A comprehensive model for enrofloxacin to ciprofloxacin transformation and disposition in dog

Development of a new antibiotic-induced dysbiosis model of the canine colonic microbiota

As in humans, antibiotics are widely used in dogs to treat gastrointestinal infections, contributing to the global burden of antimicrobial resistance on both human and animal health. Close contact between pets and their owners can lead to horizontal transfer of gut microbes, including transmission of antibiotic resistance. Nevertheless, until now, the impact of antibiotics on the canine gut microbiota has been poorly described. The aim of this study was to adapt the canine mucosal artificial colon (CANIM-ARCOL) model, reproducing the main nutritional, physicochemical and microbial parameters found in the large intestine of the dog to simulate an antibiotic-induced perturbation. Following initial investigation of five antibiotic cocktails at in-field doses, a 5-day regimen of metronidazole/enrofloxacin (ME) was selected for further model development. Two CANIM-ARCOL bioreactors were inoculated with a faecal sample (n=2 donors) and run in parallel for 26 days under control or antibiotic conditions. ME reduced microbial diversity and induced major shifts in bacterial populations, leading to a state of dysbiosis characterized by an increase in the relative abundance of Streptococcaceae, Lactobacillaceae and Enterobacteriaceae, and a decrease in the relative abundance of Bacteroidaceae, Fusobacteriota and Clostridiaceae. Overall, mucus-associated microbiota were less impacted by antibiotics than luminal microbes. Microbial alterations were associated with drastic decreases in gas production and short-chain fatty acid concentrations. Finally, the model was well validated through in-vitro-in-vivo comparisons in a study in dogs. The CANIM-ARCOL model provides a relevant platform as an alternative to in-vivo assays for an in-depth understanding of antibiotic-microbiota interactions and further testing of restoration strategies at individual level.

Intramuscular therapeutic doses of enrofloxacin affect microbial community structure but not the relative abundance of fluoroquinolones resistance genes in swine manure

Livestock manure is a major source of veterinary antibiotics and antibiotic resistance genes (ARGs). Elucidation of the residual characteristics of ARGs in livestock manure following the administration of veterinary antibiotics is critical to assess their ecotoxicological effects and environmental contamination risks. Here, we investigated the effects of enrofloxacin (ENR), a fluoroquinolone antibiotic commonly used as a therapeutic drug in animal husbandry, on the characteristics of ARGs, mobile genetic elements, and microbial community structure in swine manure following its intramuscular administration for 3 days and a withdrawal period of 10 days. The results revealed the highest concentrations of ENR and ciprofloxacin (CIP) in swine manure at the end of the administration period, ENR concentrations in swine manure in groups L and H were 88.67 ± 45.46 and 219.75 ± 88.05 mg/kg DM, respectively. Approximately 15 fluoroquinolone resistance genes (FRGs) and 48 fluoroquinolone-related multidrug resistance genes (F-MRGs) were detected in swine manure; the relative abundance of the F-MRGs was considerably higher than that of the FRGs. On day 3, the relative abundance of qacA was significantly higher in group H than in group CK, and no significant differences in the relative abundance of other FRGs, F-MRGs, or MGEs were observed between the three groups on day 3 and day 13. The microbial community structure in swine manure was significantly altered on day 3, and the altered community structure was restored on day 13. The FRGs and F-MRGs with the highest relative abundance were qacA and adeF, respectively, and Clostridium and Lactobacillus were the dominant bacterial genera carrying these genes in swine manure. In summary, a single treatment of intramuscular ENR transiently increased antibiotic concentrations and altered the microbial community structure in swine manure; however, this treatment did not significantly affect the abundance of FRGs and F-MRGs.

Pharmacokinetics in Penguins Compared to Other Avian Species: A Review of Enrofloxacin and Voriconazole

Australasia is home to unique and endangered avian species. Drug administration to this group of animal patients for prophylaxis and treatment is challenging from a number of different perspectives. A key limitation for optimal drug dosing in birds is the lack of published pharmacokinetic studies to guide dose requirements. The aim of this review was to systematically investigate published literature on pharmacokinetics in penguin species and compare that with the pharmacokinetics of other avian species with a focus on two drugs: enrofloxacin and voriconazole. The review was conducted following PRISMA guidelines. A systematic literature search was performed in Pubmed, Embase, Scopus, and Web of Science databases. A key finding is that penguin pharmacokinetics differs from other avian species, with weight-adjusted AUC and Cmax values higher than most other avian species (e.g., for enrofloxacin, the AUC in the African penguin is 85.7 μg h/mL, which is more than double the other bird species). Doses for some avian species may be successfully extrapolated from other avian species; however, it appears important to consider factors other than just body weight (e.g., clearance mechanism and drug physicochemical characteristics). Consequently, there is an important need for robust pharmacokinetic data in wildlife species to ensure optimal therapy for this special group of patients. As part of this review, we identify key aspects that should be considered when estimating dose in species for which there is limited pharmacokinetic information available.

Quantifying community-wide antibiotic usage via urban water fingerprinting: Focus on contrasting resource settings in South Africa

There has been a significant increase in antimicrobial agents (AAs) usage, globally - however the relative consumption is unevenly distributed between nations. Inappropriate use of antibiotics can harbour inherent antimicrobial resistance (AMR); therefore, it is important to understand and monitor community-wide prescribing and consumption behaviours throughout different communities around the world. Wastewater-Based Epidemiology (WBE) is a novel tool enabling low cost and large scale studies focussed on AA usage patterns. The back-calculation of community antimicrobial intake was performed from quantities measured in municipal wastewater and informal settlement discharge in the city of Stellenbosch, utilising WBE. Seventeen antimicrobials, and their human metabolites, were evaluated, in concordance with prescription records corresponding to the catchment region. The proportional excretion, biological/chemical stability, and method recovery of each analyte were all crucial factors in the efficacy of the calculation. Mass per day measurements were normalised to the catchment area via population estimates. Municipal wastewater treatment plant population estimates were used to normalise the wastewater samples and prescription data (mg/day/1000 inhabitants). Population estimates for the informal settlements were less accurate due to a lack of reliable sources that were relevant to the sampling time period. Both mass loads and normalised loads suggested higher than average usage throughout the settlements, relative to municipal wastewater. This was seen most prominently in emtricitabine and lamivudine; but also, sulfamethoxazole, trimethoprim, sulfadiazine, clindamycin, ciprofloxacin, ofloxacin, and doxycycline. Urban water fingerprinting (UWF) data triangulation with prescription datasets showed good correlations for several antimicrobial agents (AAs) (e.g., clindamycin, clarithromycin, ofloxacin, and doxycycline). It also revealed discrepancies in usage for some compounds (e.g., tetracycline and sulfapyridine). This might be linked with a lack of pharma compliance in prescription datasets; erroneous association of prescription boundaries with the sewerage catchment; and/or uncertainties within the sewerage catchment (e.g., population estimations). The UWF tool provided a comprehensive overview of multiclass AAs usage, both prescription and over-the counter. For example, tetracycline was not reported in available prescription statistics, but was detected at an average of 18.4 mg/day/1000inh; and no antiviral prescriptions were obtained, but emtricitabine and lamivudine were quantified at 2415.4 and 144.4 mg/day/1000inh, respectively. A lack of clarity regarding prescriptions and a lack of inclusion of several critical (often over-the-counter) medications in public health databases makes WBE a useful and comprehensive epidemiology tool for tracking pharma usage within a catchment.

