Ex vivo antibacterial activity of levofloxacin against Escherichia coli and its pharmacokinetic profile following intravenous and oral administrations in broilers

In vitro and ex vivo antibacterial activity of levofloxacin against Pasteurella multocida and Escherichia coli isolated from rabbits (Oryctolagus cuniculus) - A preliminary study

Levofloxacin veterinary formulations are available in Argentina, China and India for the use in dogs, cattle, pig and sheep, but not currently in the rabbit. Only the extra-label use in rabbits is possible. Levofloxacin is not labelled for veterinary use in the EU or the USA. The activity of levofloxacin against rabbit pathogens Pasteurella multocida (P. multocida) and Escherichia coli (E. coli) was evaluated. Minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were determined in broth and serum for 10 P. multocida isolates and 5 E. coli isolates from rabbits. One isolate of each bacterial species was used for the time-killing curve study in vitro and ex vivo. In vitro AUC24 /MIC ratios were used for building the inhibitory pharmacodynamic Imax model. The P. multocida MIC were 0.008-0.5 μg/mL, MBC - 0.015-0.5 μg/mL. Escherichia coli MIC was 0.008-0.03 μg/mL and MBC - 0.03-0.25 μg/mL. Bacterial counts were reduced to the limit of detection after 24 h with levofloxacin concentrations of 2 MIC and higher. All serum samples from rabbits treated with levofloxacin eliminated the bacteria within 24 h. AUC24 /MIC ratios for bacteriostatic, bactericidal and bacterial elimination effects for P. multocida and E. coli isolates were 21, 29 and 75 h and 27, 32 and 60 h, respectively. Proposed daily doses against P. multocida (MIC = 0.015 μg/mL) and E. coli (MIC = 0.03 μg/mL) isolates were calculated as ≤0.91 and ≤1.43 mg/kg, respectively. Fluoroquinolones are categorized by WHO as 'highest priority critically important antimicrobials'. Considering the increasing importance of antimicrobial stewardship, antimicrobials from a lower importance category that are active against the isolate of interest should be used in preference to fluoroquinolones. Fluoroquinolone use in veterinary medicine should be based on antimicrobial susceptibility testing in order to mitigate the risk to public health and prevent the spread of bacterial resistance.

Kinetics of bactericidal potency with synergistic combination of allicin and selected antibiotics

Synergistic therapy against the resurgence of bacterial pathogenesis is a modern trend for antibacterial chemotherapy. The phytochemical allicin, found in garlic extract is a commendable antimicrobial agent that can be used in synergistic combination with modern antibiotics. Determination of optimal antibacterial combination for the target species is vital for maximizing efficacy, lowering toxicity, total eradication of the bacterial cells and minimization of the risk of resistance generation. In this present investigation, Hill function-based pharmacodynamics models were employed to elaborate various time-kill kinetics parameters. The bactericidal potency of the synergistic combinations of allicin and individual antibiotic was assessed in comparison to their monotherapy application viz. using sole allicin and sole antibiotics (levofloxacin, ciprofloxacin, oxytetracycline, rifaximin, ornidazole and azithromycin) on actively growing Bacillus subtilis and Escherichia coli bacteria. Here, all the synergistic combinations showed significantly better (t-test p-value < 0.05) killing effect and biofilm reduction potential compared to their respective monotherapy application, where the highest killing effect was observed with rifaximin-allicin combination (kill rate was more than 5.5 h^-1). Moreover, the average inhibition potential to protein denaturation by the synergistic combination group was significantly higher (3.4 fold) than the sole antibiotic's group manifests reduction in the dose-related toxicity. The potential of synergism between antibiotics and allicin combination demonstrated greater killing efficiency at significantly lower concentration compared to monotherapy with increased kill rates in all cases.

Implications of Veterinary Medicine in the comprehension and stewardship of antimicrobial resistance phenomenon. From the origin till nowadays

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Antibiotic resistance is a well-known phenomenon with several implications

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The contribution of Veterinary Medicine is underestimated.

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It was believed that only livestock was responsible for antibiotic resistance.

