Antibacterial activity of amoxicillin in vitro and its oral bioavailability in broiler chickens under the influence of 3 water sanitizers.

The interaction of 3 water sanitizers (sodium hypochlorite, iodine-polyvinylpyrrolidone, and citrate) utilized in poultry production on antibacterial activity and bioavailability of amoxicillin trihydrate (AMX) were studied. Sanitizers were mixed with AMX in prepared water, the resulting substances were regarded as amoxicillin-sanitizer products (ASP). First, the in vitro antibacterial activity of each ASP was compared to that of AMX. Then, pharmacokinetics (PK) of ASP and AMX diluted in prepared water, were carried out in broiler-chickens. Amoxicillin or ASP (20 mg/kg) from different concentrations of sanitizers was directly placed into the chicken's crop and blood samples were taken. Basic PK parameters were obtained. Serum activity/concentrations of AMX were assessed by agar diffusion and corroborated with high performance liquid chromatography. Results show that ASP of AMX/sodium hypochlorite decrease both, the antimicrobial activity of in vitro AMX and its relative bioavailability (Fr) assessed with the maximum serum concentration (Cmax), the area under the concentration-time curve, and the mean residence time (MRT) (3.80 µg/mL, 2.70 µg/mL·h, and 0.59 h, respectively), compared to the AMX administered alone (12.54 µg/mL, 44.02 µg/mL·h, and MRT 2.78 h). ASP from amoxicillin/ionophore, reduced the Cmax (10.62 µg/mL), Fr (94.67%), and MRT (2.07 h), at the highest tested concentrations. In contrast, the 2 highest concentrations of the citrate sanitizer increased the Cmax (15.07 and 15.47 µg/mL), Fr (119 and 132%), and MRT (3.32 and 4.06 h) and their in vitro antimicrobial activity. Interactions between the tested water sanitizers and AMX modify the Cmax, Fr, MRT of the latter, altering the PK/pharmacodymanic ratios for a time-dependent antibiotic. Results also reveal that the use of amoxicillin trihydrate administered through the drinking water does not meet the required PK/pharmacodymanic ratios. Thus, it is here postulated that this antibiotic should be administered at least twice a day and that its interaction with water sanitizers should be considered.

Efficacy assessment of an intramammary treatment with a new recrystallized enrofloxacin vs ceftiofur and parenteral enrofloxacin in dairy cows with nonsevere clinical mastitis.

A recrystallized form of enrofloxacin as dehydrate-HCl (enro-C) was assessed for bacteriological and clinical cure efficacies in Holstein-Friesian cows affected of nonsevere clinical mastitis. Treatments were enro-Csusp (n = 81), treated with a pharmaceutical suspension of enro-C/quarter; group enro-Cpd (n = 80) treated as above, but using enro-C powder suspended in water; group CF (n = 65), treated with ceftiofur HCl/quarter; and group enroR (n = 66), treated with standard enrofloxacin solution (5 mg/kg, intramuscular). Cows had a mean milk production of 31 L/day and were 2-3 lactational periods old. Treatments were administered every 24 hr for 3 days. Groups treated with enro-C exhibited statistically significant (p > .05) better clinical cure as compared to groups treated with CF or enroR (95.06%, 96.25%, 67.79%, and 57.55%, for enro-Csusp , enro-Cpd , CF, and enroR , respectively). In contrast, probability of bacteriological cure was not statistically different among treatments. Yet, the outstanding clinical and bacteriological cure rates obtained for enro-C for nonsevere cases of mastitis is superior to previously reported data for parenteral enrofloxacin and other antibacterial-intramammary treatments. Impact of using enro-C on the rate and pattern of bacterial resistance, somatic cell counts and milk electric conductivity, must be studied. Also, the use of enro-C for complicated cases of mastitis should be studied and milk withdrawal times must be accurately established.

Ixodicide activity of Eysenhardtia polystachya against Rhipicephalus (Boophilus) microplus.