Inhibition of Staphylococcus pseudintermedius Efflux Pumps by Using Staphylococcus aureus NorA Efflux Pump Inhibitors

One promising approach in treating antibiotic-resistant bacteria is to "break" resistances connected with antibacterial efflux by co-administering efflux pump inhibitors (EPIs) with antibiotics. Here, ten compounds, previously optimized to restore the susceptibility to ciprofloxacin (CIP) of norA-overexpressing Staphylococcus aureus, were evaluated for their ability to inhibit norA-mediated efflux in Staphylococcus pseudintermedius and synergize with CIP, ethidium bromide (EtBr), gentamycin (GEN), and chlorhexidine digluconate (CHX). We focused efforts on S. pseudintermedius as a pathogenic bacterium of concern within veterinary and human medicine. By combining data from checkerboard assays and EtBr efflux inhibition experiments, the hits 2-arylquinoline 1, dihydropyridine 6, and 2-phenyl-4-carboxy-quinoline 8 were considered the best EPIs for S. pseudintermedius. Overall, most of the compounds, except for 2-arylquinoline compound 2, were able to fully restore the susceptibility of S. pseudintermedius to CIP and synergize with GEN as well, while the synergistic effect with CHX was less significant and often did not show a dose-dependent effect. These are valuable data for medicinal chemistry optimization of EPIs for S. pseudintermedius and lay the foundation for further studies on successful EPIs to treat staphylococcal infections.

Drug efflux transporters in Staphylococcus pseudintermedius: in silico prediction and characterization of resistance

OBJECTIVES

To perform an in silico prediction of drug efflux pumps (EPs) in Staphylococcus pseudintermedius and investigate their role in conferring resistance to antibiotic and biocidal agents and biofilm formation.

METHODS

A S. pseudintermedius efflux mutant was obtained by stimulating an isogenic line (ATCC 49444) with increasing concentrations of an efflux system substrate. Changes in antimicrobial susceptibility and biofilm-forming capability were evaluated in the presence/absence of the EP inhibitors (EPIs) thioridazine and reserpine and the efflux activity was assayed by fluorometry. Homologues of EPs of Staphylococcus aureus and Staphylococcus epidermidis were searched by exploratory GenBank investigations. Gene expression analyses and sequencing were then conducted on selected genes.

RESULTS

Susceptibility to chlorhexidine, gentamicin and ciprofloxacin, but not enrofloxacin, was affected by the increased efflux and it was variably restored by the EPIs. The efflux mutant showed much greater biofilm formation that the original strain, which was significantly inhibited by thioridazine and reserpine at MIC/2. A high expression of norA, which was mgrA-independent, was found in the S. pseudintermedius efflux mutant, apparently regulated by an 11 bp deletion in its promoter region, whilst lmrB was transitorily overexpressed. icaA, which encodes the polysaccharide intercellular adhesin forming the extracellular matrix of staphylococcal biofilm, was also up-regulated.

CONCLUSIONS

EPs, particularly NorA, are supposed to have complex involvement in multiple stages of resistance development. Overexpression of EPs appears to be correlated with a remarkable increase of S. pseudintermedius biofilm production; however, the regulatory mechanisms remain to be explored.

A highly sensitive impedimetric sensor based on a MIP biomimetic for the detection of enrofloxacin

The benefits of molecularly imprinted polymer (MIP) technology in creating artificial receptors to replace natural counterparts have piqued the interest of numerous researchers in recent years. We propose a biomimetic enrofloxacin-MIP for enrofloxacin (ENRO) antigen detection using gold nanoparticles (AuNPs) and MIP methodologies in this study. A self-assembled monomer layer of aminothiophenol was used to immobilize a pre-formed complex of the anti-enrofloxacin monoclonal antibody and enrofloxacin antigen onto the surface of an AuNP coated screen-printed carbon ink electrode (SPCE). The poly-(aminothiophenol) layer thickness was adjusted to entrap and restrict enrofloxacin antigens near the surface. The imprinting and removal of the enrofloxacin antigen in the MIP film were strongly validated by the Raman spectra. The final mAb-MIP sensor had better sensitivity (302 Ω mL ng^-1) and a better detection limit (0.05 ng mL^-1) than self-assembled monolayer (SAM)-based immunosensors, which had 102 Ω mL ng^-1 and 0.1 ng mL^-1, respectively.

Bacteria isolated from hospital, municipal and slaughterhouse wastewaters show characteristic, different resistance profiles

Multidrug-resistant bacteria cause difficult-to-treat infections and pose a risk for modern medicine. Sources of multidrug-resistant bacteria include hospital, municipal and slaughterhouse wastewaters. In this study, bacteria with resistance to 3rd generation cephalosporins were isolated from all three wastewater biotopes, including a maximum care hospital, municipal wastewaters collected separately from a city and small rural towns and the wastewaters of two pig and two poultry slaughterhouses. The resistance profiles of all isolates against clinically relevant antibiotics (including β-lactams like carbapenems, the quinolone ciprofloxacin, colistin, and trimethoprim/sulfamethoxazole) were determined at the same laboratory. The bacteria were classified according to their risk to human health using clinical criteria, with an emphasis on producers of carbapenemases, since carbapenems are prescribed for hospitalized patients with infections with multi-drug resistant bacteria. The results showed that bacteria that pose the highest risk, i. e., bacteria resistant to all β-lactams including carbapenems and ciprofloxacin, were mainly disseminated by hospitals and were present only in low amounts in municipal wastewater. The isolates from hospital wastewater also showed the highest rates of resistance against antibiotics used for treatment of carbapenemase producers and some isolates were susceptible to only one antibiotic substance. In accordance with these results, qPCR of resistance genes showed that 90% of the daily load of carbapenemase genes entering the municipal wastewater treatment plant was supplied by the clinically influenced wastewater, which constituted approximately 6% of the wastewater at this sampling point. Likewise, the signature of the clinical wastewater was still visible in the resistance profiles of the bacteria isolated at the entry into the wastewater treatment plant. Carbapenemase producers were not detected in slaughterhouse wastewater, but strains harboring the colistin resistance gene mcr-1 could be isolated. Resistances against orally available antibiotics like ciprofloxacin and trimethoprim/sulfamethoxazole were widespread in strains from all three wastewaters.

