 2-way ANOVA, with P < .05 considered significant.

RESULTS

Reverse transcriptase quantitative polymerase chain reaction (RTqPCR) analysis revealed a 30-fold increase in expression of matrix metalloproteinase (MMP)-3, a 7-fold increase in MMP-13, and a 4-fold increase in tissue inhibitor of metalloproteinases (TIMP)-1 in the Pre/Postop group compared with the other groups. The appearance of the healing enthesis in all treated animals was qualitatively different than that in controls. The tendons were friable and atrophic. All 3 treated groups showed significantly less fibrocartilage and poorly organized collagen at the healing enthesis compared with control animals. There was a significant difference in the mode of failure, with treated animals demonstrating an intrasubstance failure of the supraspinatus tendon during testing. In contrast, only 1 of 10 control samples failed within the tendon substance. The healing enthesis of the Pre/Postop group displayed significantly reduced ultimate load to failure compared with the Preop, Postop, and control groups. There was no significant difference in load to failure in the Preop group compared with the Postop group. Pre/Postop animals demonstrated significantly reduced cross-sectional area compared with the Postop and control groups. There was also a significant reduction in area between the Preop and control groups.

CONCLUSION

In this preliminary study, fluoroquinolone treatment negatively influenced tendon healing.

CLINICAL RELEVANCE

These findings indicate that there was an active but inadequate repair response that has potential clinical implications for patients who are exposed to fluoroquinolones before tendon repair surgery.

Correlation among the toxicity profiling (28-days repeated oral dose toxicity), toxicokinetics and tissue distribution data of ulifloxacin, the active metabolite of prulifloxacin in Wistar albino rats

This experiment was designed to investigate correlation among 28-days repeated oral dose toxicity, toxicokinetics and tissue distribution data of ulifloxacin (active metabolite of prulifloxacin) in Wistar albino rats. Prulifloxacin was administered for 28-days in rats at 0, 100, 200, 400mg/kg/day followed by 14-days recovery period. Simultaneously different toxicokinetic parameters and tissue distributions of ulifloxacin was examined by LC-MS/MS method. Plasma levels and tissue concentrations of ulifloxacin were increased with dose-related manner. Ulifloxacin was also distributed to many tissues, and concentration in lungs nearly equivalent to the plasma concentration. Based on these results it was concluded that long-term repeated dose of prulifloxacin may produce different blood parameters abnormality, liver damage, stomach ulcer, joint damage and dysfunction of lungs in rats which relates to high tissue distribution and accumulation of ulifloxacin in these tissues. These findings help in management of prulifloxacin induced adverse effects by appropriate dose selection in clinical practice.

Antibiotic Treatment of Dogs and Cats during Pregnancy

The use of pharmacological agents in pregnant females poses a major clinical challenge due to the marked physiological changes that may modify the pharmacokinetics of drugs and to the potential effects on the fetus. The purpose of this paper is to review briefly our knowledge on the use of antibacterial drugs during pregnancy and to provide information for the judicious selection of an antimicrobial treatment for use in pregnant bitches and queens. The risk to the fetus is a result of the ability of a drug to reach the fetal circulation and to produce toxic effects. The placenta functions as a barrier that protects the fetus due to the presence of transporters and metabolising enzymes; however, during pregnancy, the presence and activity of both enzymes and transporters may change. Antimicrobial agents that have been shown to be safe for use during pregnancy include betalactams, macrolides, and lincosamides. Pharmacotherapy during pregnancy in all species may affect adversely the developing fetus; therefore, it should be avoided when possible.

Twenty-eight days repeated oral dose toxicity study of gemifloxacin in Wistar albino rats

The purpose of this study was to investigate the potential toxicity of gemifloxacin by 28-day repeated oral dose in Wistar albino rats. The test article, was administered daily by gavage to male and female rats at dose levels of 0, 50, 100, 200 mg/kg/day. At the end of treatment period, 12 rats/sex/group was sacrificed, while six extra rats/sex in the vehicle control and highest dose groups sacrificed after 14 days recovery period. During the treatment and recovery periods, clinical signs, mortality, body weights, food and water consumption, ophthalmoscopy, urinalysis, phototoxicity, hematology, serum biochemistry, synovial fluid biochemistry, electrocardiogram (ECG), gross findings, organ weights, microscopic examination of synovial fluid, and histopathology were examined. Hematological and serum biochemical investigations revealed a dose-dependent increase in the total white blood cell (WBC), total bilirubin (T-BIL), glucose (GLU), alanine aminotransferase (ALT) and significant decreases in total protein (TP) were observed in both sexes at the same dose, at the end of treatment period, but the levels returned toward normal during the recovery period. Histopathology of talar joint showed that erosion of the articular surface of that joint in both sexes at the end of treatment period at the dose level of 200 mg/kg/day. Degenerative changes in tendinocytes were observed in Achilles tendon of both sexes at the high dose level at the end of treatment period. In histopathological study shows partial effacement of liver architecture and focal ulceration in gastric mucosa at the high dose level at the end of treatment period. Based on these results, it was concluded that 28 days repeated oral dose of gemifloxacin caused increases in the liver weight, WBC count, T-BIL, glucose level, ALT, decreasing the TP, cause chronic hepatitis and acute gastritis, erosion of the articular surface of joint and histopathologic changes in Achilles tendon in rats at the dose level of 200 mg/kg/day.

Early toxicology signal generation in the mouse

The rat has been the preferred rodent toxicology species since before regulatory requirements have been in place, and there exists in the pharmaceutical industry and the regulatory agencies a significant amount of historical data for the rat. The resulting experience base with the rat makes the possibility of replacing it with the mouse for regulated toxicology studies untenable for all but the most extreme circumstances. However, toxicologists are very familiar with the mouse as a model for chronic carcinogenicity studies, and there exist multiple preclinical mouse models of disease. The authors evaluated the use of the mouse for early in vivo toxicology signal generation and prioritization of small molecule lead compounds prior to nomination of a development candidate. In five-day oral gavage studies with three test agents in the mouse, the authors were able to identify the same dose-limiting toxicities as those identified in the rat, including examples of compound-mediated hemolysis as well as microscopic lesions in the alimentary canal, kidney, and pancreas. Performing early signal generation studies in the mouse allows for earlier assessment of the safety liabilities of small molecules, requires significantly less compound, and allows evaluation of more compounds earlier in the project's life cycle.