The objective of this study was to evaluate the acaricidal effect of 2 compounds extracted from Eysenhardtia polystachya in vitro, namely coatlines and matlalines. Each extract was obtained by aqueous extraction in a nitrogen atmosphere. Engorged adult females of an amitraz-resistant strain of Rhipicephalus (Boophilus) microplus were used to produce larvae and to carry out the adult immersion test (AIT), while larvae were assayed using the larval packet test (LPT). After exposure to coatlines or matlalines, the mortality of larvae and engorged females, as well as the reproductive parameters of adult ticks were assessed. Coatlines were not lethal against larvae and did not decrease reproductive parameters. Conversely, matlalines showed a 90 to 100% efficacy against adults and larvae at all concentrations tested and a reduction of 76.41 to 80.64% oviposition and a 48.02 to 54.86% reduction in egg hatchability. Therefore, the acaricidal activity of matlalines was more efficient. Further studies are required to elucidate both the mode of action of matlalines as well the structure-activity relationships responsible for the observed differential efficacy between these 2 related isoflavans against the cattle tick.

Physicochemical characterization and pharmacokinetics in broiler chickens of a new recrystallized enrofloxacin hydrochloride dihydrate.

Enrofloxacin, a key antimicrobial agent in commercial avian medicine, has limited bioavailability (60%). This prompted its chemical manipulation to yield a new solvate-recrystallized enrofloxacin hydrochloride dihydrate entity (enroC ). Its chemical structure was characterized by means of mass spectroscopy, Fourier transformed infrared spectroscopy, X-ray powder diffraction, and thermal analysis. Comparative oral pharmacokinetics (PK) of reference enrofloxacin (enroR ) and enroC in broiler chickens after oral administration revealed noticeable improvements in key parameters and PK/PD ratios. Maximum serum concentration values were 2.61 ± 0.21 and 5.9 ± 0.42 µg/mL for enroR and enroC , respectively; mean residence time was increased from 5.50 ± 0.26 h to 6.20 ± 0.71 h and the relative bioavailability of enroC was 336%. Considering Cmax /MIC and AUC/MIC ratios and the MIC values for a wild-type Escherichia coli O78/H12 (0.25 µg/mL), optimal ratios will only be achieved by enroC (Cmax /MIC = 23.6 and AUC/MIC = 197.7 for enroC ; vs. Cmax /MIC = 10.4 and AUC/MIC = 78.1 for enroR ). Furthermore, enroC may provide in most cases mutant prevention concentrations (Cmax /MIC ≥ 16). Ready solubility of powder enroC in drinking water at concentrations regularly used (0.01%) to provide an additional advantage of enroC in the field. Further development of enroC is warranted before it can be recommended for clinical use in veterinary medicine.

Pharmacodynamic evaluation of a reference and a generic toltrazuril preparation in broilers experimentally infected with Eimeria tenella or E. acervulina.

Abstract 1. The aim of this study was to investigate the effects on pigmentation, faecal oocyst output, immune responsiveness and reactive oxygen species (ROS) generation following treatment with either the reference toltrazuril (Baycox) or a generic preparation (gen-TTZ), during an experimental Eimeria tenella (Et) or E. acervulina (Ea) infection of 210 Ross broiler chickens. 2. Results showed a significant difference on the anticoccidial efficacy 6 d after treating infected animals with Baycox (Et: 99.69% and Ea: 99.52%) or gen-TTZ (Et:85.71% and Ea 81.81%). 3. Gen-TTZ-treated animals were less strongly carotenoid-pigmented than Baycox-treated broilers. Mean plasma carotenoid concentrations were significantly higher in groups treated with Baycox than in broilers given gen-TTZ. 4. Treatment of animals with Baycox led to a significant decrease in ability of the peripheral blood mononuclear cells to produce ROS in contrast to gen-TTZ-treated groups. Baycox, but not generic toltrazuril, increased IL-10 and decreased tumour necrosis factor alpha (TNF-α) concentrations in chickens infected with E. tenella and E. acervulina. 5. It is suggested that differences in anticoccidial efficacy may be observed when using a generic toltrazuril product. Hence, in addition to plasma profiles of drugs, standardised clinical control tests may be necessary for generic formulations, particularly if other parameters are important to achieve a better control of coccidiosis.