Comparative bioavailability of enrofloxacin in dogs when concealed in noncommercial morsels, either as tablet or as enrofloxacin-alginate dried beads

Administration of enrofloxacin tablets concealed in improvised morsels to elude the unpleasant flavor of this drug is likely to diminish maximum plasma concentrations (C_max ) reached by this drug, jeopardizing treatment efficacy. To avoid this, the hypothesis that alginate dried beads containing enrofloxacin (ADBE) could modify the pharmacokinetics of enrofloxacin in dogs was tested. ADBE were manufactured and pharmaceutically defined as having high entrapment efficiency (>90%) and a drug loading capacity of 56%-67%. Based on the hydrophilic nature of alginate and its interaction with the anionic charge of the amino groups of enrofloxacin, a novel modified release system was obtained in which ADBE give place to both a rapid diffusion releasing of enrofloxacin and a maintained release. The ADBE concealed in a sausage (ADBEs) achieved both the highest Cmax (5.1 µg/ml ± 0.3 SD) and the area under the concentration versus time (AUC_0-24 ) (41.2 µg hr^-1  ml^-1  ± 6.9 SD). The tablet administered alone had a C_max of 1.9 µg/ml ± 0.3 SD and an AUC_0-24  = 16.5 µg h^-1  ml^-1  ± 3.5 SD, while the tablet concealed in a sausage reached a C_max of 1.2 µg/ml ± 0.3 SD with an AUC_0-24  = 12.3 µg hr^-1  ml^-1  ± 3.8 SD (p < .05 in both cases when confronting ADBEs vs. tablets). Consequently, C_max /MIC and AUC_0-24 /MIC ratios are higher for ADBEs. Other PK parameters were statistically indistinguishable, and other morsels containing enrofloxacin as a tablet or as ADBE rendered less favorable PK parameters. Due to ease of administration and favorable PK for ADBE concealed in a sausage, this pharmaceutical design can be regarded as PK/PD consistent and worthy of clinical studies.

Therapeutic administration of enrofloxacin in mice does not select for fluoroquinolone resistance inCampylobacter jejuni

Enrofloxacin is registered for therapeutic use in beef cattle to treat bovine respiratory disease in Canada. A murine model was used to experimentally examine the impact of therapeutic administration of enrofloxacin on fluoroquinolone resistance development in Campylobacter jejuni. Administration of enrofloxacin to mice via subcutaneous injection or per os routes resulted in equivalent levels of bioactive enrofloxacin within the intestine, but bioactivity was short-lived (<48 h after cessation). Enrofloxacin administration did not affect densities of total bacteria, Firmicutes, or Bacteroidetes in digesta and had modest impacts on densities of Enterobacteriaceae. All mice inoculated with C. jejuni NCTC 11168 became persistently colonized by the bacterium. Enrofloxacin reduced C. jejuni cell densities within the cecal and colonic digesta for all treatments, and densities shed in feces as a function of antibiotic duration. None of the C. jejuni isolates recovered from mice after administration of enrofloxacin (n = 260) developed resistance to ciprofloxacin regardless of method or duration of administration. Furthermore, only modest shifts in the minimum inhibitory concentration of the isolates by treatment were noted. The study findings indicate that the risk posed by short-term subcutaneous administration of enrofloxacin for the development of fluoroquinolone resistance in mammals is low.

Effect of Sucralfate on the Relative Bioavailability of Enrofloxacin and Ciprofloxacin in Healthy Fed Dogs

Background

Sucralfate impairs absorption of ciprofloxacin and other fluoroquinolones in humans, but no sucralfate–fluoroquinolone interaction has been reported in dogs. Veterinary formularies recommend avoiding concurrent administration of these medications, which might impact compliance, therapeutic success, and resistance selection from fluoroquinolones.

Objectives

To determine whether a drug interaction exists when sucralfate is administered to fed dogs concurrently with ciprofloxacin or enrofloxacin, and whether a 2 hour delay between fluoroquinolone and sucralfate affects fluoroquinolone absorption.

Animals

Five healthy Greyhounds housed in a research colony.

Methods

This was a randomized crossover study. Treatments included oral ciprofloxacin (C) or oral enrofloxacin (E) alone, each fluoroquinolone concurrently with an oral suspension of sucralfate (CS, ES), and sucralfate suspension 2 hours after each fluoroquinolone (C2S, E2S). Fluoroquinolone concentrations were evaluated using liquid chromatography with mass spectrometry.

Results

Drug exposure of ciprofloxacin was highly variable (AUC 5.52–22.47 h μg/mL) compared to enrofloxacin (AUC 3.86–7.50 h μg/mL). The mean relative bioavailability for ciprofloxacin and concurrent sucralfate was 48% (range 8–143%) compared to ciprofloxacin alone. Relative bioavailability of ciprofloxacin improved to 87% (range 37–333%) when sucralfate was delayed by 2 hours. By contrast, relative bioavailability for enrofloxacin and concurrent sucralfate was 104% (94–115%).

Conclusions and Clinical Importance

A possible clinically relevant drug interaction for the relative bioavailability of ciprofloxacin with sucralfate was found. No significant difference in bioavailability was documented for enrofloxacin with sucralfate. Further research is warranted in fasted dogs and clinical cases requiring enrofloxacin or other approved fluoroquinolones in combination with sucralfate.

In vitro activity of chloramphenicol, florfenicol and enrofloxacin against Chlamydia pecorum isolated from koalas (Phascolarctos cinereus)

OBJECTIVE

To determine the in vitro susceptibilities of koala isolates of Chlamydia pecorum to enrofloxacin and chloramphenicol, which are frequently used to treat koalas with chlamydiosis, and florfenicol, a derivative of chloramphenicol.

METHODS

The in vitro susceptibilities were determined by culturing three stored isolates and seven clinical swabs of C. pecorum. Susceptibility testing was undertaken using cycloheximide-treated buffalo green monkey kidney cells in 96 well microtitre plates.