Effects of moxifloxacin and clinafloxacin on murine limb buds cultured in regular and in magnesium-deficient medium

Evaluation of the prenatal toxicity of a substance in rats or other animals according to the current guidelines is often hampered by the rapid metabolism of the test compound and/or by maternal toxicity. One example for such a compound is moxifloxacin. In vitro systems offer the possibility to study the direct effects of the test compound on embryonic tissues. The aim of this study was to evaluate the embryotoxic potential of moxifloxacin in vitro using the murine limb bud culture. Clinafloxacin, which was found to be teratogenic when tested in rats, was used for comparison. The effects of various concentrations of moxifloxacin (10, 30, 60 and 100 mg/L) and clinafloxacin (3, 10 and 30 mg/L) on growth and differentiation of 12-day-old murine limb buds were studied in a standard and in a magnesium-deficient medium. After termination of the culture, the respective front limb buds were examined by different methods. Clinafloxacin showed clear-cut effects at a concentration of 30 mg/L in both media. Effects were similarly pronounced as the effects observed with moxifloxacin at a concentration of 100 mg/L. Lower concentrations of moxifloxacin, which are achieved during therapy in humans, did not impair growth and differentiation of limb buds. Using electron microscopy, slight ultrastructural changes could be seen after exposure to 3 mg clinafloxacin/L medium. Ultrastructurally, clinafloxacin caused a concentration-dependent decrease of the extracellular matrix, swelling of cell organelles and at higher concentrations necrotic chondrocytes. These effects were significantly enhanced in a magnesium-deficient medium. In conclusion, the effects of moxifloxacin on murine limb buds in vitro were definitely less pronounced than those of clinafloxacin. Effects on growth and differentiation occurred with moxifloxacin only at concentrations that are higher than plasma concentrations observed during therapy. This result is of special interest, because due to rapid metabolism of moxifloxacin in rats results from a routinely performed segment II type study cannot be used for a risk assessment.

Beau's Lines in a Patient Treated with Moxifloxacin for Anaerobic Pulmonary Infection

Onychotoxicity of fluoroquinolones is a rare event. Previously described cases of fluoroquinolone-related nail disorders were due to onychophototoxicity. This report presents a case of nail toxicity after treatment with moxifloxacin for anaerobic pulmonary infection, which has not been described previously. The appearance and circumstances of this nail disorder were consistent with the diagnosis of Beau's lines.

Moxifloxacin-based triple therapy versus clarithromycin-based triple therapy for first-line treatment of Helicobacter pylori infection: a meta-analysis of randomized controlled trials

BACKGROUND

Moxifloxacin-based triple therapy has been suggested as an alternative first line therapy to clarithromycin-based triple therapy for Helicobacter pylori infection.

AIMS

To systematically review the efficacy and tolerance of moxifloxacin-based triple therapy, and to conduct a meta-analysis of studies comparing this regimen with clarithromycin-based triple therapy.

METHODS

A search of The Cochrane Library, PUBMED, EMBASE, EBM Review databases, Science Citation Index Expanded, and CMB (Chinese Biomedical Literature Database) was performed. Randomized controlled trials comparing moxifloxacin-based triple therapy to gold standard triple therapy in the first-line treatment of Helicobacter pylori infection were selected for meta-analysis. Relative risk was used as a measure of the effect of the two above-mentioned regimens with a fixed-effects model using the methods of DerSimonian and Laird.

RESULTS

Four randomized controlled trials totaling 772 patients were included. The meta-analysis showed that the mean eradication rate was 84.1 (318/378) in the moxifloxacin-based triple therapy group and 73.6 (290/394) in the clarithromycin-based triple therapy group; there was statistical significance between the two groups (RR, 1.13; 95% CI, 1.01, 1.27; P=0.04). There were no statistically significant difference in the overall side effects (RR, 0.61; 95% CI, 0.25, 1.48; P<0.28).

CONCLUSIONS

Moxifloxacin-based triple therapy is more effective and does not increase the incidence of overall side effects compared to clarithromycin-based triple therapy in the treatment of H. pylori infection.

High eradication rate of H. pylori with moxifloxacin-based treatment: a randomized controlled trial

INTRODUCTION

Eradication of Helicobacter pylori remains a problematic treatment issue in clinical practice. The intention is to find a treatment that achieves a high rate of eradication at a low price and treatment options that are now used give us the opportunity to achieve this goal. Recently published results showing a low rate of resistance and better compliance with moxifloxacin-based treatment regimens indicate the need to investigate its efficacy in H. pylori eradication. This study is based on proving the efficacy of moxifloxacin in H. pylori eradication within the triple therapy.

AIMS AND METHODS

The aim of the study was to compare the efficacy of one week of moxifloxacin-based treatment with the standard treatment for H. pylori eradication. Patients with H. pylori infection and non-ulcer dyspepsia (n = 277) were randomly divided into four groups to receive: moxifloxacin 400 mg/d, metronidazole 400 mg twice daily, lansoprazole 30 mg twice daily (MML group); moxifloxacin 400 mg/d, amoxicillin 1 g twice daily, lansoprazole 30 mg twice daily (MAL group); clarithromycin 500 mg twice daily, metronidazole 400 mg twice daily, lansoprazole 30 mg twice daily (CML group); clarithromycin 500 mg twice daily, amoxicillin 1 g twice daily, lansoprazole 30 mg twice daily (CAL group). The patients were assessed for prevalence of H. pylori using the CLO test, histology and culture on gastric biopsy samples obtained during upper gastrointestinal endoscopy before randomization and 4-6 weeks after completion of treatment. Bacterial sensitivity to clarithromycin and moxifloxacin was determined with the E-test.