Pharmacokinetics of an injectable long-acting parenteral formulation of doxycycline hyclate in pigs.

Based on its ideal PK/PD ratios, doxycycline hyclate (DOX-h), a time-dependant antibacterial, is ideally expected to achieve sustained plasma drug concentrations at or slightly above the MIC level for as long as possible between dosing intervals. Pursuing this end, a poloxamer-based matrix was used to produce a 10% long-acting injectable preparation (DOX-h-LA) and its serum concentrations vs. time profile investigated after its injection to pigs in the pericaudal s.c. by parallel design. Results were compared with the forced oral bolus dose and i.v. pharmacokinetics of DOX-h. For this study, 12 recently weaned pigs per group were included in this trial, and a dose of 20 mg/kg was injected in all cases. DOX-h-LA showed the greatest values for bioavailability (115.38%); maximum serum concentration (Cmax) value was 1.5 ± 0.2 with a time to reach Cmax of 3.41 ± 0.04 h and an elimination rate constant of 70.93 ± 0.87( ) h. Considering minimum effective serum concentration of 0.5 µg/mL, a dose interval of at least 5 days can be achieved for DOX-h-LA, whereas p.o. and i.v. dosing of DOX-h may only last 11 and 15 h, respectively. Pigs were slaughtered on day 30 after this trial, and no visible remnants of the preparation were detected neither fibrosis was observed after a thorough macroscopic and histopathological analysis.

Serum and tissue concentrations of doxycycline in broilers after the sub-cutaneous injection of a long-acting formulation.

1. The antibacterial agent doxycycline hyclate (Dox) is usually administered to broilers in drinking water or as a feed supplement. Parenteral injection is not the usual route for administration, so a long-acting formulation (Dox-LA) was tested to evaluate if serum concentrations can achieve the pharmacokinetic/pharmacodynamic (PK/PD) ratios regarded as adequate for the drug. 2. A poloxamer-based matrix was used to provide Dox-LA. Serum and tissue concentrations of Dox vs time were determined in two day-old broilers after subcutaneous (SC) injection of Dox-LA or oral administration of a single bolus of aqueous Dox (Dox-PO), at a dose of 20 mg/kg. Weight gain, feed conversion rate, haematological variables, aspartate aminotransferase and alanine aminotransferase activities, blood urea and creatinine were determined and compared for Dox-LA with Dox-PO and non-medicated controls. 3. Dox-LA had a high relative bioavailability (1200%). Maximum serum concentrations were not statistically different (5·1 ± 1·1 µg/ml for Dox-LA and 6·1 ± 1.4 µg/ml for Dox-PO), but half-life of Dox-LA was much greater than the value obtained for Dox-PO (73·0 ± 0·9 h and 2·0 ± 0·02 h, respectively). Tissue concentrations were higher, and stayed higher for longer periods in the Dox-LA group. 4. In conclusion, considering the minimum effective serum concentration against Mycoplasma spp is 0·5 µg/ml, a dose-interval of 180 h can be achieved with Dox-LA, but only for 24 h after Dox-PO. Better PK/PD ratios for Dox-LA should result in improved clinical outcomes compared with Dox-PO.

Plasma concentrations resulting from florfenicol preparations given to pigs in their drinking water.

