Pharmacokinetics of enrofloxacin in Korean catfish (Silurus asotus)

The enrofloxacin pollution control from fish to environment

Enrofloxacin (ENR) is used to prevent and treat fish diseases widely. However, its pollution is increasing public concern on human health and aquatic ecosystem safety. This review aims to find its pollution mechanisms and control way. It is found: (1) The excessive ENR administration is the main source, the sediment ENR escaping from photolysis is the secondary ENR pollution source; (2) The ENR-rich fishes were benthic lipid-rich fishes which can simultaneously absorb administration ENR and sediment ENR, the ENR bioaccumulation is positively related to the fish habitats ENR level and fish lipids content; (3) The ENR t1/2 varies with fish age, body weight, feedstuff lipids and crude fiber level, temperature, salinity, administration mode and dose; Consequently, the first control way is to conduct the minimum inhibitory concentration ENR, combining herbal medicines with antibacterial and detoxification functions. The second way is to develop the enrichment and removal techniques for sediment ENR.

Plasma and tissue kinetics of enrofloxacin and its metabolite, ciprofloxacin, in yellow catfish (Pelteobagrus fulvidraco) after a single oral administration at different temperatures

The objective of this study was to examine the pharmacokinetic (PK) properties of enrofloxacin (EF) and its metabolite, ciprofloxacin (CF), in yellow catfish (Pelteobagrus fulvidraco) after a single oral dose of EF at 20 mg/kg at 20, 25, and 30 °C. Samples were collected at pre-designed time points and determined by high-performance liquid chromatography with a fluorescent detector. Results showed that most concentrations of EF and CF in plasma and tissues at the same time point at different temperatures were statistically significant. With the increase in temperature, the terminal half-life (T_1/2λz) of EF and CF was first reduced from 20 to 25 °C but elevated from 25 to 30 °C in plasma, muscle + skin, gill, liver, and kidney, respectively. The area under the plasma concentration-time curves (AUC_last) of EF were all decreased in plasma, muscle + skin, and gill except for that of EF in the liver and kidney. However, the AUC_last and the apparent metabolic rate of CF were exhibited first elevated and then decreased trend. The apparent volume of distribution (Vz_F) of EF was first reduced from 20 to 25 °C but increased at 30 °C. The apparent total body clearance (CL_F) of EF was increased from 0.15 to 0.32 L/h·kg with the temperature elevation. These indicated that increased temperature markedly affected the PKs of EF and CF in yellow catfish. Through in-depth analysis, the EF dosage of 20 mg/kg is appropriate to use in yellow catfish at 20 and 25 °C but 30 °C.

Metabolism and residue differences of Enrofloxacin between the brain and peripheral tissues and the resulting brain damages in crucian carp (Carassius auratus var. Pengze)

This study aimed to explore the metabolism and residue differences of Enrofloxacin (ENR) at two doses between the brain and peripheral tissues (liver, kidney, and muscle) along with the brain damages caused by ENR in crucian carp (Carassius auratus var. Pengze). The concentrations of ENR in tissues were determined using a validated high-performance liquid chromatography (HPLC) analysis. Relying on the hematoxylin-eosin (HE) staining method, brain damages caused by the drug were evaluated by the section of pathological tissue. Metabolism and residue results showed that ENR could be detected in the brain throughout the experiment both at median lethal dose (LD₅₀ at 96 h, 1949.84 mg/kg) and safe dose (SD, 194.98 mg/kg), as well as in the three peripheral tissues. The maximum residue at LD₅₀ followed the decreasing order of liver >kidney > brain > muscle. Although the C_max of ENR at SD in the brain was significantly lower than that in other peripheral tissues (p < .05), it still reached 41.91 μg/g. The T_1/2 of ENR in brain tissue at the same dose was both shorter than that in peripheral tissues. At LD₅₀ , the amount of ENR residues in brain was lower than that in peripheral tissues on the whole, except that it had been higher than in the muscle for the first 3 h. At SD, the drug residue in brain tissue was lower than that in peripheral tissues from 12 h to 960 h, but it exceeded the muscle and kidney at 1 h and 6 h, respectively. At 960 h, the residual amount of ENR at SD in the brain was 0.09 μg/g, while it was up to 0.15 μg/g following the oral administration at LD₅₀ . Demonstrated by the HE staining, there were pathological lesions caused by ENR in the brain at LD₅₀ , which were characterized by sparse neural network and increased staining of glial cells. The present results indicated that metabolism and residue of ENR in crucian carp were affected by the tissue type and drug dosage, and the ENR could also bring about histopathological changes in the brain.