RESULTS

265 (95.6%) patients completed the study forming the basis for PP analysis. Eradication rates of H. pylori in ITT and in PP analyses were: in the MML group 93.5% (58/62) and 96.7% (58/60), respectively; in the MAL group 86.4% (57/66) and 90.5% (57/63); in the CML group 70.4% (50/71) and 75.8% (50/66); and in the CAL group 78.2% (61/78) and 80.2% (61/76). Moxifloxacin treatment protocols were significantly more effective on both ITT and PP analyses than the clarithromycin based protocols with only one exception (MAL vs. CAL on ITT analysis). Among 238 patients (86% of the entire study group), strains showing primary resistance to clarithromycin were found in 10.8% and to moxifloxacin in 5.9%. Eradication of moxifloxacin sensitive/resistant strains was 98.1%/75% for MML (p < 0.01) and 91.1%/66.7% for MAL (p = n.s.); comparison of eradication of sensitive strains in MML and MAL regimens was 98.1%/91.1% (p < 0.05), and for resistant strains 75%/66.7% (p = n.s.). CML and CAL protocols did not differ in efficacy of eradication of clarithromycin sensitive or resistant strains.

CONCLUSION

Moxifloxacin-based triple therapies showed higher eradication rates with few side effects and good drug compliance when compared with standard H. pylori treatments. Moreover, the increased prevalence of clarithromycin resistance suggests that moxifloxacin-based regimens could be safe and effective options in treatment of H. pylori infection.

Moxifloxacin, ofloxacin, sparfloxacin, and ciprofloxacin against Mycobacterium tuberculosis: evaluation of in vitro and pharmacodynamic indices that best predict in vivo efficacy

Members of the fluoroquinolone class are being actively evaluated for inclusion in tuberculosis chemotherapy regimens, and we sought to determine the best in vitro and pharmacodynamic predictors of in vivo efficacy in mice. MICs for Mycobacterium tuberculosis H37Rv were 0.1 mg/liter (sparfloxacin [SPX]) and 0.5 mg/liter (moxifloxacin [MXF], ciprofloxacin [CIP], and ofloxacin [OFX]). The unbound fraction in the presence of murine serum was concentration dependent for MXF, OFX, SPX, and CIP. In vitro time-kill studies revealed a time-dependent effect, with the CFU reduction on day 7 similar for all four drugs. However, with a J774A.1 murine macrophage tuberculosis infection model, CIP was ineffective at up to 32x MIC. In addition, MXF, OFX, and SPX exhibited less activity than had been seen in the in vitro time-kill study. After demonstrating that the area under the concentration-time curve (AUC) and maximum concentration of drug in plasma were proportional to the dose in vivo, dose fractionation studies with total oral doses of 37.5 to 19,200 mg/kg of body weight (MXF), 225 to 115,200 mg/kg (OFX), 30 to 50,000 mg/kg (SPX), and 38 to 100,000 mg/kg (CIP) were performed with a murine aerosol infection model. MXF was the most efficacious agent (3.0+/-0.2 log10 CFU/lung reduction), followed by SPX (1.4+/-0.1) and OFX (1.5+/-0.1). CIP showed no effect. The ratio of the AUC to the MIC was the pharmacodynamic parameter that best described the in vivo efficacy. In summary, a lack of intracellular killing predicted the lack of in vivo activity of CIP. The in vivo rank order for maximal efficacy of the three active fluoroquinolones was not clearly predicted by the in vitro assays, however.

Safety of Moxifloxacin as Shown in Animal and In Vitro Studies

Topical treatment of ocular bacterial infection is practiced widely, and the choice of the antibacterial agent depends on the nature of the infection, including the susceptibility of the organism, the tissue affected, and the safety profile of the agent. Moxifloxacin is a fourth-generation fluoroquinolone approved for ophthalmic use as moxifloxacin ophthalmic solution 0.5% (VIGAMOX, Alcon, Fort Worth, TX). Moxifloxacin ophthalmic solution 0.5% is self-preserved at a near-neutral pH of 6.8. In treating ocular infection, the three important aspects of therapeutic control are potency, penetration of the drug to the target site, and safety of the drug and the drug product. Moxifloxacin ophthalmic solution 0.5% provides antibacterial potency and high penetration of target ocular tissues. The ocular and systemic safety profile of moxifloxacin compares favorably with those of other fluoroquinolone antimicrobial agents, with a low risk of recognized quinolone-related toxicity. In vitro studies of fluoroquinolones with human or rabbit corneal epithelial cells or keratocytes suggest that moxifloxacin is similar in cytotoxicity potential to other drugs of this family. Specialized in vivo corneal wound-healing studies draw little distinction between moxifloxacin-treated eyes and those treated with other fluoroquinolones. Repeated-dose topical ocular studies in rabbits and monkeys, with high concentrations (up to 3%) of moxifloxacin and at treatment durations and regimens well in excess of label-prescribed use, demonstrated a high safety margin for ocular and extraocular tissues. Cornea, the tissue with highest exposure, was found to be unaffected by these high exposures, with slit-lamp biomicroscopy, corneal thickness measurement, intraocular pressure, and specular microscopy of the corneal endothelium (monkeys only), and histologic evaluation showing no effects, as compared with controls. Moxifloxacin ophthalmic solution 0.5% affords superior efficacy and ocular tissue penetration, with a favorable safety profile.

Intracameral Vigamox (moxifloxacin 0.5%) is non-toxic and effective in preventing endophthalmitis in a rabbit model

PURPOSE

To determine whether Vigamox (moxifloxacin 0.5% ophthalmic solution) can be safely injected intracamerally to prevent Staphylococcus aureus endophthalmitis in a rabbit model.

DESIGN

Animal study.