Florfenicol administered through the drinking water has been recommended as a metaphylactic antibacterial drug to control outbreaks of respiratory diseases in pigs caused by strains of Actinobacillus pleuropneumoniae and Pasteurella multocida, yet it is difficult to pinpoint in practice when the drug is given metaphylactically or therapeutically. Further, pigs are likely to reject florfenicol-medicated water, and plasma concentrations of the drug are likely to be marginal for diseases caused by Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus. The reported minimal inhibitory concentration (MIC) values for these organisms show a breakpoint of 2 to 3 µg/mL. An experiment was conducted during September and October 2009. One hundred twenty healthy crossbred pigs (Landrace-Yorkshire), weighing 23 ± 6.2 kg, were used in this trial. They were randomly assigned to 5 groups, with 3 replicates of 8 animals/group. Two commercial preparations of florfenicol were administered through the drinking water at 2 concentrations (0.01 and 0.015%). Water intake was measured before and after medication, and plasma concentrations of florfenicol were determined by HPLC. Considerable rejection of florfenicol-medicated water was observed. However, plasma florfenicol concentrations were of a range sufficient for a methaphylaxis approach to preventing disease by bacteria, with MIC breakpoints of ≤ 0.25 µg/mL. Decreased efficacy as a metaphylactic medication should be expected for bacteria with MIC >0.25 µg/mL, considering the reported existence of bacteria resistant to florfenicol and the natural resistance of Streptococcus suis or E. coli to this drug.

Pharmacokinetics of disodium fosfomycin in broilers and dose strategies to comply with its pharmacodynamics versus Escherichia coli.

The objective of this study was to determine, in broilers, which modality of disodium fosfomycin (DF) administration and at what dose the best pharmacokinetic (PK) profile could be obtained, taking as reference a 110 field bacterial strains of Escherichia coli minimum inhibitory concentration survey. The DF was administered via drinking water either ad libitum or at a higher concentration having 1 h of water restriction to build up thirst in the birds (loading dose). Dosages tested were 10, 20, 40, and 80 mg/kg per administration, either once or twice daily. Birds included were 24-d-old Cornish broilers randomly assigned to 16 groups of 200 birds per group and 3 replicates per group. The PK of DF was determined after ad libitum administration of either a single- or double-loading dose or after an initial loading dose followed by ad libitum medication. Also, PK after i.v. administration was studied in separate groups. Serial blood samplings were performed in all groups. Serum obtained was analyzed for DF and a possible active metabolite by means of a microbiological agar diffusion assay. The DF showed a short elimination half-life (approximately 2 h after oral loading administration) with a rapid clearance (1.23 to 1.42 mL/kg per h). Apparent volume of distribution-area under the curve values were also low (10 and 80 mg/kg=0.25 L/kg and 0.22 L/kg, respectively). Considering a minimum inhibitory concentration level that inhibited 90% of total strains of 8 µg/mL for E. coli, it is concluded that single-loading administration at 10, 20, 40, and 80 mg/kg complies poorly with sustained serum concentrations over a dosing interval of 24 h. Doses of 10 and 20 mg/kg twice a day also were insufficient to attain therapeutic concentrations. Useful serum concentrations of DF to treat outbreaks of susceptible E. coli require an initial loading dose of 40 mg/kg, followed by an ad libitum medication of 40 mg/kg 8 h later (80 mg/kg per d).

Electroencephalographic evaluation of gold wire implants inserted in acupuncture points in dogs with epileptic seizures.

The purpose of this study was to evaluate both, clinically and with electroencephalographic (EEG) recordings, the effect of gold wire implants in acupuncture points in dogs with uncontrolled idiopathic epileptic seizures. Fifteen dogs with such diagnosis were enrolled in the study. A first EEG recording was performed in all dogs under anaesthesia with xylazine (1mg/kg) and propofol (6 mg/kg) before the treatment protocol, and a second EEG was performed 15 weeks later. Relative frequency power, intrahemispheric coherence available through EEG, number of seizures and seizure severity were compared before and after treatment using a Wilcoxon signed-rank test. There were no significant statistical differences before and after treatment in relative power or in intrahemispheric coherence in the EEG recording. However, there was a significant mean difference in seizure frequency and seizure severity between control and treatment periods. After treatment, nine of the 15 dogs (60%) had at least a 50% reduction in seizures frequency during the 15 weeks established as follow-up of this treatment.