Plasma and muscle tissue disposition of enrofloxacin in Nile tilapia (Oreochromis niloticus) after intravascular, intraperitoneal, and oral administrations

The aim of the study was to investigate the plasma and muscle pharmacokinetic of enrofloxacin (ENR) and its active metabolite ciprofloxacin (CIP) in Nile tilapia (Oreochromis niloticus) following single intravascular (IV), intraperitoneal (IP), or oral (PO) administration at 30 ± 1 °C. In this study, 234 healthy Nile tilapia (120-150 g) were used. The fish received a single IV, IP, or PO treatment of ENR at a dose of 10 mg/kg. The plasma and muscle tissue concentrations of ENR and CIP were measured using high-performance liquid chromatography with fluorescence detection and were evaluated using non-compartmental analysis. The elimination half-life, volume of distribution at steady state, and total body clearance of ENR were 21.7 h, 2.69 L/kg, and 0.09 L/h/kg, respectively. The peak plasma concentrations of ENR after IP or PO administration were 6.11 and 4.21 µg/mL at 0.25 and 2 h, respectively. The bioavailability of ENR for IP or PO routes was 78% and 86%, respectively. AUC_{(0-120)muscle}/AUC_{(0-120)plasma} ratios following the IV, IP, or PO administrations were 1.43, 1.49, and 1.07, respectively. CIP was detected after all routes, but the AUC_0-last ratios of CIP to ENR were <1.0% for plasma and muscle. ENR was detected up to 120 h following the IV, IP, or PO administrations. The long residence time of ENR after single IV, IP, or PO administration ensured the plasma concentration was ≥1 × MIC for bacteria with threshold MIC values of 0.92, 0.72, and 0.80 μg/mL over the whole 120 h observed. However, further studies are necessary to determine the optimum pharmacokinetic/pharmacodynamics data of ENR for the treatment of infections caused by susceptible bacteria in tilapia.

Identification and characterization of SaRpAMP, a 60S ribosomal protein L27-derived antimicrobial peptide from amur catfish, Silurus asotus

Aquatic freshwater fish like catfish, Silurus asotus, lives in microbe-rich environments, which enable this fish to develop necessary defense mechanisms. Antimicrobial peptides, along with other innate immune factors, are regarded as an important group in this defense. An antimicrobial peptide, which was isolated from the skin of S. asotus, was identified as a C-terminal fragment of 60S ribosomal protein L27 from S. asotus. The peptide was, then, designated Silurus asotus 60S ribosomal protein L27-derived antimicrobial peptide, SaRpAMP. Primary structure analyses and cDNA cloning revealed that SaRpAMP was 4185.36 Da and composed of 33 amino acids (AAs). Its precursor had a total of 136 AAs containing a pro-sequence of 103 AAs encoded by the nucleotide sequence of 512 bp that comprises a 5' untranslated region (UTR) of 32 bp, an open reading frame (ORF) of 411 bp, and a 3' UTR of 69 bp. Secondary structure analyses showed that SaRpAMP had two α-helices with turns and coils and an amphiphilic structure, a finding consistent with the 3D model of the peptide. SaRpAMP exhibited potent antibacterial activity comparable to piscidin 1, a powerful positive control. Its antimicrobial activity against fungus C. albicans was relatively weak. The antimicrobial activity of SaRpAMP was not diminished by heat treatment and changes in pH but was abolished by proteolytic enzyme digestion. Membrane permeability assays suggested that SaRpAMP interacts with both the outer and inner bacterial membranes. This was consistent with the results of lipid titration and quenching of Trp fluorescence that demonstrated SaRpAMP's interaction with acidic liposomes. Collectively, these findings suggest that the identified peptide, SaRpAMP, was the first antimicrobial peptide reported to be derived from the C-terminal region of 60S ribosomal protein L27. The findings also suggest that the action mechanism of SaRpAMP involved the interaction of the peptide with the bacterial membranes.