RESULTS

The minimum inhibitory concentrations (MICs) for all isolates were 0.25-0.50 µg/mL (enrofloxacin), 1-2 µg/mL (chloramphenicol), and 1-2 µg/mL (florfenicol). Minimum bactericidal concentration (MBC) values for five isolates were also determined and were within one two-fold dilution of MICs. The MICs and MBCs of these antimicrobials were within ranges previously reported for other chlamydial species.

CONCLUSION

When combined with previously published pharmacokinetic data, the in vitro susceptibility results support chloramphenicol as a more appropriate treatment option than enrofloxacin for koalas with chlamydiosis. The susceptibility results also indicate florfenicol may be an appropriate treatment option for koalas with chlamydiosis, warranting further investigation.

Development of sensitive and reliable LC-MS/MS methods for the determination of three fluoroquinolones in water and fish tissue samples and preliminary environmental risk assessment of their presence in two rivers in northern Poland

Antibiotic consumption (e.g. fluoroquinolones (FQs)) and, as a consequence, their presence in the environment, have received a lot of attention in the last several years due to increasing numbers of diseases and infections that are becoming resistant to traditional treatments for both humans and animals. In addition, even though antibiotics are safe for human and veterinary usage, ecosystems may be exposed to these substances. In this study, analytical methods for determining enrofloxacin (ENR), norfloxacin (NOR) and ciprofloxacin (CIP) in water samples and fish tissue based on the LC-MS/MS technique were developed and validated. As there is no data available concerning the risks posed by antibiotics in Poland, the proposed methods were applied for monitoring drug presence in environmental samples collected from two rivers in northern Poland. Evaluations of the ecotoxicity of ENR, NOR and CIP towards four different species of aquatic organisms: marine bacteria (Vibrio fischeri), green algae (Scenedesmus vacuolatus), duckweed (Lemna minor) and crustacean (Daphnia magna), were also carried out. All the investigated compounds were detected at least once in the survey. NOR was found to be the most ubiquitous drug with concentrations of up to 442.8 ng L(-1). Moreover, it was established that L. minor is the most sensitive species to the investigated drugs (EC50NOR = 0.13 mg L(-1), EC50ENR = 0.22 mg L(-1) and EC50CIP = 0.34 mg L(-1)). The calculated risk quotient (RQ) values confirmed that the concentrations of the investigated FQs in the environmental samples were at a level of moderate environmental risk (1<RO ≤ 10), however, for CIP they were found to be closer to a level of high environmental risk (RQCIP = 8.1).

Evaluation of enrofloxacin use in koalas (Phascolarctos cinereus) via population pharmacokinetics and Monte Carlo simulation

Clinically normal koalas (n = 6) received a single dose of intravenous enrofloxacin (10 mg/kg). Serial plasma samples were collected over 24 h, and enrofloxacin concentrations were determined via high-performance liquid chromatography. Population pharmacokinetic modeling was performed in S-ADAPT. The probability of target attainment (PTA) was predicted via Monte Carlo simulations (MCS) using relevant target values (30-300) based on the unbound area under the curve over 24 h divided by the minimum inhibitory concentration (MIC) (fAUC0-24 /MIC), and published subcutaneous data were incorporated (Griffith et al., 2010). A two-compartment disposition model with allometrically scaled clearances (exponent: 0.75) and volumes of distribution (exponent: 1.0) adequately described the disposition of enrofloxacin. For 5.4 kg koalas (average weight), point estimates for total clearance (SE%) were 2.58 L/h (15%), central volume of distribution 0.249 L (14%), and peripheral volume 2.77 L (20%). MCS using a target fAUC0-24 /MIC of 40 predicted highest treatable MICs of 0.0625 mg/L for intravenous dosing and 0.0313 mg/L for subcutaneous dosing of 10 mg/kg enrofloxacin every 24 h. Thus, the frequently used dosage of 10 mg/kg enrofloxacin every 24 h subcutaneously may be appropriate against gram-positive bacteria with MICs ≤ 0.03 mg/L (PTA > 90%), but appears inadequate against gram-negative bacteria and Chlamydiae in koalas.

The effect of 'allergenic' and 'nonallergenic' antibiotics on dog keratinocyte viability in vitro

BACKGROUND

Immune-mediated adverse drug reactions (drug hypersensitivity) are relatively common in veterinary medicine, but their pathogenesis is not well understood. For an unknown reason, delayed drug hypersensitivity often targets the skin. Antibiotics, especially β-lactams and sulfonamides, are commonly associated with these adverse events. The 'danger theory' hypothesizes that 'danger' signals, such as drug-induced cell death, might be part of the pathogenesis of drug hypersensitivity reactions.

HYPOTHESIS/OBJECTIVES

The goal of this study was to determine whether antibiotics that are commonly associated with cutaneous drug hypersensitivity (allergenic) decrease canine keratinocyte viability in vitro more than antibiotics that rarely cause such reactions (nonallergenic).

METHODS

Immortalized canine keratinocytes (CPEK cells) were exposed to a therapeutic range of drug concentrations of four 'allergenic' antibiotics (two β-lactams, i.e. amoxicillin and cefalexin, and two sulfonamides, i.e. sulfamethoxazole and sulfadimethoxine) or two 'nonallergenic' antibiotics (enrofloxacin and amikacin) over 48 h (2, 4, 8, 24 and 48 h). The reactive nitroso metabolite of sulfamethoxazole was also tested.

RESULTS

Cefalexin (2 mmol/L) significantly decreased cell viability after 48 h (28 ± 7%; P = 0.035). The nitroso metabolite of sulfamethoxazole (100 μmol/L) decreased cell viability after 2 h (21 ± 7%; P = 0.049), but cell numbers were increased after 8 h (22 ± 6%; P = 0.018). In addition, enrofloxacin (500 μmol/L) also significantly decreased cell viability by 37% (±6%; P = 0.0035) at 24 h and by 70% (±8%; P < 0.001) at 48 h.

CONCLUSION

It appears that the effect of drugs on the in vitro viability of dog keratinocytes is not a good predictor of the 'allergenic' potential of an antibiotic. Further work is required to investigate other drug-induced 'danger' signals in dog keratinocytes exposed to 'allergenic' antibiotics in vitro.