METHODS

The safety and bactericidal-effectiveness of Vigamox were evaluated in three stages using 189 New Zealand White rabbits. (Stage 1) The toxicity of two intravitreal doses of Vigamox (moxifloxacin 500, 250 microg) was compared with vancomycin (1 mg) and saline. (Stage 2) A reproducible rabbit model of Staphylococcus aureus endophthalmitis was established. (Stage 3) The bactericidal effect of intracameral Vigamox (moxifloxacin 500, 250, 125, 50 microg) was compared with vancomycin (1 mg) and saline. Intracameral antibiotic therapy commenced immediately after Staphylococcus aureus intravitreal challenge (5000 cfu). Toxicity was evaluated by masked clinical examination using a slit-lamp, an indirect ophthalmoscope, and corneal-ultrasound pachymetry. The clinical examination included the exterior eye, cornea, anterior chamber, vitreous, and retina. The presentations were graded on a severity scale of 0, 0.5, 1, 2, and 3. The bactericidal efficacy was determined using intracameral colony counts.

RESULTS

In the toxicity studies without bacterial challenge, the clinical scores of rabbits injected intracamerally with Vigamox were statistically equivalent to rabbits given intracameral vancomycin or saline. In the efficacy studies, eyes treated intravitreally with Vigamox, at all doses, or vancomycin were negative for Staphylococcus aureus and nontreated controls remained culture-positive.

CONCLUSIONS

Vigamox appears to be nontoxic for intracameral injection and effective in preventing experimental endophthalmitis in the rabbit model. Further studies will determine the clinical role of intracameral Vigamox for surgical prophylaxis and postoperative therapy.

Effects of moxifloxacin on QT interval in conscious dogs

Moxifloxacin has been shown to induce QT prolongation in both clinical and preclinical models. However, the ability to observe this effect at clinically relevant concentration in normal conscious dogs has not been reported. The purpose of this study was to investigate the effects of moxifloxacin on the QT interval in conscious, healthy dogs. Four male mongrel dogs were chronically instrumented for the measurement of arterial blood pressure, left ventricular blood pressure, cardiac output, electrocardiograms (ECGs), and body temperature. Animals were administered a 1-h i.v. infusion of moxifloxacin once per day via a catheter in the cephalic vein. Each dog received all doses (0, 1, 10, 25 and 50 mg/kg) in an escalating fashion. Moxifloxacin caused a statistically significant increase in arterial blood pressure at 50 mg/kg. A dose-response effect on QT and QTc prolongation was observed. A statistically significant prolongation in the QT interval was observed at 10, 25 and 50 mg/kg and a prolongation of QTc was observed at 25 and 50 mg/kg. These effects occurred at clinically relevant plasma concentrations. This study demonstrate that a study design with four dogs was sensitive enough to measure moxifloxacin-induced QT prolongation at clinically relevant plasma concentrations.

Moxifloxacin-based strategies for first-line treatment of Helicobacter pylori infection

BACKGROUND

Standard anti-Helicobacter pylori therapy may not achieve a satisfactory eradication rate. Fluoroquinolones, such as moxifloxacin, are safe and promising agents for H. pylori eradication.

AIM

To compare the efficacy of two 1-week moxifloxacin-based H. pylori eradication regimens with two standard treatments.

METHODS

Three hundred and twenty H. pylori-positive subjects were randomized into four groups to receive: moxifloxacin, amoxicillin, esomeprazole (Group MAE); moxifloxacin, tinidazole and esomeprazole (Group MTE); standard triple therapies with clarithromycin, amoxicillin and esomeprazole (Group CAE) or tinidazole (Group CTE) for 7 days. H. pylori status was re-assessed 6 weeks after the end of therapy by 13C urea breath test.

RESULTS

Three hundred and twenty patients completed the efficacy analysis per protocol; H. pylori eradication rate in group MTE was 90% (72 of 80) and 92% (72 of 78), in group MAE was 88% (70 of 80) and 89%, (70 of 79) in Group CAE was 73% (58 of 80) and 78% (58 of 74), and in Group CTE was 75% (60 of 80) and 79% (60 of 76), respectively, in intention-to-treat and in per protocol analyses. Eradication rates of moxifloxacin-based triple therapies were significantly higher than that observed using standard triple schemes. The incidence of side effects was significantly lower in moxifloxacin groups than in control groups.

CONCLUSIONS

Seven-day moxifloxacin-based triple therapies provide optimal eradication rates with a good compliance when compared with the standard triple therapy schemes.

Moxifloxacin: a review of its use in the management of bacterial infections

Moxifloxacin (Avelox) is a fluoroquinolone antibacterial with a methoxy group in the C-8 position and a bulky C-7 side chain. Moxifloxacin is approved for use in the treatment of acute exacerbations of chronic bronchitis (AECB), community-acquired pneumonia (CAP), acute bacterial sinusitis and uncomplicated skin and skin structure infections (approved indications may differ between countries). Moxifloxacin has a broad spectrum of antibacterial activity, including activity against penicillin-resistant Streptococcus pneumoniae. It achieves good tissue penetration and has a convenient once-daily administration schedule, as well as being available in both intravenous and oral formulations in some markets. Moxifloxacin has good efficacy in the treatment of patients with AECB, CAP, acute bacterial sinusitis and uncomplicated skin and skin structure infections, and is generally well tolerated. Thus, moxifloxacin is an important option in the treatment of bacterial infections.

In vivo experimental approach for the risk assessment of fluoroquinolone antibacterial agents-induced long QT syndrome

The proarrhythmic effects of fluoroquinolone antibacterial agents, sitafloxacin, gatifloxacin and moxifloxacin, were compared using three in vivo models. In the halothane-anesthetized dogs (n=5), intravenous 10-min infusion of gatifloxacin and moxifloxacin (1-3 mg/kg) prolonged the ventricular effective refractory period and the repolarization period to a similar extent, whereas sitafloxacin (1-3 mg/kg) prolonged the former only. No significant change was detected in other cardiovascular parameters. In the chronic complete atrioventricular block dogs (n=4), oral administration of 100 mg/kg of gatifloxacin (2 of 4) and moxifloxacin (3 of 4) induced torsades de pointes, which was not observed by sitafloxacin. In the alpha-chloralose-anesthetized rabbits (n=5), intravenous 20-min infusion of 60 mg/kg of gatifloxacin induced torsades de pointes (1 of 5) in the presence of methoxamine infusion, which was not observed by sitafloxacin or moxifloxacin. Thus, the halothane-anesthetized model is suitable for assessing QT prolongation, whereas the chronic complete atrioventricular block model is sensitive for detecting torsadogenic action of drugs. The alpha-chloralose-anesthetized model is the simplest and least expensive method, but its sensitivity to detect proarrhythmic action may be less great.