Pharmacokinetics of danofloxacin in African catfish (Clarias gariepinus) after intravenous and intramuscular administrations

The plasma pharmacokinetics of danofloxacin was studied in healthy African catfish (Clarias gariepinus) following a single intravenous (IV) and intramuscular (IM) administration of 10 mg/kg at 22 °C. Catfish were divided into two groups (each group containing 78 fish), then danofloxacin mesylate (10 mg/kg) was administered IV (into the caudal vein) in Group 1 and IM (into the right epaxial muscle) in Group 2, and blood was obtained from the caudal vein before (0 h) and after (0.25, 0.5, 1, 2, 4, 8, 12, 24, 36, 48, 72 and 96 h) of drug administration. High-performance liquid chromatography was used for the determination of plasma concentration, and a non-compartmental model was used for the analysis of pharmacokinetic parameters. After IV administration, elimination half-life (t_1/2λz, 24.49 h), mean residence time (MRT, 30.14 h), volume of distribution at steady state (Vdss, 1.07 L/kg) and total body clearance (CL_T, 0.035 L/h/kg) were determined. After IM administration, t_1/2λz, MRT, peak concentration (C_max), time to reach C_max and bioavailability were 47.64 h, 61.06 h, 5.22 µg/mL, 1 h and 67.12%, respectively. After IM administration, danofloxacin showed good bioavailability and long t_1/2λz. The favourable pharmacokinetic characteristics after IM administration support the use of danofloxacin for the treatment of susceptible bacterial infections in catfish.

Pharmacokinetics and tissue residues of enrofloxacin in the largemouth bass (Micropterus salmoides) after oral administration

The study was carried out to evaluate the pharmacokinetic disposition of enrofloxacin (ENF) with a single dose of 20 mg/kg after oral administration in largemouth bass (Micropterus salmoides) at 28°C. The concentrations of ENF and of its metabolite ciprofloxacin (CIP) in plasma, liver, and muscle plus skin in natural proportions were determined using HPLC. The concentration-time data for ENF in plasma were best described by a two-compartment open model. After oral administration, the maximum ENF concentration (C_max ) of 10.99 μg/ml was obtained at 0.60 hr. The absorption half-life (T_1/2Ka ) of ENF was calculated to be 0.07 hr whereas the elimination half-life (T_1/2β ) of the drug was 90.79 hr. The estimates of area under the plasma concentration-time curve (AUC) and apparent volume of distribution (Vd/F) were 1,185.73 μg hr/ml and 2.21 L/kg, respectively. ENF residues were slowly depleted from the liver and muscle plus skin of largemouth bass with the T_1/2β of 124.73 and 115.14 hr, respectively. Very low levels of ciprofloxacin were detected in the plasma and tissues. A withdrawal time of 24 days was necessary to ensure that the residues of ENF + CIP in muscle plus skin were less than the maximal residue limit (MRL) of 100 μg/kg established by the European Union.

Pharmacokinetic/pharmacodynamic relationship of enrofloxacin against Aeromonas hydrophila in crucian carp (Carassius auratus gibelio)

The pharmacokinetic (PK) properties of enrofloxacin (ENR) and its metabolite ciprofloxacin (CIP) were investigated in crucian carp following oral administration at different dose levels (5, 10, 20, 40 mg/kg body weight). The disposition kinetics of ENR was found to be linear over the dose range studied. Serum half-lives ranged from 64.56 to 72.68 hr. The in vitro and ex vivo activities of ENR in serum against a pathogenic strain of Aeromonas hydrophila were determined. In vitro and ex vivo bactericidal activity of ENR was concentration dependent. Dosing of 10 mg/kg resulted in an AUC/minimum inhibitory concentration (MIC) ratio of 368.92 hr and a C_max /MIC ratio of 7.23, respectively, against A. hydrophila 147 (MIC = 0.48 μg/ml), indicating a likely high level of effectiveness in clinical infections caused by A. hydrophila with MIC value ≤ 0.48 μg/ml. Modeling of ex vivo growth inhibition data to the sigmoid Emax equation provided the values of AUC_24 hr /MIC required to produce bacteriostasis, bactericidal activity, and elimination of bacteria, these values were 21.70, 53.01, and 125.21 hr, respectively. These findings in conjunction with MIC₉₀ data suggested that ENR at the dose of 7.81 mg/kg predicted a positive clinical outcome and minimize the risk of emergence of resistance.