Detection of antibacterial-like activity on a silica surface: fluoroquinolones and their environmental metabolites

BACKGROUND, SCOPE, AND AIMS: Antibacterial fluoroquinolones (FQs) are third-generation antibiotics that are commonly used as therapeutic treatments of respiratory and urinary tract infections. They are used far less in intensively farmed animal production systems, though their use may be permitted in the veterinary treatments of flocks or in medicated feeds. When used, only a fraction of ingested parent FQ actually reaches the in vivo target site of infection, while the remainder is excreted as the parent FQ and its metabolized products. In many species' metabolism, enrofloxacin (EF) is converted into ciprofloxacin (CF) while both FQs are classified as parent FQs in human treatments. It is therefore likely that both FQs and their metabolic products will contribute to a common pool of metabolites in biological wastes. Wastes from intensive farming practices are either directly applied to agricultural land without treatment or may be temporarily stored prior to disposal. However, human waste is treated in sewage treatment plants (STPs) where it is converted into biosolids. In the storage or treatment process of STPs, FQs and their in vivo metabolites are further converted into other environmental metabolites (FQEMs) by ex vivo physicochemical processes that act and interact to produce complex mixtures of FQEMs, some of which have antibacterial-like activities. Biosolids are then often applied to agricultural land as a fertilizer amendment where FQs and FQEMs can be further converted into additional FQEMs by soil processes. It is therefore likely that FQ-contaminated biowaste-treated soils will contain complex mixtures of FQEMs, some of which may have antibacterial-like activities that may be expressed on bacteria endemic to the receiving agricultural soil environment. Concern has arisen in the scientific and in the general community that repeated use of FQ-contaminated biowaste as fertilizer amendments of nutrient-impoverished agricultural land may create a selective environment in which FQ-resistant bacteria might grow. The likelihood of this happening will depend, to some extent, on whether bioactive FQEMs are first synthesized from the parent FQs by the action and interaction of in vivo and ex vivo processes producing bioactive FQEMs in biowastes and biosolids. The postulated creation of a selective environment will also depend, in part, on whether such bioactive FQEMs are biologically available to bacteria, which may, in turn, be influenced by soil type, amendment regime, and the persistence of the bioactive FQEMs. Additionally, soil bacteria and soil processes may be affected in different ways or extents by bioactive FQEMs that could possibly act additively or synergistically at ecological targets in these non-target bacteria. This is an important consideration, since, while parent FQs have well-defined ecological targets (DNA gyrase and topoisomerase IV) and modes of bactericidal action, the FQEMs and their possible modes of action on the many different species of soil bacteria is less well studied. It is therefore understandable that there is a lack of conclusive evidence directly attributing biosolid usage to any increase in FQ-resistant bacteria detected in biowaste-amended agricultural soil. However, a lack of evidence may simply imply that a causal relationship between biosolid usage programs and any detection of low levels of FQ-resistant bacteria in soils has yet to be established, rather than an assumption of no relationship whatsoever. Based on results presented in this paper, the precautionary principle should be applied in the usage of FQ-contaminated biosolids as fertilizer amendments of agricultural land. The aim of this research was to test whether any bioactive FQEMs of EF could be synthesized by aerobic fermentation processes using Mycobacterium gilvum (American Tissue Culture Collection) and a mixed culture of microorganisms derived from an agricultural soil. High-performance thin-layer chromatography (HPTLC) and bioautography were tested as screening techniques in the detection and analysis of bioactive FQEMs.

MATERIALS AND METHODS

FQEMs derived from M. gilvum and mixed (soil) culture aerobic ferments were fractionated using preparative HPTLC. A standard strain of Escherichia coli was then used as the reporter organism in a bioautography assay in the detection of bioactive-FQEMs on a mid-section of the HPTLC plate. Plate sections were reassembled, and a photograph was taken under low-intensity ultraviolet (UV) light to reveal regions that contained analytes that had UV chromophores and antibacterial-like activities.

RESULTS AND DISCUSSION

Many fractionated FQEMs displayed antibacterial-like activity while bound to silica gel HPTLC plates. These results also provide evidence that sufficient quantities of biologically active FQEMs were biologically available from a silica gel surface to prevent the adherent growth of E. coli. Six to seven FQEMs derived from EF using aerobic fermentation processes had antibacterial-like activities, while two FQEMs were also detectable using UV light. Furthermore, similar banding patterns of antibacterial-like activity were observed in both the monoculture (M. gilvum) and mixed culture bioautography assays, indicating that similar processes operated in both aerobic fermentations, either producing similar biologically active FQEMs or biologically active FQEMs that had similar physicochemical properties in both ferments. The simplest explanation for these findings is that the tested agricultural soil also contained mycobacteria that metabolized EF in a similar way to the purchased standard monoculture M. gilvum. Additionally, the marked contrast between the bioautography results and the UV results indicated that the presence of UV chromophores is not a prerequisite for the detection of antibacterial-like activity.

CONCLUSIONS

A reliance on spectrophotometric techniques in the detection of bioactive FQEMs in the environment may underestimate component antibacterial-like activity and, possibly, total antibacterial-like activity expressed by EF and its FQEMs. The described bioautography method provides a screening technique with which antibacterial-like activities derived from EF and possibly other FQs can be detected directly on silica gel HPTLC plates.

RECOMMENDATIONS

It is recommended that both bioassay and instrumental analytical techniques be used in any measurement of hazard and risk relating to antibacterial-like activities in the environment that are derived from fluoroquinolone antibiotics and their environmental metabolites.

Environmental metabolites of fluoroquinolones: synthesis, fractionation and toxicological assessment of some biologically active metabolites of ciprofloxacin

BACKGROUND, AIM, AND SCOPE

Biowastes produced by humans and animals are routinely disposed of on land, and concern is now growing that such practices provide a pathway for fluoroquinolone (FQs) antibacterial agents and their environmental metabolites (FQEMs) to contaminate the terrestrial environment. The focus of concern is that FQs and FQEMs may accumulate in amended soils to then adversely impact on the terrestrial environment. One postulated impact is the development of a selective environment in which FQ-resistant bacteria may grow. To find evidence in support of an accumulation of antibacterial-like activity, it was first necessary to establish whether any biologically active FQEMs could be synthesized by physicochemical factors that are normally present in the environment. However, many FQEMs are not commercially available to be used as standards in such studies. FQEMs were therefore synthesized using well-defined processes. They were subsequently analyzed using spectroscopy (UV-vis) and high performance liquid chromatography with mass spectral detection. The antibacterial-like activities of fractionated FQEMs were then assessed in novel bacterial growth inhibition bioassays, and results were compared to those obtained from instrumental analyses.

MATERIALS AND METHODS

Parent FQs were either exposed to sunlight or were synthesized using defined aerobic microbial (Mycobacterium gilvum or a mixed culture derived from an agricultural soil) fermentation processes. Mixtures of FQEMs derived from photo- and (intracellular) microbial processes were isolated by preparative chromatography and centrifugation techniques, respectively. Mixtures were subsequently fractionated using analytical high-performance thin layer chromatography (HPTLC), and excised analytes were tested in bioautography assays for their antibacterial-like activities. Two bacteria, Escherichia coli (E. coli) and Azospirillum brasilense (A. brasilense) were used as reporter organisms in testing FQ standards and any subtle differences between biologically active FQEMs of ciprofloxacin (CF).