QT prolongation with antimicrobial agents: understanding the significance

Cardiac toxicity has been relatively uncommon within the antimicrobial class of drugs, but well described for antiarrhythmic agents and certain antihistamines. Macrolides, pentamidine and certain antimalarials were traditionally known to cause QT-interval prolongation, and now azole antifungals, fluoroquinolones and ketolides can be added to the list. Over time, advances in preclinical testing methods for QT-interval prolongation and a better understanding of its sequelae, most notably torsades de pointes (TdP), have occurred. This, combined with the fact that five drugs have been removed from the market over the last several years, in part because of QT-interval prolongation-related toxicity, has elevated the urgency surrounding early detection and characterisation methods for evaluating non-antiarrhythmic drug classes. With technological advances and accumulating literature regarding QT prolongation, it is currently difficult or overwhelming for the practising clinician to interpret these data for purposes of formulary review or for individual patient treatment decisions. Certain patients are susceptible to the effects of QT-prolonging drugs. For example, co-variates such as gender, age, electrolyte derangements, structural heart disease, end organ impairment and, perhaps most important, genetic predisposition, underlie most if not all cases of TdP. Between and within classes of drugs there are important differences that contribute to delayed repolarisation (e.g. intrinsic potency to inhibit certain cardiac ion currents or channels, and pharmacokinetics). To this end, a risk stratification scheme may be useful to rank and compare the potential for cardiotoxicity of each drug. It appears that in most published cases of antimicrobial-associated TdP, multiple risk factors are present. Macrolides in general are associated with a greater potential than other antimicrobials for causing TdP from both a pharmacodynamic and pharmacokinetic perspective. The azole antifungal agents also can be viewed as drugs that must be weighed carefully before use since they also have both pharmacodynamic and pharmacokinetic characteristics that may trigger TdP. The fluoroquinolones appear less likely to be associated with TdP from a pharmacokinetic perspective since they do not rely on cytochrome P450 (CYP) metabolism nor do they inhibit CYP enzyme isoforms, with the exception of grepafloxacin and ciprofloxacin. Nonetheless, patient selection must be carefully made for all of these drugs. For clinicians, certain responsibilities are assumed when prescribing antimicrobial therapy: (i) appropriate use to minimise resistance; and (ii) appropriate patient and drug selection to minimise adverse event potential. Incorporating information learned regarding QT interval-related adverse effects into the drug selection process may serve to minimise collateral iatrogenic toxicity.

6-Aminoquinolones: photostability, cellular distribution and phototoxicity

Three selected aminoquinolones endowed with a potent antibacterial (compounds 1 and 2) and antiviral activity (compound 3) have been evaluated for their phototoxic properties in vitro. Photostability studies of these compounds indicate that compound 3 is photostable whereas compound 1 and in particular, compound 2 are rapidly photodegraded upon UVA irradiation, yielding a toxic photoproduct. Intracellular localization of these compounds has been evaluated by means of fluorescence microscopy using tetramethylrhodamine methyl ester and acridine orange, which are specific fluorescent probes for mitochondria and lysosomes, respectively. No co-staining was observed with lysosomal stain for all the test compounds. On the contrary compound 3 was found to be specifically incorporated in mitochondria. The compounds exhibited remarkable phototoxicity in two cell culture lines: human promyelocytic leukaemia (HL-60) and human fibrosarcoma (HT-1080). The quinolone-induced photodamage was also evaluated measuring the photosensitizing cross-linking in erythrocyte ghost membranes, the strand breaks activity and oxidative damage on plasmid DNA. The results show that these derivatives are able to photoinduce crosslink of erythrocytes spectrin, whereas do not significantly photocleavage DNA directly, but single strand breaks were observed after treatment of photosensitized DNA with two base excision repair enzymes, Fpg and Endo III respectively.

Peri- and postnatal developmental toxicity of the fluoroquinolone antibacterial DW-116 in rats

DW-116 is a fluoroquinolone antibacterial developed by Dong-Wha Pharmaceutical Industry Co. The aim of this study is to determine the potential adverse effects of this chemical on pregnancy, delivery and lactation of dams and on peri- and postnatal development of F1 offspring. The test chemical was orally administered to pregnant rats from day 16 of pregnancy, through parturition and throughout the period of lactation up to weaning (postnatal day 21) at dose levels of 0, 10, 50, or 250 mg/kg/day. The progeny were examined at birth and subsequently to weaning. Mortality, body weight change, physical signs of postnatal development (pinna detachment, incisor eruption, fur development, eye opening, testis descent and vaginal opening) and behavioral function (righting reflex, negative geotaxis, grip-strength, pupillary reflex, acoustic startle response, rotating rod test, open field test and water-filled T-maze test) were evaluated. When the exposed offspring reached maturity (11 weeks old) their reproductive capacity was assessed. Maternal toxicity was observed only in the highest dose group and was limited to decreased food consumption during the late stage of pregnancy. However, this change was not observed during the lactation period. There were no adverse effects on mortality, clinical signs, body weight, necropsy findings, organ weight of dams in any treatment group. No adverse effects on the offspring were seen with the low and middle doses tested, but the highest dose increased postnatal mortality. The number of stillborn was also increased at the highest dose but the difference was not statistically significant. Meanwhile, no treatment-related effects were observed in clinical sign, developmental and behavioral landmarks and necropsy findings at any dose levels tested. There were no treatment-related effects on the mating of the F1 generation and resulting F2 offspring. The results of this study indicate that the peri- and postnatal administration of DW-116 to female rats results in an increase in postnatal mortality at a minimally maternotoxic dose, i.e., 250 mg/kg/day. Under the experimental conditions, the no-observed-adverse-effect level for peri- and postnatal developmental toxicity was considered to be 50 mg/kg/day.