Magnolol protects channel catfish from Aeromonas hydrophila infection via inhibiting the expression of aerolysin

Aeromonas hydrophila is a common zoonotic pathogen which can cause several infections both in human and animals, particular aquatic animals. Antibiotics have been widely used in the treatment of A. hydrophila infections, however, the development of resistance has limited the treatment for these infections. There is an urgent need for novel agents and strategies against these infections. Aerolysin, a pore-forming toxin secreted by most pathogenic A. hydrophila, is known to contribute to the pathogenesis of A. hydrophila infections. Therefore, aerolysin has been identified as a potential target for drug discovery. In this paper, we found that magnolol, a natural compound without anti -A. hydrophila activity, could significantly inhibit the hemolytic activity of A. hydrophila culture supernatants by inhibiting the transcription of the aerolysin encoding gene aerA at low concentrations. Furthermore, the survival assay showed that magnolol could significantly reduce the mortality induced by A. hydrophila infection in channel catfish (Ictalurus punctatus). Taken together, these findings provide a potent agent against A. hydrophila infections.

Pharmacokinetics and tissue distribution of enrofloxacin after single intramuscular injection in Pacific white shrimp

The pharmacokinetic properties and tissue distribution of enrofloxacin (EF) were investigated after single intramuscular (i.m.) dose of 10 mg/kg body weight (b.w.) in Pacific white shrimp at 22 to 25°C. EF and its metabolite ciprofloxacin (CF) were determined by high-performance liquid chromatography. After i.m. administration, EF was absorbed quickly, and the peak of EF concentration (C_max ) reached at first time point in hemolymph. The volume of distribution V_d(area) of EF was 3.84 L/kg, indicating that the distribution of EF was good. The area under the concentration-time curve (AUC) of EF was 90.1 and 274.2 μg hr/ml in muscle and hepatopancreas, respectively, which was higher than 75.8 μg hr/ml in hemolymph. The EF elimination was slow in muscle and hepatopancreas with the half-life (T_1/2β ) of 52.3 and 75.8 hr, respectively. CF, the mainly metabolite of EF, was detected in hemolymph, muscle and hepatopancreas. The C_max was 0.030, 0.013 and 0.218 μg/ml, respectively. Based on a minimum inhibitory concentration (MIC) of 0.006-0.032 μg/ml for susceptible strains, EF i.m. injected at a dose 10 mg/kg could be efficacious against common pathogenic bacteria of Pacific white shrimp.

Pharmacokinetics of enrofloxacin after oral, intramuscular and bath administration in crucian carp (Carassius auratus gibelio)

The pharmacokinetics of enrofloxacin (ENR) was studied in crucian carp (Carassius auratus gibelio) after single administration by intramuscular (IM) injection and oral gavage (PO) at a dose of 10 mg/kg body weight and by 5 mg/L bath for 5 hr at 25°C. The plasma concentrations of ENR and ciprofloxacin (CIP) were determined by HPLC. Pharmacokinetic parameters were calculated based on mean ENR or CIP concentrations using WinNonlin 6.1 software. After IM, PO and bath administration, the maximum plasma concentration (C_max ) of 2.29, 3.24 and 0.36 μg/ml was obtained at 4.08, 0.68 and 0 hr, respectively; the elimination half-life (T_1/2β ) was 80.95, 62.17 and 61.15 hr, respectively; the area under the concentration-time curve (AUC) values were 223.46, 162.72 and 14.91 μg hr/ml, respectively. CIP, an active metabolite of enrofloxacin, was detected and measured after all methods of drug administration except bath. It is possible and practical to obtain therapeutic blood concentrations of enrofloxacin in the crucian carp using IM, PO and bath immersion administration.