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Companion animals, wild animals and environment are more involved than estimated.

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Educational tools for public and more veterinary specialists are needed.

Antimicrobial resistance (AMR) is defined by the entire scientific community as the major threat for human health and it is responsible for an increase in morbidity and mortality rates. The reasons behind this phenomenon are complex and the solution is achievable only considering the One Health approach, that encompasses the integration and implementation of human health, veterinary medicine and environmental status. Authors aimed to write this review to summarize to readers the three milestones of One-Health, underlying the most important topics in which veterinary medicine is mostly involved. Therefore, a short introduction about the history of AMR in veterinary medicine is provided, then more detailed aspects about the impact of AMR related to pets, food producing animals, wild animals and environment are discussed. Finally, some critical aspects about current and future issues are considered.

Quantification of persister formation of Escherichia coli leveraging electronic cell counting and semi-mechanistic pharmacokinetic/pharmacodynamic modelling

BACKGROUND

Persister formation of Escherichia coli under fluoroquinolone exposure causes treatment failure and promotes emergence of resistant strains. Semi-mechanistic pharmacokinetic/pharmacodynamic modelling of data obtained from in vitro infection model experiments comprehensively characterizes exposure-effect relationships, providing mechanistic insights.

OBJECTIVES

To quantify persister formation of E. coli under levofloxacin exposure and to explain the observed growth-kill behaviour, leveraging electronic cell counting and pharmacokinetic/pharmacodynamic modelling.

METHODS

Three fluoroquinolone-resistant clinical E. coli isolates were exposed to levofloxacin in static and dynamic in vitro infection model experiments. Complementary to plate counting, bacterial concentrations over time were quantified by electronic cell counting and amalgamated in a semi-mechanistic pharmacokinetic/pharmacodynamic model (1281 bacterial and 394 levofloxacin observations).

RESULTS

Bacterial regrowth was observed under exposure to clinically relevant dosing regimens in the dynamic in vitro infection model. Electronic cell counting facilitated identification of three bacterial subpopulations: persisters, viable cells and dead cells. Two strain-specific manifestations of the levofloxacin effect were identified: a killing effect, characterized as a sigmoidal Emax model, and an additive increase in persister formation under levofloxacin exposure. Significantly different EC50 values quantitatively discerned levofloxacin potency for two isolates displaying the same MIC value: 8 mg/L [EC50 = 17.2 (95% CI = 12.6-23.8) mg/L and 8.46 (95% CI = 6.86-10.3) mg/L, respectively]. Persister formation was most pronounced for the isolate with the lowest MIC value (2 mg/L).

CONCLUSIONS

The developed pharmacokinetic/pharmacodynamic model adequately characterized growth-kill behaviour of three E. coli isolates and unveiled strain-specific levofloxacin potencies and persister formation. The mimicked dosing regimens did not eradicate the resistant isolates and enhanced persister formation to a strain-specific extent.

Levofloxacin in veterinary medicine: a literature review

A potent third-generation antimicrobial fluoroquinolone drug, levofloxacin was introduced into human clinical practice in 1993. Levofloxacin is also used in veterinary medicine, however its use is limited: it is completely banned for veterinary use in the EU, and used extralabel in only companion animals in the USA. Since its introduction to clinical practice, many studies have been published on levofloxacin in animal species, including pharmacokinetic studies, tissue drug depletion, efficacy, and animal microbial isolate susceptibility to levofloxacin. This literature overview highlights the most clinically relevant and scientifically important levofloxacin studies linked to the field of veterinary medicine.