Gatifloxacin and ethionamide as the foundation for therapy of tuberculosis

The use of gatifloxacin (GAT) in combination with ethionamide (ETA) with or without pyrazinamide (PZA) for a 12-week treatment period followed by an 8-week observation period was evaluated in a model of tuberculosis in mice. Mice treated with GAT at 300 mg/kg of body weight in combination with ETA (25 mg/kg) for 5 days per week had sterile lungs, whereas mice treated with GAT (100 mg/kg) and ETA (25 mg/kg) had about 10 CFU/lung; however, there was regrowth of the organisms in both groups at the end of the observation period. When PZA (450 mg/kg 5 days per week) was added to the high-dose GAT-ETA regimen, no viable mycobacteria were present after the 8-week observation period. GAT in combination with ETA and PZA has great promise for the treatment of tuberculosis.

Clinical relevance and management of drug-related QT interval prolongation

Much attention recently has focused on drugs that prolong the QT interval, potentially leading to fatal cardiac dysrhythmias (e.g., torsade de pointes). We provide a detailed review of the published evidence that supports or does not support an association between drugs and their risk of QT prolongation. The mechanism of drug-induced QT prolongation is reviewed briefly, followed by an extensive evaluation of drugs associated with QT prolongation, torsade de pointes, or both. Drugs associated with QT prolongation are identified as having definite, probable, or proposed associations. The role of the clinician in the prevention and management of QT prolongation, drug-drug interactions that may occur with agents known to affect the QT interval, and the impact of this adverse effect on the regulatory process are addressed.

26-Week repeated oral dose toxicity study of the new quinolone antibacterial DW-116 in Sprague-Dawley rats

The purpose of this study is to investigate the potential subchronic toxicity of DW-116 by a 26-week repeated oral dose in Sprague-Dawley rats. The test article, DW-116, was administered daily by gavage to male and female rats at dose levels of 0, 5, 25 and 125 mg/kg/day. At the end of the treatment period, 12 rats/sex/group were sacrificed, while six extra rats/sex in the vehicle control and highest dose groups were sacrificed after a 4-week recovery. During the test period, clinical signs, mortality, body weights, food and water consumption, ophthalmoscopy, urinalysis, hematology, serum biochemistry, gross findings, organ weights and histopathology were examined. There was no treatment-related mortality. An increase in the incidence of post-dosing salivation was observed in both sexes of the highest dose group. At the scheduled autopsy, an increase in the liver weight was observed in males of the highest dose group in a dose-dependent manner. Hematological investigations revealed a dose-dependent increase in the total white blood cell (WBC) and lymphocyte counts in males treated with the 125 mg/kg dose. Total bilirubin and alanine aminotransferase (ALT) values were also increased in males at the same dose. These effects were completely reversible during the recovery period. There were no adverse effects on body weight, food and water consumption, ophthalmoscopy, urinalysis, necropsy findings and histopathology in any treatment group. Based on these results, it was concluded that the 26-week repeated oral dose of DW-116 caused increases in the liver weight, WBC counts, total bilirubin and ALT values in males at a dose level of 125 mg/kg/day. The target organ was determined to be the liver and WBC in males, but not in females. The no-observed-adverse-effect level (NOAEL) was considered to be 25 mg/kg/day for males and 125 mg/kg/day for females.

Rapid in vivo screening of experimental drugs for tuberculosis using gamma interferon gene-disrupted mice

We have developed a rapid new in vivo method for screening experimental drugs for their activity against Mycobacterium tuberculosis by using the gamma interferon gene-disrupted (GKO) C57BL/6 mouse. Due to the rapid growth of the infection, statistical differences indicating positive efficacy of active compounds can be seen after only 8 days of treatment. To validate this model, several fluoroquinolones, including ciprofloxacin, levofloxacin, moxifloxacin, and gatifloxacin, were tested in parallel.

Bactericidal activity of increasing daily and weekly doses of moxifloxacin in murine tuberculosis

Moxifloxacin (MXF) is a new 8-methoxyquinolone with potent activity against Mycobacterium tuberculosis and a half-life of 9 to 12 h in humans. Previous in vivo studies using daily doses of 100 mg/kg of body weight have demonstrated bactericidal activity comparable to that of isoniazid (INH) in a murine model of tuberculosis (TB). Recent pharmacokinetic data suggest that MXF may have been underadministered in these studies and that a 400-mg/kg dose in mice better approximates the area under the concentration-time curve obtained in humans after a 400-mg oral dose. Therefore, the bactericidal activity of MXF in doses up to 400 mg/kg given daily or weekly for 28 days was assessed in mice infected intravenously with 5 x 10(6) CFU of M. tuberculosis. INH was used as a positive control. After 3 days of daily therapy, the CFU counts from splenic homogenates for mice treated with MXF in doses of 100 to 400 mg/kg/day were lower than those from pretreatment controls. No significant differences in CFU counts were seen when mice receiving INH or MXF at 50 mg/kg/day were compared to pretreatment controls. After 28 days of therapy, dose-dependent reductions in CFU counts in splenic homogenates were seen for daily MXF therapy. The maximum bactericidal effect was seen with daily doses of 400 mg/kg, which resulted in a reduction in CFU counts of 1 log(10) greater than that with INH treatment, although the difference was not statistically significant. CFU counts from lung homogenates after 28 days of therapy were significantly lower in all treatment groups than in untreated controls. The weekly administration of MXF in doses ranging from 50 to 400 mg/kg resulted in no significant bactericidal activity. Mice receiving daily MXF doses of 200 and 400 mg/kg/day failed to gain weight and appeared ill after 28 days of therapy, findings suggestive of drug toxicity. In conclusion, MXF has dose-dependent bactericidal activity against M. tuberculosis in the mouse when given in doses up to 400 mg/kg, where its pharmacokinetic profile better approximates that of standard human dosages. Combination regimens which take advantage of the enhanced pharmacodynamic profile of MXF at these doses have the potential to shorten the course of antituberculous therapy or allow more intermittent (i.e., once-weekly) therapy and should be evaluated in the mouse model of TB.