Tracking aquaculture-derived fluoroquinolones in a mangrove wetland, South China

Aquaculture in mangrove wetlands has been developed rapidly, causing various environmental problems (e.g., antibiotic residue). In the present study, the levels and distributions of a well-known class of antibiotics (fluoroquinolones; FQs), including norfloxacin (NOR), ciprofloxacin (CIP), and enrofloxacin (ENR), were examined in sediment and mangrove plant (Aegiceras corniculatum) from a mangrove wetland in the Zhanjiang Mangrove National Nature Reserve, South China. NOR and CIP were detected in all sediment samples, with concentrations ranging from 4.3 to 64.2 ng/g and from 7.62 to 68.5 ng/g on a basis of dry weight (dw), respectively, whereas ENR was found with relatively lower frequency (<78%) and lower concentrations (<19.3 ng/g). Sediments in mangrove rhizosphere area contained considerably higher concentrations of all FQs (except for ENR). FQs were largely varied in mangrove plant tissues; NOR and ENR were not detected in leaf and root samples, respectively. CIP featured an increasing tendency from the root to the upper parts of plants, whereas a decreasing trend was found for NOR. Three bioconcentration factors (BCF_s) of FQs, including BCFs for roots (BCF_r), branches (BCF_b), and leaves (BCF_l) were calculated, and most of them exceeded 1. Especially for NOR, its BCF_r can reach up to 9.9, indicating that Aegiceras corniculatum has a strong ability to accumulate FQs from sediment and/or surrounding environment. For NOR and CIP, strong positive relationships were observed between BCF_r and concentrations in root, but no significant correlations were observed between BCF_r and root lipid of mangrove plant. More studies are needed to investigate the uptake mechanism of antibiotics in mangrove plants.

Pharmacokinetics of cefquinome in tilapia (Oreochromis niloticus) after a single intramuscular or intraperitoneal administration

The pharmacokinetics of cefquinome was studied in plasma after a single dose (10 mg/kg) of intramuscular (i.m.) or intraperitoneal (i.p.) administration to tilapia (Oreochromis niloticus) in freshwater at 30 °C. Ten fish per sampling point were examined after treatment. The data were fitted to two-compartment open models following both routes of administration. The estimates of total body clearance (CL/F), volume of distribution (Vd/F), and absorption half-life (T1/2ka ) were 0.049 and 0.037 L/h/kg, 0.41 and 0.33 L/kg, and 0.028 and 0.035 h following i.m. and i.p. administration, respectively. After i.m. injection, the elimination half-life (T1⁄2β ) was calculated to be 5.81 h, the maximum plasma concentration (Cmax ) to be 49.40 μg/mL, the time to peak plasma cefquinome concentration (Tmax ) to be 0.14 h, and the area under the plasma concentration-time curve (AUC) to be 204.6 μg h/mL. Following i.p. administration, the corresponding estimates were 6.05 h, 44.39 μg/mL, 0.17 h and 267.8 μg h/mL. The minimum inhibitory concentrations of cefquinome, determined for 30 strains of Streptococcus agalactiae isolated from diseased tilapia, ranged from 0.015 to 0.12 μg/mL. Results from these studies support that 10 mg cefquinome/kg body weight daily could be expected to control tilapia bacterial pathogens inhibited in vitro by a minimal inhibitory concentration value of ≤2 μg/mL.

Comparison of plasma and tissue disposition of enrofloxacin in rainbow trout (Oncorhynchus mykiss) and common carp (Cyprinus carpio) after a single oral administration

The aim of the study was to investigate the serum and tissue disposition of enrofloxacin and its active metabolite ciprofloxacin in rainbow trout (Oncorhynchus mykiss) and common carp (Cyprinus carpio) after a single oral administration at a dose of 10 mg kg(-1). Concentrations of enrofloxacin in the serum of rainbow trout showed high variability with two peaks at the third and 24th hour after administration. The highest concentrations were found in the liver. The curves of liver levels showed similar changes to the respective serum samples. In the muscles, enrofloxacin concentrations were also higher compared with the respective serum samples. Ciprofloxacin concentrations were lower and showed smaller variations in all investigated tissues. The serum and tissue concentrations of enrofloxacin and ciprofloxacin in common carp showed two peaks, with the first Cmax at the third hour after drug administration as in rainbow trout. Concentrations of both investigated substances were higher in the liver than in the serum. The differences in common carp were less pronounced in comparison with rainbow trout. Relatively high levels of both substances were found in the muscles. Seven days after treatment enrofloxacin concentrations in the serum and tissues were within the therapeutic levels for most of the sensitive microorganisms in trout. Lower concentrations of its metabolite ciprofloxacin were found in the investigated tissues at the last sampling point. Lower levels of both substances were found in carp.