Pharmacokinetics of levofloxacin mesylate in healthy adult giant panda after single-dose administration via different routes

The pharmacokinetics of levofloxacin mesylate in healthy adult giant panda is unknown. In this study, the pharmacokinetics of levofloxacin after intramuscular administration at a dose of 2 mg/kg and oral administration at a dose of 3 mg/kg in healthy adult giant pandas was determined. Levofloxacin concentrations in plasma were determined using liquid chromatography. In the levofloxacin intramuscular administration group, the absorption and elimination half-lives of the drug were determined to be 0.123 (range: 0.02) hr and 5.402 (range: 0.70) hr, respectively. In the levofloxacin oral administration group, the absorption and elimination half-lives were determined to be 0.325 (range: 0.02) hr and 7.143 (range: 0.63) hr, respectively. Furthermore, the blood-drug concentration of levofloxacin was found to be above 1 μg/ml after 8 hr of intramuscular administration and above 0.5 μg/ml after 12 hr of oral administration. In this study, HPLC conditions and pretreatment methods of plasma samples were optimized and a detection method was established. Our results indicated that in healthy adult giant pandas, levofloxacin was rapidly absorbed and slowly eliminated. This study will therefore provide to be a guide in veterinary research and will be helpful in the rational use of levofloxacin in giant panda.

Tissue Residues and Pharmacokinetic/Pharmacodynamic Modeling of Tiamulin Against Mycoplasma anatis in Ducks

The pharmacokinetics of tiamulin were studied in 2 groups of ducks (n = 6) after its oral administration at 2 different doses (30 and 60 mg/kg, respectively). Plasma concentrations of tiamulin were measured by high performance liquid chromatography at different time points up to 24 h post-administration. The maximum plasma concentrations were 0.77 and 2.32 μg/mL attained at 2 h (T_max) for 30 and 60 mg/kg, respectively. The elimination half-lives for these 2 doses were 3.54 and 6.34 h, respectively. The minimum inhibitory concentration for tiamulin against Mycoplasma anatis (M. anatis) strain 1340 was determined to be 0.06 μg/mL. The proper oral dose of tiamulin against M. anatis in ducks was calculated to be 35 mg/kg/day using the pharmacokinetic/pharmacodynamic modeling. Tiamulin was administered orally (40 mg/kg/day) to 30 ducks for 3 successive days to determine its residues in edible tissues and its preslaughter withdrawal time. The highest tiamulin residues were detected in the liver, followed by the muscle, whereas lower concentrations were detected in the skin and fat. The estimated withdrawal periods of tiamulin were 6, 5, 3, and 3 days for liver, muscle, skin, and fat, respectively. Therefore, an oral dosage regimen of 35 mg/kg/day should be adequate for tiamulin against M. anatis. We recommend a preslaughter withdrawal period of 6 days when ducks are treated with 40 mg tiamulin/kg/day, orally, for 3 days.

Levofloxacin pharmacokinetics and tissue residue concentrations after oral administration in Bilgorajska geese

1. The aim of this study was to assess the pharmacokinetics of levofloxacin, a third-generation fluoro-quinolone antimicrobial drug, in geese (n = 26) after either single intravenous or oral administration, and to evaluate the depletion profile in goose muscle, heart, liver, kidney and lung after a single oral dose.2. The pharmacokinetic study involved 16 geese which were randomly divided into two groups (n = 8/group), the first received levofloxacin (2 mg/kg) intravenously while the second was treated with orally (5 mg/kg). The tissue depletion study involved 10 geese which were dosed orally (5 mg/kg) and two animals were killed at different time-points in order to collect the selected tissues. Levofloxacin was quantified in all the matrices tested by a validated high-performance liquid chromatography (HPLC) method, using a spectrofluorimetric detector. The pharmacokinetics were analysed using a non-compartmental model.3. Plasma concentrations were quantified after up to 24 h in animals administered intravenously and up to 48 h after oral treatment. Levofloxacin was rapidly absorbed after oral administration (T_max = 0.38 h) showing high bioavailability (95.57 ± 20.61%). The drug showed a moderate volume of distribution (1.40 ± 0.28 ml/g) and rapid clearance (0.28 ± 0.06 ml/g/h). No statistical differences in estimates were found between the two different administration methods (P > 0.05). Drug residues were highest at 6 h and decreased constantly up to 48 h in all the selected tissues. Liver and kidney had the highest levofloxacin concentrations.4. According to the pharmacokinetic/pharmacodynamic surrogate index (AUC/MIC) the levofloxacin dose regimen (after oral administration) used in the present study could be active against bacteria at a minimum inhibitory concentration (MIC) > 0.24  μg/ml in geese. In addition, drug accumulation in the liver might be controlled using an estimated preliminary withdrawal time of 90 h.