Circadian serum concentrations of tylosin in broilers after feed or water medication.

1. Because tylosin is a time-dependent antibacterial agent, and because feeding and drinking of broilers decreases in late afternoon and ceases in the dark, it was hypothesised that serum concentrations of this drug are greatly reduced during the dark period. 2. The trial was carried out in a commercial poultry house, under standard broiler husbandry conditions, with food and water withdrawn from 22:00 until 07:00 h next morning and exposed to a natural light cycle of 13L:11D. 3. Broilers were given tylosin tartrate, in either feed or water, for 5 d as follows: 100, 200 and 300 ppm in feed, equivalent to 12.6, 25.2 and 37.8 mg/kg/d, respectively; and 200 and 400 mg/l in drinking water, equivalent to 51 to 102 mg/kg/d, respectively. 4. At 07:00 h on d 4, and for the next 40 h, hourly serum samples were obtained and analysed for tylosin by means of a microbiological assay. 5. Day vs night concentrations of tylosin expressed as area under the curve (AUC) in all groups revealed greater values during the day. The highest AUC and AUC(24)/minimal inhibitory concentration (MIC) ratio were obtained in the group medicated with 400 mg/l and the corresponding lowest values were found in the group medicated with 100 ppm in feed. 6. In conclusion, tylosin did not reach therapeutic serum concentrations during the dark period, at all dose rates tested when administered in feed or water. A sustained release form of this drug is needed to solve this inadequacy of tylosin medication in broilers.

Pharmacokinetic study of an injectable long-acting parenteral formulation of doxycycline hyclate in calves.

Doxycycline hyclate (DOX-h) can be regarded as a time-dependant antibacterial. Hence, a parenteral long-acting formulation may be regarded as more pharmacologically sound. A poloxamer-based matrix was used to produce a long-acting injectable preparation (DOX-h-LA) and its serum concentrations vs. time profile investigated after its s.c. injection to calves. Serum concentrations profiles for such a prepartion were compared to the corresponding profiles obtained with an aqueous formulation of DOX-h injected either i.m. or i.v. in 10 calves in a crossover study at dose of 10mg/kg, with washout periods. DOX-h-LA showed the greatest values for bioavailability (602%); maximum serum concentration (C(max)) value was 1.99microg/mL with a time to reach C(max) (T(max)) of 25h and an elimination half-life of 40.81h. Considering minimum effective serum concentration of 0.5microg/mL a dose-interval of 80h can be achieved for DOX-h-LA, and only 9.7h and 17h after the i.v. or i.m. administration of DOX-h, respectively.

Design of two liquid Ibuprofen-poloxamer-limonene or menthol preparations for dermal administration.

The purpose of our study was to prepare liquid forms of 20% ibuprofen in 30% poloxamer 407, while avoiding gel formation and to assess their drug diffusion-penetration (permeation) into the skin. Two series of poloxamer-based formulations were prepared, both containing ibuprofen and one of two terpenes: d-limonene and 1-menthol. A rheological characterization of all preparations made allowed their grouping in two modalities: gels and fluids. Data revealed a statistically superior enhanced permeation terpene-dependent of ibuprofen in fluid preparations, specially the one containing d-limonene. Cumulative permeation in 24 hr was 2500 micro g/cm(2) and 4500 micro g/cm(2) for the 1-menthol and d-limonene, respectively, for fluid preparations as compared with 2000 micro g/cm(2) and 1600 micro g/ cm(2) for d-limonene and 1-menthol on gels and only 1200 micro g/cm(2) of the control solution (p < 0.05). Results postulate that a liquid 30% poloxamer-based preparation of ibuprofen with d-limonene is possible and that it may be useful as a topical preparation of ibuprofen.

Pharmacokinetics and renal toxicity of three once-a-day doses of amikacin in cows.