Florfenicol depletion in edible tissue of rainbow trout, Oncorhynchus mykiss (Walbaum), and sea bream, Sparus aurata L

An increase in fish production has consequently brought an increase in infectious diseases in fish farms. The use of chemotherapic drugs is the most effective instrument against common bacterial agents. The number of registered drugs for use in aquaculture is limited and often veterinary practitioners resort to the off-label use of chemotherapic agents authorized for different food-producing animal species. Florfenicol is well known for its outstanding effect against various pathogenic bacteria affecting fish, and therefore, it may be a useful drug for off-label use in aquaculture. The aim of this study was to evaluate the depletion of florfenicol and its major metabolite, florfenicol amine, from the edible tissue of two fish species, rainbow trout and sea bream, following treatment with medicated feed at a dosage of 10 mg kg(-1) of bw day(-1) , for 10 consecutive days. At prefixed time points after the end of administration (0.25, 1, 2, 3, 4, 6, 7, 10, 14 and 21 days after treatment), edible tissues (muscle plus adherent skin) from 15 individuals in each group were collected and analysed by HPLC, to determine concentration of the drug in the tissue. On the basis of the obtained concentrations, withdrawal times of florfenicol in the two species were calculated. The results indicate that a drug withdrawal time of 500 °C-day, as established by Directive 2004/28/EC, for off-label drug use is more than satisfactory to guarantee the healthiness of fish products against the risk of drug residues.

Residues of fluoroquinolones in marine aquaculture environment of the Pearl River Delta, South China

Concentrations and distributions of selected fluoroquinolones (norfloxacin, ciprofloxacin and enrofloxacin) in water, sediments and nine kinds of fish species collected from 6 sites in two marine aquaculture regions of the Pearl River Delta, China, were analyzed by using high-performance liquid chromatography with fluorescence detector (HPLC). The results showed that the concentrations of ciprofloxacin and enrofloxacin were below the limits of quantification (LOQ) in all water samples except for norfloxacin. Norfloxacin and ciprofloxacin concentrations ranged from 1.88 to 11.20 ng g(-1) dry wt, 0.76-2.42 ng g(-1) dry wt in sediments collected from the Dapeng'ao region (sites 1-3) and ranged from 2.31 to 4.75 ng g(-1) dry wt, 1.26-1.76 ng g(-1) dry wt in sediments collected from the Hailing Island region (sites 4-6), respectively. However, no enrofloxacin was found in all sediment samples. The three fluoroquinolones (FQs) were detected in all fish samples, and the concentrations were higher in liver tissues than those in muscle tissues. The levels of norfloxacin were higher than ciprofloxacin and enrofloxacin in both liver and muscle tissues. Among the nine marine fish species, Siganus fuscescens from Hailing Island had a significantly high level of norfloxacin in liver tissue (254.58 ng g(-1) wet wt), followed by Sparus macrocephalus (133.15 ng g(-1) wet wt) from Dapeng'ao, and the lowest value was Lutianus argentimaculatus (5.18 ng g(-1) wet wt) from Hailing Island. The obtained results of FQs in present study do not represent a risk to the human health in Guangdong coastal area, based on the maximum residue limits (MRLs) established by Chinese Government and the acceptable daily intake (ADI) recommended by the Food and Agriculture Organization and World Health Organization (FAO/WHO).

Pharmacokinetics of enrofloxacin in allogynogenetic silver crucian carp, Carassius auratus gibelio

The pharmacokinetics of enrofloxacin (EF) was investigated after single intravenous (i.v.) and oral (p.o.) administration of 10 mg/kg body weight (b.w.) in 300 healthy allogynogenetic silver crucian carp at 24-26°C. The plasma concentrations of EF and its metabolite ciprofloxacin (CF) were determined by high-performance liquid chromatography. After i.v. administration, the plasma concentration-time data were described by an open two-compartment model. The elimination half-life (T(1/2β)), area under the concentration-time curve (AUC) and total body clearance of EF were 63.5 h, 239.6 μg·h/mL and 0.04 L/h/kg, respectively. Following p.o. administration, the plasma concentration-time data showed a double peak-shaped curve, indicating the possibility of enterohepatic recirculation of EF in allogynogenetic silver crucian carp. The maximum plasma concentration (C(max)), T(1/2β) and AUC of EF were 4.5 μg/mL, 62.7 h and 205.9 μg·h/mL, respectively. Absorption of EF was very good with a bioavailability (F) of 86%, which could be correlated with the unique structure of the alimentary canal in allogynogenetic silver crucian. CF, an active metabolite of EF, was not detected in this study.