RESULTS AND DISCUSSION

FQEMs produced in the photo-synthetic process had UV-vis profiles that were indistinguishable from the parent FQs, and yet mass spectral data revealed the presence of N-formylciprofloxacin (FCF). In contrast, the UV-vis profiles of FQEMs synthesized by M. gilvum and a mixed culture of microorganisms had UV-vis profiles that were similar to one another and markedly different to the parent fluoroquinolones. Mass spectral studies confirmed the presence of FCF and N-acetylciprofloxacin in both microbial ferments. In addition, a photo-FQEM (Cp 6), three M. gilvum FQEMs (Cm 5, Cm 8, and Cm 10) and a mixed culture FQEM (Cs 6) of CF and many other FQEMs of CF, norfloxacin (NF), and enrofloxacin (EF) were fractionated using HPTLC, although their identities have yet to be confirmed. Differences between bioautography results were obtained when E. coli or A. brasilense were used as reporter organisms. Parent FQs (CF and EF) and the FQEMs of CF (Cp 6, Cm 8, and Cs 6) displayed antibacterial-like activity when using E. coli as the reporter organism. In contrast, A. brasilense was insensitive to parent CF and sensitive to EF and all tested FQEMs of CF. Results are consistent with photo- and microbial processes modifying CF in different ways, with the latter changing the UV-vis chromophores. It can be inferred that a lack of detection of analytes (especially photo-FQEMs) when using UV-vis does not necessarily indicate an absence of analyte. Additionally, similarities between the UV-vis profiles of FQEMs extracted from the (monoculture) M. gilvum and the mixed culture microbial aerobic ferments are consistent with similar processes operating in both ferments. Results of HPTLC and bioautography studies revealed that mixtures of (photo- and microbial) FQEMs could be fractionated into individual components.

CONCLUSIONS

Bioactive FQEMs of ciprofloxacin, as a representative FQ, can be synthesized by photo- and microbial processes, and their detection required the use of both instrumental and bioautography analytical techniques. It is likely that such FQEMs will also be present on agricultural land that has been repeatedly amended with FQ-contaminated biosolids.

RECOMMENDATIONS AND PERSPECTIVES

The use of instrumental analytical techniques alone and especially photometric detection techniques will underestimate antibacterial-like activities of FQEMs. Moreover, the extraction technique(s) and the selected toxicological endpoint(s) require careful consideration when assessing bioactivity. It is therefore recommended that instrumental analytical techniques and several bioautography assays be performed concurrently, and bioautography assays should use a variety of reporter organisms. Two types of bacterial growth bioassays are recommended in any assessment of antibacterial-like activity derived from CF (and possibly from other FQs). A standardized E. coli bioassay should be used as a general screening procedure to facilitate intra- and inter-laboratory exchange of data. Additionally, soil-specific (region-specific) growth inhibition bioassays should be undertaken using several species of endemic soil bacteria. It is likely that the two sets of data will be useful in future risk assessment processes.

Population pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin in chicken based on retrospective data, incorporating first-pass metabolism

A population pharmacokinetic (PPK) model for enrofloxacin and its metabolite ciprofloxacin in chicken based on retrospective data was developed. Plasma concentrations of enrofloxacin and its metabolite ciprofloxacin were determined in blood samples from chicken administered either enrofloxacin via oral and intravenous routes or ciprofloxacin via intravenous injection. The disposition of enrofloxacin and ciprofloxacin was described simultaneously by an integrated mathematic model. Two compartments were used to describe the enrofloxacin and ciprofloxacin disposition profiles. The formation of ciprofloxacin was through the central compartment of enrofloxacin. The integrated model was estimated with nonlinear mixed effects model (NONMEM). The total clearance of enrofloxacin (CLEN) and ciprofloxacin (CLCP) was 0.613 L/h and 1.15 L/h, respectively. Correlation between CLEN, the central compartment volume of distribution for enrofloxacin (V2) and CLCP was estimated. After intravenous administration of enrofloxacin, the transformation rate of enrofloxacin to ciprofloxacin was 0.429 L/h. The bioavailability factor after oral administration was 0.926, and 12.6% of enrofloxacin after oral administration was transformed to ciprofloxacin via first-pass effect. Pharmacodynamic (PD) evaluation was performed using area under concentration time curve of active moiety from 0 to 24 h and MIC collected from literature. This study is the first one to use PPK method to investigate parent drug and its metabolite disposition and PDs using an integrated model in veterinary medicine.

Plasma and interstitial fluid pharmacokinetics of enrofloxacin, its metabolite ciprofloxacin, and marbofloxacin after oral administration and a constant rate intravenous infusion in dogs

Enrofloxacin and marbofloxacin were administered to six healthy dogs in separate crossover experiments as a single oral dose (5 mg/kg) and as a constant rate IV infusion (1.24 and 0.12 mg/h.kg, respectively) following a loading dose (4.47 and 2 mg/kg, respectively) to achieve a steady-state concentration of approximately 1 microg/mL for 8 h. Interstitial fluid (ISF) was collected with an in vivo ultrafiltration device at the same time period as plasma to measure protein unbound drug concentrations at the tissue site and assess the dynamics of drug distribution. Plasma and ISF were analyzed for enrofloxacin, its active metabolite ciprofloxacin, and for marbofloxacin by high performance liquid chromatography (HPLC). Lipophilicity and protein binding of enrofloxacin were higher than for marbofloxacin and ciprofloxacin. Compared to enrofloxacin, marbofloxacin had a longer half-life, higher Cmax, and larger AUC(0-infinity) in plasma and ISF after oral administration. Establishing steady state allowed an assessment of the dynamics of drug concentrations between plasma and ISF. The ISF and plasma-unbound concentrations were similar during the steady-state period despite differences in lipophilicity and pharmacokinetic parameters of the drugs.