Pharmacokinetics of levofloxacin in non-lactating goats and evaluation of drug effects on resistance in coliform rectal flora

This study aimed to evaluate the pharmacokinetics/pharmacodynamics (PK/PD) of levofloxacin in non-lactating goats. Using a randomized cross-over study design, each group of animals (n = 7) received 2 mg/kg of levofloxacin intravenously (IV) and subcutaneously (SC). Plasma concentrations of levofloxacin were quantified by High Performance Liquid Chromatography with fluorescence detector (HPLC-FL). Rectal swabs were collected prior and after the treatment to identify the main bacterial population and to evaluate in vitro antimicrobial susceptibility using minimal inhibitory concentration (MIC) method. Mean values of terminal half-life for IV and SC groups were 4.56 and 5.14 h, respectively. After SC administration, the peak plasma concentration was achieved at 2 h, with a C_max of 3681 ng/mL. Mean bioavailability was 92.12%. Bacteria isolation showed the presence of Escherichia coli (E. coli) that quickly becomes resistant to levofloxacin potentially rendering the drug ineffective. Results seem to suggest that levofloxacin is able to reach considerable plasma concentrations after both IV and SC administration, but it must be considered that both routes of administration can lead to a reversible selection of resistance in gastro-intestinal bacteria.

Pharmacokinetic profiles of levofloxacin after intravenous, intramuscular and subcutaneous administration to rabbits (Oryctolagus cuniculus)

Levofloxacin pharmacokinetic profiles were evaluated in 6 healthy female rabbits after intravenous (I/V), intramuscular (I/M), or subcutaneous (S/C) administration routes at a single dose of 5 mg/kg in a 3 × 3 cross-over study. Plasma levofloxacin concentrations were detected using a validated Ultra Performance Liquid Chromatography method with a fluorescence detector. Levofloxacin was quantifiable up to 10 h post-drug administration. Mean AUC0-last values of 9.03 ± 2.66, 9.07 ± 1.80, and 9.28 ± 1.56 mg/h*L were obtained via I/V, I/M, and S/C, respectively. Plasma clearance was 0.6 mL/g*h after I/V administration. Peak plasma concentrations using the I/M and S/C routes were 3.33 ± 0.39 and 2.91 ± 0.56 μg/mL. Bioavailability values, after extravascular administration were complete, - 105% ± 27% (I/M) and 118% ± 40% (S/C). Average extraction ratio of levofloxacin after I/V administration was 7%. Additionally, levofloxacin administration effects on tear production and osmolarity were evaluated. Tear osmolarity decreased within 48 h post-drug administration. All 3 levofloxacin administration routes produced similar pharmacokinetic profiles. The studied dose is unlikely to be effective in rabbits; however, it was calculated that a daily dose of 29 mg/kg appears effective for I/V administration for pathogens with MIC < 0.5 μg/mL.

Pharmacokinetic and tissue analyses of levofloxacin in sheep (Ovis aries Linnaeus) after multiple-dose administration

The aim of this study was to assess the pharmacokinetic profile of LFX in sheep after intravenous (IV) and oral (PO) administration of 2 mg/kg LFX once a day for 5 days and to evaluate its tissue depletion in the muscles, heart, liver, lungs, and kidneys. Twenty healthy female sheep were randomly divided into two equal groups. Each group was further randomly subdivided into two equal subgroups (n = 5). Group 1 was used for blood collection and underwent a crossover design (2 × 2 Latin square). Group 2 was randomly subdivided into two equal subgroups (n = 5) for IV and PO route respectively, and used for tissue collection. A single sheep was sacrificed at each time point and the organs were harvested. Samples were analyzed using a validated HPLC method with fluorescence detection. LFX administered orally was rapidly absorbed with a peak plasma concentration of 2866 ± 239 ng/mL and an absolute oral bioavailability of 114 ± 27.7%. The pharmacokinetic estimates were comparable between PO and IV administration. According to the pharmacokinetic/pharmacodynamic surrogate index (area under the curve / minimum inhibitory concentration) of 100-125, LFX has the potential to be an effective treatment for infections caused by bacteria with a MIC of 0.049-0.061 μg/mL. LFX was detected for up to 48 h in all the tissues samples. The kidney had the highest LFX concentration after IV and PO administration. The AUC_{tissue/plasma} ratio was lower than 1 in all tissues indicating absence of LFX tissue accumulation.