Mono, dual and triple moxifloxacin-based therapies for Helicobacter pylori eradication

BACKGROUND

Moxifloxacin is a broad spectrum fluoroquinolone with single daily administration, currently used, above all, for respiratory tract infections.

AIM

To compare the efficacy of different 1-week moxifloxacin-based Helicobacter pylori eradication regimens.

METHODS

One hundred and twenty H. pylori-positive subjects were randomized to receive moxifloxacin (400 mg/day), moxifloxacin (400 mg/day) and lansoprazole (30 mg/day) or moxifloxacin (400 mg/day), lansoprazole (30 mg/day) and clarithromycin (500 mg b.d.). H. pylori status was reassessed 6 weeks after the end of therapy, and both intention-to-treat and per protocol analyses were performed.

RESULTS

One hundred and nineteen of the 120 patients completed the study. H. pylori eradication was achieved in 22.5% of patients treated with moxifloxacin, in 33.3% of subjects treated with moxifloxacin and lansoprazole and in 90% of patients treated with moxifloxacin, clarithromycin and lansoprazole.

CONCLUSIONS

Mono and dual moxifloxacin-based therapies are not acceptable for H. pylori eradication; conversely, moxifloxacin-based triple therapy may be considered as a new, effective, first-line therapy option.

Effectiveness of once-weekly rifapentine and moxifloxacin regimens against Mycobacterium tuberculosis in mice

Mice infected with 1.6 x 10(7) CFU of Mycobacterium tuberculosis were treated 14 days later for 6 months with a regimen of once-weekly 10 mg of rifapentine and 75 mg of isoniazid per kg of body weight supplemented with either 150 mg of streptomycin per kg or 100 mg of moxifloxacin per kg during either both the 2-week daily initial and once-weekly continuation phases or only in the daily 2-week initial phase. On completion of treatment, all lung cultures were negative, except for three mice, each with a single colony: two whose rifapentine-isoniazid regimen was supplemented with streptomycin during the whole course of therapy and one whose rifapentine-isoniazid regimen had no initial daily phase, but was supplemented with streptomycin and moxifloxacin during the whole course of therapy. After 3 months of follow-up, positive lung cultures were obtained from 61 and 56% of mice supplemented with streptomycin during either the full course of therapy or only the daily 2-week initial phase, respectively, and 15 and 50% of mice supplemented with moxifloxacin during either the full course of therapy or only the daily 2-week initial phase, respectively. These results suggest that moxifloxacin has sterilizing activity against M. tuberculosis.

Peripheral neuropathy associated with fluoroquinolones

OBJECTIVE

To survey cases of fluoroquinolone-associated adverse events that included peripheral nervous system (PNS) symptoms posted on Internet Web sites.

METHODS

Cases were obtained with the assistance of members of Web sites formed by people sustaining fluoroquinolone-related events. Information obtained met the standards of MedWatch, and each reported case was assessed using the Naranjo probability scale.

RESULTS

In contrast to previous reports suggesting that fluoroquinolone-associated PNS events are mild and short-term, 36 of the 45 cases reported severe events that typically involved multiple organ systems. Although many newer cases are still evolving, symptoms had lasted more than three months in 71% of cases and more than one year in 58%. Onset of adverse events was usually rapid, with 15 (33%) events beginning within 24 hours of initiating treatment, 26 (58%) within 72 hours, and 38 (84%) within one week. Sixty courses of fluoroquinolones were prescribed: levofloxacin (n = 33 cases), ciprofloxacin (n = 11), ofloxacin (n = 6), lomefloxacin (n = 1), trovafloxacin (n = 1); in eight cases the same antibiotic was prescribed twice.

CONCLUSIONS

These cases suggest a possible association between fluoroquinolone antibiotics and severe, long-term adverse effects involving the PNS as well as other organ systems. The severity of these cases may reflect a different population than typically reported to drug companies or MedWatch, which often originate from healthcare providers. In contrast, Internet Web sites may provide a forum for patients experiencing adverse effects that have not resolved promptly. Further study is warranted. Meanwhile the occurrence of PNS symptoms during fluoroquinolone therapy should prompt immediate discontinuation of the agent used.

Risk assessment for antimicrobial agent-induced QTc interval prolongation and torsades de pointes

Over the past several years a multitude of new pharmaceutical agents have been released to the market. Several of them were withdrawn altogether or their use severely restricted to certain indications due to unexpected adverse events, including fatalities. Progress in developing new compounds clearly has surpassed our technology, in some cases, to measure and predict certain toxicities. Prolongation of the QT interval, which may lead to potentially life-threatening ventricular arrhythmias such as torsades de pointes, is one example. Regulatory agencies such as the Food and Drug Administration are increasing standards by which drugs are evaluated for cardiac toxicity related to QT interval prolongation. It is imperative that clinicians be knowledgeable of the risk factors for QT prolongation and avoid the use of culpable agents in patients at risk for QT prolongation.

Bacteriostatic and bactericidal activities of moxifloxacin against Coxiella burnetii

The in vitro activity of moxifloxacin against Coxiella burnetii was compared to those of pefloxacin, ofloxacin, and doxycycline. MICs of moxifloxacin ranged from 0.5 to 1 microg/ml for the Nine Mile, Priscilla, and Q212 strains. Moxifloxacin was not bactericidal against C. burnetii at 4 microg/ml.

Oxidative DNA damage: endogenous and chemically induced

A variety of types of DNA oxidation occur endogenously and mediated by xenobiotics. Certain forms are mutagenic and carcinogenic and may lead to other pathologies.