An ionizable chromophoric reagent for the analysis of primary amine-containing drugs by capillary electrophoresis

We found that ofloxacin acyl chloride is a potential chromophoric reagent for labeling amino analytes for capillary electrophoresis. Ofloxacin acyl chloride has a tertiary amino function in its structure and the derivatives from ofloxacin acyl chloride reacting with amino analytes can be ionized by an acid treatment and analyzed by simple capillary zone electrophoresis. Ofloxacin acyl chloride was used to derivatize model analytes (without chromophore) of amantadine (amino drug), tranexamic acid (non-protein amino carboxylic acid), glycine, and methionine (protein amino acids). The resulting derivatives were analyzed by capillary zone electrophoresis with ultraviolet detection (300 nm). The detection limits of the analytes studied were in the range of 1.0-2.5 microM (S/N = 3, injection 3 s). The precision (relative standard deviation) and accuracy (relative error) of the method for intra- and inter-day analyses of the analytes were respectively below 4.5% and 3.9%. Application of the method to the analysis of tranexamic acid in plasma proved feasible.

Allometric analysis of ciprofloxacin and enrofloxacin pharmacokinetics across species

The purpose of this study was to examine the allometric analysis of ciprofloxacin and enrofloxacin using pharmacokinetic data from the literature. The pharmacokinetic parameters used were half-life, clearance and volume of distribution. Relationships between body weight and the pharmacokinetic parameter were based on the empirical formula Y = aW(b), where Y is half-life, clearance or volume of distribution, W the body weight and a is an allometric coefficient (intercept) that is constant for a given drug. The exponential term b is a proportionality constant that describes the relationship between the pharmacokinetic parameter of interest and body weight. A total of 21 different species of animals were studied. Results of the allometric analyses indicated similarity between clearance and volume of distribution as they related to body weight for both drugs. Results of the current analyses indicate it is possible to use allometry to predict pharmacokinetic variables of enrofloxacin or ciprofloxacin based on body size of species. This could provide information on appropriate doses of ciprofloxacin and enrofloxacin for all species.

The efficacy of enrofloxacin, alone or combined with metronidazole, in the therapy of canine leishmaniasis

We evaluated the efficacy of enrofloxacin, alone or combined with metronidazole, against Leishmania infantum. The in vitro activity of this fluoroquinolone was assessed using two different methods: a direct test aimed at assessing the drug activity on the parasite, and an indirect test aimed at evaluating the drug effect on macrophage killing, lymphomonocyte activation and nitric oxide production. An in vivo test was also performed on 36 dogs with leishmaniasis, subdivided into three groups, one treated with enrofloxacin, another with enrofloxacin plus metronidazole, and a control group with meglumine antimoniate. The direct test did not show any action of enrofloxacin on the parasite, while the indirect testing showed an enhancement of macrophage killing and an increase in nitric oxide production. These findings show that enrofloxacin does not exert a direct anti-leishmanial activity in vitro. However, on the basis of the positive immunostimulation results shown in vitro and the clinical improvement, particularly of the cutaneous lesions, obtained in several dogs in the in vivo trial, the use of enrofloxacin in association with a specific anti-leishmanial drug can be proposed in the therapeutic protocol of canine leishmaniasis.

Antimicrobial drug delivery in food animals and microbial food safety concerns: an overview of in vitro and in vivo factors potentially affecting the animal gut microflora

This review provides an overview of considerations particular to the delivery of antimicrobial agents to food animals. Antimicrobial drugs are used in food animals for a variety of purposes. These drugs may have therapeutic effects against disease agents, or may cause changes in the structure and/or function of systems within the target animal. Routes of administration, quantity, duration, and potency of an antimicrobial drug are all important factors affecting their action(s) and success. Not only might targeted pathogens be affected, but also bacteria residing in (or on) the treated food animals, especially in the intestines (gastrointestinal tract microflora). Resistance to antimicrobial agents can occur through a number of mechanisms. The extent to which resistance develops is greatly affected by the amount of drug [or its metabolite(s)] a bacterium is exposed to, the duration of exposure, and the interaction between an individual antimicrobial agent and a particular bacterium. The impact of antimicrobial agents on the emergence of resistance in vitro and in vivo may not readily correlate.

Phytotoxicity to and uptake of enrofloxacin in crop plants

Phytotoxicity of enrofloxacin on crop plants Cucumis sativus, Lactuca sativa, Phaseolus vulgaris and Raphanus sativus was determined in a laboratory model: the effect of 50, 100 and 5000 microgl(-1) were evaluated after 30 days exposure by measuring post-germinative growth of primary root, hypocotyl, cotyledons and leaves. Concentrations between 50 and 5000 microgl(-1) induced both toxic effect and hormesis in plants, by significantly modifying both length of primary root, hypocotyl, cotyledons and the number/length of leaves. A toxic effect is induced by high concentration (5000 microgl(-1)), while hormesis occurs at low concentrations (50 and 100 microgl(-1)). A continuum between toxic effect and hormesis is found in the four plant species. Both toxic effect and hormesis can be related to an efficient plant drug uptake, in the order of microgg(-1). Plants are able to metabolize enrofloxacin into ciprofloxacin, as also happens in animals; Cucumis, Lactuca and Phaseolus biologically convert about one quarter of stored enrofloxacin. The ecological implication of enrofloxacin contamination in terrestrial environments is discussed.

Comparative pharmacokinetics of enrofloxacin and tissue concentrations of parent drug and ciprofloxacin after intramuscular administrations of free and liposome-encapsulated enrofloxacin in rabbits

Pharmacokinetic properties and tissue concentrations of enrofloxacin and ciprofloxacin were compared after intramuscular (i.m.) administrations of free and liposome-encapsulated enrofloxacin at the dose of 5 mg/kg body weight (bw). Twelve healthy adult New Zealand white rabbits were used in the experiment. Blood samples were obtained at 10, 20, 40, 60 and 90 min and 2, 4, 6, 8 and 12 h and tissue samples were collected 24 h after injection. Concentrations of drugs in serum were determined by high-performance liquid chromatography. Pharmacokinetics were best described by a two-compartment open model. Results indicated that absorption rate was slow, peak concentration was higher (P < 0.05), and the time to peak concentration (tmax congruent with 1.5 h) was significantly longer (P < 0.05) for liposome-encapsulated enrofloxacin (LEE) when compared with free enrofloxacin. Values of elimination half-life (t1/2beta = 12.9 h) and mean residence time (MRT = 17.6 h) of liposome-encapsulated enrofloxacin were longer (P < 0.05) and total clearance (Cl = 0.43 l/h/kg) was lower than those of free form. Moreover, the distribution volume at steady-state (Vd(ss) = 14.4 l/kg) of enrofloxacin administered encapsulated into liposomes was significantly higher (P < 0.05) than that of free enrofloxacin (FE). The tissue levels of enrofloxacin and ciprofloxacin after LEE injection were not different (P > 0.05) from FE. In conclusion, the result of present study suggest that LEE may be a beneficial and valuable formulation in the treatment of infectious diseases caused by sensitive pathogens in animals, providing sustained drug release from injection side and prolonged therapeutic serum concentrations after i.m. administration.