Pharmacokinetics, tissue residues, and ex vivo pharmacodynamics of tylosin against Mycoplasma anatis in ducks

The pharmacokinetics of tylosin were investigated in 3 groups of ducks (n = 6). They received a single dose of tylosin (50 mg/kg) by intravenous (IV), intramuscular (IM), and oral administrations, respectively. Plasma samples were collected at various time points to 24 hr post-administration to evaluate tylosin concentration over time. Additionally, tylosin residues in tissues and its withdrawal time were assessed using 30 ducks which received tylosin orally (50 mg/kg) once daily for 5 consecutive days. After IV administration, the volume of distribution, elimination half-life, area under the plasma concentration-time curve, and the total body clearance were 7.07 ± 1.98 L/kg, 2.04 hr, 19.47 µg hr/ml, and 2.82 L hr^-1  kg^-1 , respectively. After IM and oral administrations, the maximum plasma concentrations were 3.70 and 2.75 µg/ml achieved at 1 and 2 hr, and the bioavailability was 93.95% and 75.77%, respectively. The calculated withdrawal periods of tylosin were 13, 8, and 5 days for kidney, liver, and muscle, respectively. For the pharmacodynamic profile, the minimum inhibitory concentration for tylosin against M. anatis strain 1,340 was 1 µg/ml. The calculated optimal oral dose of tylosin against M. anatis in ducks based on the ex vivo pharmacokinetic/pharmacodynamic modeling was 61 mg kg^-1  day^-1 .

Toxicokinetic profile of fusarenon-X and its metabolite nivalenol in the goat (Capra hircus)

The main aim of this research was to evaluate the toxicokinetic characteristics of fusarenon-X (FX) and its metabolite, nivalenol (NIV), in goats. The amounts of FX and NIV in post-mitochondrial (S-9), microsomal and cytosolic fractions of diverse tissues of the goat were also investigated. FX was intravenously (iv) or orally (po) administered to goats at dosages of 0.25 and 1 mg/kg bw, respectively. The concentrations of FX and NIV in plasma, feces and urine were quantified by liquid chromatography tandem-mass spectrometry (LC-ESI-MS/MS). The concentrations of FX in plasma were quantified up to 8 h with both routes of administration. A large amount of NIV (metabolite) was quantifiable in plasma, urine and feces after both administrations. The C_max value of FX was 413.39 ± 206.84 ng/ml after po administration. The elimination half-life values were 1.64 ± 0.32 h and 4.69 ± 1.25 h after iv and po administration, respectively. In vitro experiments showed that the conversion FX-to-NIV mainly occurs in the liver microsomal fraction. This is the first study that evaluates the fate and metabolism of FX in ruminant species.

Kinetic simulation method of C-reactive protein in beagle dogs during acute inflammation

The half-life ( t1/2) of C-reactive protein (CRP) and its ability to stimulate weak inflammatory responses were investigated in beagle dogs. Four beagle dogs were administered 20 mg/kg indomethacin and blood was collected from the cephalic vein pre-dosing and at 24, 48, 72, 96, 144, 192, 240, 312, and 360 h post-administration. The serum concentrations of CRP were measured by enzyme-linked immunosorbent assay. The serum t1/2 was calculated using the equation 0.693/elimination rate constant. The serum concentration of CRP beyond 192 h post-administration declined to levels in the normal range. The t1/2 was 148.3 h, which is considered to be the essential t1/2 of CRP. The simulation of CRP serum concentrations at arbitrary times using the elimination rate constant obtained in this study became possible.