Effects of enrofloxacin on cytochromes P4501A and P4503A in Carassius auratus gibelio (crucian carp)

Currently, although enrofloxacin (EF) as a widely used veterinary medicine has begun to apply to treating fish bacterial infections, the researches on the effects of EF on their main drug metabolic enzymes are limited. To investigate the effects of EF on fish cytochromes P450 (CYPs) 1A and 3A, the enzymatic activities and expressions (mRNA and protein) of crucian carp CYP1A and CYP3A after EF administration were examined. For CYP1A, in the in vivo experiments, EF exhibited potent inhibition on the CYP1A-related ethoxyresorufin-O-deethylase (EROD) activity, as well as CYP1A expressions at both protein and mRNA levels, at 24 h after administration with different EF dosages (3, 10, 30, and 60 mg/kg); Furthermore, CYP1A enzymatic activity and expressions at both protein and mRNA levels decreased more with increasing EF dosages. Additionally, the in vitro experimental results showed that, after incubated with microsomes, EF did not change the EROD activity through interacting directly with CYP1A. For CYP3A, the in vitro and in vivo experimental results demonstrated that EF could inhibit the CYP3A-related erythromycin N-demethylase activity in a time- and dose-dependent manner, while it did not suppress CYP3A expressions at both protein and mRNA levels after administration with EF for a short period (no more than 24 h); however, after injection with EF at a high dose (10 mg/kg) for a long period, the CYP3A protein and mRNA reached their lowest levels at 96 and 48 h, respectively. These results indicate that EF can suppress CYP1A expressions in a dose-dependent manner, thereby inhibiting further its catalytic activity; meanwhile, both the interactions of EF with CYP3A and the expressions decrease (protein and mRNA) caused by EF contribute to the CYP3A inhibition.

Effects of light and microbial activity on the degradation of two fluoroquinolone antibiotics in pond water and sediment

Enrofloxacin (ENR) and ciprofloxacin (CIP) are two fluoroquinolone (FQ) antibiotics widely used to treat diseases of human beings and cultured animals. These two FQs are usually detected in the effluent of municipal sewage plants and related aquatic environments. The purpose of this study was to understand the fates of ENR and CIP in aquaculture pond water and a sediment slurry in a laboratory-scale experiment. Effects of light and microbial activity on the degradation of these two FQs were investigated. Results indicated that natural irradiation plays a major role in the degradation of ENR and CIP in pond water and the sediment slurry. The 50 % dissipation times (DT(50)) with non-sterile treatment were 0.01 and 18.4 d for ENR, and 0.04 and 17.3 d for CIP in the water and sediment slurry, respectively. On the other hand, the degradation of ENR and CIP under dark conditions was slow or even hindered, and all of their DT(50) values exceeded 100 d. These two FQs degraded faster in the sediment slurry than in pond water under dark conditions. Artificial ultraviolet (UV) and fluorescence light had similar effects on the degradation of ENR in the pond water and sediment slurry. Degradation of CIP was faster with UV than with fluorescence light treatment, while no such difference was found for ENR degradation. CIP was a degradation product of ENR under both light and dark conditions, and DT(50) values for both compounds were shorter in the presence of light. The phenomenon of biodegradation was observed during degradation of CIP in the sediment slurry under natural light.