Activity-bioavailability balance in oral drug development for a selected group of 6-fluoroquinolones

A nomogram is proposed to select the best candidate in drug development studies with quinolones and is intended to substitute other possible models. The nomogram is referred to as an activity-bioavailability balance (ABB) because it includes the following two criteria: ABB = [(1/gm MIC drug candidate)/ (1/gm MIC ciprofloxacin)].[(F(calc) drug candidate)/( F(calc) ciproflaxacin)]. The in vitro activity of a group of 4'N-alkyl-ciprofloxacin derivatives was determined together with that of ciprofloxacin, initially against some reference strains and subsequently against 159 clinical isolates of eight selected species. The inverse of the geometric mean of the lowest concentration of drug at which the original inoculum was reduced to no more than two colonies (1/gm MIC), as an antimicrobial activity parameter, and the absolute oral bioavailability index (F(calc)), as predicted from in situ intestinal absorption rate constants, were used for calculation of the ABB values, which ranged from 0.1 to 17 for the species and compounds tested. Ciprofloxacin was the best candidate only against Escherichia coli, whereas 4'N-methyl- and/or 4'N-ethyl-ciprofloxacin showed better or much better ABB values than the model drug, and can be selected as potential drug candidates against the remaining clinical strains. The procedure described could be a useful technique for further drug development studies.

In vitro antimicrobial susceptibility of 183 Pseudomonas aeruginosa strains isolated from dogs to selected antipseudomonal agents

During the years from 1993 to 2000, 183 strains of Pseudomonas aeruginosa were isolated from different pathological specimens originating from dogs. Antimicrobial susceptibility patterns against 10 antipseudomonal agents were obtained on 183 P. aeruginosa strains. In vitro antimicrobial susceptibility testing was performed using the disk diffusion method (Kirby-Bauer). Antimicrobial susceptibility profiles showed that among beta-lactam antibiotics, imipenem was the most active compound. Out of the 183 strains tested, 96.7% were sensitive to imipenem. Cefoperazone showed good in vitro activity against 86.9% of the tested strains. Against ceftazidime, 77.0% of strains showed sensitivity. An old penicillin, carbenicillin, gave only 71.6% sensitive strains. Sensitivity to amikacin was 87.4% and it was 83.1% to gentamicin. Pipimedic acid, a first-generation quinolone, was the least active compound of all those tested, 47.0% were resistant. The in vitro sensitivity against enrofloxacin showed that 71.0% strains were sensitive and 26.2% showed resistance. Almost all strains tested, 93.4%, were susceptible to ciprofloxacin and marbofloxacin. Besides imipenem, the quinolone antibiotics, marbofloxacin and ciprofloxacin were the most effective against P. aeruginosa strains isolated from dogs.

The disposition kinetics, urinary excretion and dosage regimen of ciprofloxacin in buffalo calves (Bubalus bubalis)

The disposition kinetics, urinary excretion and a dosage regimen for ciprofloxacin after a single intravenous administration of 5 mg/kg was investigated in 5 healthy buffalo calves. The disposition kinetics were best fitted to a three-compartment open model. After 1 min, the concentration of ciprofloxacin in plasma was 8.50 +/- 0.39 microg/ml and the minimum therapeutic concentration was maintained for 10 h. The elimination half-life and volume of distribution were 3.88 and 0.08 h and 3.97 +/- 0.22 L/kg, respectively. The total body clearance and T/P ratio were 0.709 +/- 0.025 L/kg per h and 6.13 +/- 0.54, respectively. Approximately 28.3% of the total administered dose of ciprofloxacin was recovered in urine within 24 h of administration. To maintain a minimum therapeutic plasma concentration of 0.10 microg/ml, a satisfactory intravenous dosage regimen of ciprofloxacin, computed on the basis of disposition kinetic data obtained in healthy buffalo calves, would be 3 mg/kg repeated at 12 h intervals.

In vitro antibacterial activity of enrofloxacin and ciprofloxacin in combination against Escherichia coli and staphylococcal clinical isolates from dogs

The objective of the study was to determine the in vitro interaction between enrofloxacin and ciprofloxacin against Escherichia coli and staphylococcal isolates from dogs. The microdilution checkerboard assay was used to determine the interaction of the drugs against 50 E. coli and 50 beta-haemolytic staphylococcal clinical isolates. The checkerboard assay revealed that the activity of enrofloxacin and ciprofloxacin was additive against E. coli and staphylococcal clinical isolates. It was concluded that for bacterial species against which ciprofloxacin is more potent than enrofloxacin, the in vivo transformation of enrofloxacin to ciprofloxacin may enhance the efficacy of enrofloxacin, if additivity of the drugs is confirmed in vivo.

Comparison of fluoroquinolone pharmacokinetic parameters after treatment with marbofloxacin, enrofloxacin, and difloxacin in dogs

Plasma, urine, and skin drug concentrations were determined for dogs (n=12) given five daily oral doses of marbofloxacin (MAR) (2.75 mg/kg), enrofloxacin (ENR) (5.0 mg/kg) or difloxacin (DIF) (5.0 mg/kg). Concentrations of the active metabolite of ENR, ciprofloxacin (CIP), were also determined. The three-period, three-treatment crossover experimental design included a 21-day washout period between treatments. Area under the plasma drug concentration vs. time curve (AUC0-last, microg/mLxh of MAR was greater than for ENR, CIP, ENR/CIP combined, and DIF. Maximum concentration (Cmax) of MAR was greater than ENR, CIP, and DIF. Time of maximum plasma concentration (Tmax) was similar for MAR and DIF; Tmax occurred earlier for ENR and later for CIP. Plasma half-life (t1/2) of MAR was longer than for ENR, CIP, and DIF. Urine concentrations of DIF were less than MAR or ENR/CIP combined, but urine concentrations of MAR and ENR/CIP combined did not differ. DIF skin concentrations were less than the concentrations of MAR or ENR/CIP combined 2 h after dosing, but skin concentrations of MAR and ENR/CIP combined did not differ.

Factors influencing the bioavailability of peroral formulations of drugs for dogs

The oral route is presently the preferred route of drug delivery. Poor oral bioavailability results in variable concentrations of drugs in the plasma and variable pharmacological responses, in addition to higher product costs. The unique canine physiology, anatomy and biochemistry makes designing canine dosage forms a challenging exercise. This article reviews the physicochemical, physiological, pharmacokinetic, pharmacological and formulation factors that can influence the drug availability of the oral formulations in dogs in an effort to provide a source of data to aid development of canine drug products with superior bioavailability.