Clinical use of the fluoroquinolones

The appetite for modification to the basic quinolone nucleus has grown logarithmically since the first quinolone was employed in clinical practice. Important structural refinements have led to expanded microbiologic activity, optimal pharmacokinetics, and increased safety profiles. The practicing clinician and researcher may glean considerable information from the quinolone structure with regard to microbiologic spectra and safety before administering these agents to patients. Although some toxicities can be ominously predictable, such as with the so-called high-risk quinolones (e.g., double-halogenated and trifluorinated quinolones), clinicians must rely on animal models of toxicity and clinical trial data to discern other toxicities (e.g., Q-Tc interval prolongation). A few quinolones enjoy a relatively clean safety profile and are well tolerated (e.g., gatifloxacin, levofloxacin, ciprofloxacin). Other quinolones may be associated with significant collateral system toxicity during therapy; however, under certain conditions, albeit rare, their potential for benefit may outweigh the existing risk. Clinafloxacin, for use in the management of lung infections caused by multiply resistant B. cepacia in cystic fibrosis patients, is an example of a risk that may be outweighed by its therapeutic benefit. Because there are many treatment alternatives within the clinician's armamentarium, the obligation is to select the safest, most therapeutically effective, and most cost-effective agent that is available. In addition to increasing mortality and morbidity, the development of toxicity or an adverse event during therapy may compromise the immediate effectiveness of treatment as well as affect the cost of the patient's care significantly. With the immediate abundance of quinolones available for use, the safest, most effective, and best-tolerated agents will likely emerge as the most appropriate therapeutic choices when a quinolone is indicated.

Effects of sparfloxacin, grepafloxacin, moxifloxacin, and ciprofloxacin on cardiac action potential duration

Fluoroquinolone antibiotics have been associated with QT prolongation following administration to humans. This study compares the effects of four fluoroquinolones, sparfloxacin, grepafloxacin, moxifloxacin and ciprofloxacin on action potential duration recorded from canine isolated cardiac Purkinje fibres. Left and right ventricular Purkinje fibres were isolated from canine hearts and continuously superfused with physiological salt solution. Action potential duration at 90% repolarization was recorded via intracellular microelectrodes. Sparfloxacin, grepafloxacin, moxifloxacin and ciprofloxacin prolonged action potential duration in a concentration dependent manner. Mean concentrations causing a 15% prolongation of action potential duration recorded at a stimulation frequency of 1 Hz were: sparfloxacin 4.2+/-0.7 microg/ml; grepafloxacin 9.3+/-0.9 microg/ml; moxifloxacin 9.9+/-1.6 microg/ml and ciprofloxacin 72.8+/-26.4 microg/ml. Prolongation was inverse frequency dependent with larger increases in action potential duration occurring when the stimulation frequency was reduced to 0.5 Hz. These results indicate that effects on action potential duration vary within this class of compound. Rank order of potency was sparfloxacin > grepafloxacin = moxifloxacin > ciprofloxacin.

Test systems to identify reproductive toxicants

Experience with drugs and other xenobiotics indicates that both animal testing and epidemiological studies are necessary to provide adequate data for an estimation of risks that might be associated with exposure to a chemical substance. In this review, the pros and cons of test systems for reproductive toxicity are discussed. Usually, several studies are performed to cover the different phases of the reproductive cycle. In the preclinical development of drugs, the three so-called 'segment testing protocols' have been used for several decades now. More recently, new testing concepts have been accepted internationally which include more flexibility in implementation. Several examples of compounds with the potential for reproductive toxicity are presented in more detail in a discussion of some pitfalls of the tests for fertility (phthalates and fluoroquinolones), teratogenicity (acyclovir and protease inhibitors) and postnatal developmental toxicity (fluoroquinolones). In addition, important aspects of kinetics and metabolism as a prerequisite for a rational interpretation of results from toxicological studies are briefly discussed. In vitro assays are useful for supplementing the routinely used in vivo approaches or for studying an expected or defined effect, but they are not suitable for revealing an unknown effect of a chemical on the complex reproductive process.

Toxicity of quinolones

Reactions of the gastrointestinal tract, the CNS and the skin are the most often observed adverse effects during therapy with fluoroquinolones. At least for some of the newer fluoroquinolones a steep dose-response relationship of adverse effects seems to exist. Pathogenesis of the neurotoxic effects of fluoroquinolones is still unknown. Among the newer drugs, trovafloxacin caused mild CNS reactions such as dizziness and lightheadedness in a considerable proportion of patients. Young females seem to be especially sensitive to this effect, which diminishes during treatment or if taken together with food. Cardiotoxic potentials of sparfloxacin and grepafloxacin are higher than those of other fluoroquinolones, but during therapy no clearcut drug-related serious reactions have been reported, apart from a slight prolongation of the QT interval. However, to avoid risks these drugs should not be prescribed to patients with known prolongation of the QT interval (e.g. patients on antiarrhythmics). Phototoxicity has been described for all quinolones, but derivatives with a halogen atom at position 8 show the highest potential for such reactions. Fleroxacin, sparfloxacin, clinafloxacin and lomefloxacin belong to this group of fluoroquinolones. The phototoxic potential of the other new fluoroquinolones is considerably lower, but extensive exposure to UV light should generally be avoided during therapy with all quinolones. Chondrotoxicity of quinolones, as observed in immature animals, can affect articular cartilage and/or the epiphyseal growth plate, depending on the developmental stage. Pathogenesis of chondrotoxicity can probably be explained by the magnesium-chelating properties of these drugs. As juveniles are especially sensitive, use of these drugs in paediatrics should be restricted to carefully selected indications (such as the use of ciprofloxacin in cystic fibrosis). Another manifestation of the toxic effects of quinolones on connective tissue structures are tendopathies. Tendinitis and tendon ruptures have occurred as late as several months after quinolone treatment. Overall, quinolones are well tolerated drugs. Their specific toxic potentials have to be considered when they are chosen for treatment of bacterial infections.