Dispositions and residue depletion of enrofloxacin and its metabolite ciprofloxacin in muscle tissue of giant freshwater prawns (Macrobrachium rosenbergii)

Fates and residue depletion of enrofloxacin (ER) and its metabolite ciprofloxacin (CP) were examined in giant freshwater prawns, Macrobrachium rosenbergii, following either single oral (p.o.) administration of ER at a dosage of 10 mg/kg body weight (b.w.) or medicated-feed treatment at the feeding concentration of 5 g/kg of feed for five consecutive days. The concentrations of ER and CP in prawn muscle tissues were measured simultaneously using high-performance liquid chromatography (HPLC) equipped with a fluorescence detector. Muscle tissue concentrations of ER and CP were below the detection limit (LOD, 0.015 microg/g for ER; 0.025 microg/g for CP) after 360 and 42 h, following single p.o. administration respectively. Peak muscle concentration (C(max)) of ER was 1.98 +/- 0.22 microg/g whereas CP was measurable at concentrations close to the detection limit of the analytical method after p.o. administration at a single dosage of 10 mg/kg b.w. The concentration of ER in prawn muscle tissue with respect to time was analyzed with a non-compartmental pharmacokinetic model. The elimination half-life and area under the curve of ER were 39.33 +/- 7.27 h and 168.7 +/- 28.7 microg x h/g after p.o. administration at a single dose of 10 mg/kg x b.w. respectively. In medicated-feed treated group, ER was detectable in prawn muscle tissue 11 days postdosing at the dose of 5 g/kg of feed for five consecutive days, which is the value corresponding to the maximum residue limit (MRL) of ER in animal products. The maximum concentrations of ER and CP were 2.77 +/- 0.91 and 0.06 +/- 0.006 microg/g during medicated-feed treatment and postdosing respectively. The values of elimination half-life and absorption half-life of ER after single p.o. administration at a dosage of 10 mg/kg b.w. corresponded well with the values determined from medicated-feed treated group, showing 41.01 +/- 6.62 and 11.36 +/- 3.15 h respectively in M. rosenbergii. Based on data derived from this study, to avoid the ER residue in prawn muscle, it should take at least 11 days postcessation of medicated feed containing ER at the dose concentration of 5 g/kg of feed twice a day at a rate of 1% of total body weight for five consecutive days to wash out the drug from the muscle of M. rosenbergii.

Adverse effects of enrofloxacin when associated with environmental stress in Tra catfish (Pangasianodon hypophthalmus)

The aim of this study was to assess the adverse effects of enrofloxacin (EF) on Tra catfish, Pangasianodon hypophthalmus, in relation with density stress. Fish were held at 40, 80 or 120 fish m(-3) and fed with pellets containing either 1 g kg(-1) EF or no EF. Antibiotic exposure lasted 7d and all fish were fed without EF for another 7-d recovery period. Fish were sampled at 3, 7, 8, 10 and 14 d after the beginning of EF exposure. Lipid peroxidation (LPO) and total glutathione (GSH) levels, catalase (CAT), glutathione-s-transferase (GST) and acetylcholine-esterase (AChE) activities were assessed in gill, brain, liver and muscle. At day 7, LPO levels in gills of EF-fish reared at low or high density were significantly more than 5-fold higher than their respective control. On the contrary, LPO in gills of EF-fish reared at medium density was significantly 3-fold lower than the control fish. Similarly, CAT activities in gills of EF-fish reared under low or high density were higher than in their control groups, while this activity was lower in EF-fish of the medium density group. AChE activities in muscles of EF-fish reared at low or high density were lower than controls at days 3 and 7, respectively. These results suggest that EF exposure may lead to disorders like lipid peroxidation and neural dysfunction in fish. However, when reared under lower stress condition (medium density), they may cope better with EF-induced stress than chronically stressed fish (low or high density).

Altered pharmacokinetics of enrofloxacin in experimental models of hepatic and renal impairment

We investigated the effects of hepatic and renal impairment on the pharmacokinetics of enrofloxacin in Sprague-Dawley rats. Experimental hepatic and renal failure were induced by carbon tetrachloride (CCL(4)) and 5/6 nephrectomy, respectively. After intravenous dosing of enrofloxacin (10 mg/kg), plasma concentrations of enrofloxacin were measured using liquid chromatograph/mass spectrometry. There was no significant effect of hepatic impairment on enrofloxacin pharmacokinetics. However, renal impairment markedly prolonged elimination half life (t(1/2lambdaz)) of enrofloxacin (P < 0.05), comparing with respective control. Total body clearance (Cl(b)) and volume of distribution at steady state (V(ss)) were significantly decreased (P < 0.05) by renal impairment. In conclusion, these results suggested that renal impairment could affect the pharmacokinetics of enrofloxacin.