Pharmacokinetic variables of amikacin in cows were determined after administration of amikacin sulphate either intravenously (IV) or intramuscularly (IM) at a dose of 25 mg/kg per day for three days. Amikacin concentrations at time zero and maximum serum concentrations were 240.8 microg/mL and 122.53 microg/mL, respectively. The elimination half-life remained unchanged during the three days of administration (T1/2beta = 1.33 +/- 0.029 h for the IV route and T1/2beta = 2.75 +/- 0.38 h for the IM route). Apparent volumes of distribution suggest limited distribution out of the central compartment (VdAUC = 0.154 +/- 0.005 L/kg; Vdc = 36.50 +/- 2.35 L; Vdss = 0.092 +/- 0.004 L/kg). Bioavailability after IM administration was 95%. Serum profiles of urea, creatinine, albumin, electrolytes and pH after 5-day treatment with amikacin at a dose of 25 mg/kg per day IM revealed no changes. Assessment of diffusion of amikacin to milk by a commercially available screening method to detect antibiotic residues revealed that amikacin could not be detected by the fifth milking period after the last treatment. These results suggest that it would be rational to use a large single-daily dose of amikacin for future clinical trials in cows.

Sustained availability of trimethoprim in drinking water to achieve higher plasma sulphonamide-trimethoprim antibacterial activity in broilers.

(1) In order to make trimethoprim (TMP) available to broilers throughout the day, a sustained release formulation (SRF) of the drug in the form of granules was added to the water tank that supplies drinking water. (2) Broilers were initially dosed with sulphachloropiridazine-TMP (SCP-TMP 5:1) and then further medicated throughout the day, achieving in the end a dose of 30 mg/kg each of SCP and TMP (group A). Group B received a preparation with the same dose of SCP and TMP (1:1) as group A, but administered as a single dose without the SRF of TMP. Group C received the customary SCP-TMP 5:1 preparation (30 and 6 mg/kg, respectively). Water tanks were completely consumed in 3 to 4 h. (3) Broilers were bled at different times and concentration of antibacterial activity in serum determined by correlating the composite antibacterial activity of SCP and TMP with actual concentrations of these drugs by means of a microbiological agar diffusion assay. (4) Time vs serum concentrations of activity were higher in group B; the increments in the maximum serum concentration for group B over groups A and C being 39 and 67%, respectively. (5) However, the sustained concentration of activity over time, measured as the area under the cu)rve, was highest in group A. Group B had higher values for area under the curve than group C. (6) An additional dose of TMP to achieve 30 mg/kg of both SCP and TMP improves the serum concentration of this combination over the customary 5:1 proportion. The best values for sustaining antibacterial activity were obtained using a 1:1 ratio as in group A. The use of a SRF as in group A may translate into better clinical results.

Serum activity/concentration profiles of a sustained-released formulation of sulphathiazole-trimethoprim (2.5:1) in calves.

Thirty-six two-week-old healthy Holstein-Friesian calves weighing between 52 and 58 kg were divided at random into three groups of 12; group A calves were given a single oral bolus containing 2.5 g sulphathiazole and 1 g trimethoprim in a sustained-release formulation; group B received the same doses of the drugs but the trimethoprim was not in a sustained-release formulation; group C received a bolus containing 2.5 g sulphathiazole and 0.5 g conventional trimethoprim. Blood samples were collected at intervals for two days, the serum was separated and the composite antibacterial activity profiles of the mixture were analysed by an agar-diffusion microbiological method. The mean maximum activities in the serum of the three groups were 23.4 microg/ml in group A, 9.25 microg/ml in group B and 8.01 microg/ml in group C. The mean areas under the curves of the serum activity time curves were 838 microg/ml/hour in group A, 216 microg/ml/hour in group B and 182 microg/ml/hour in group C.

Pharmacokinetics and clinical efficacy of cefotaxime for the treatment of septicaemia in dogs.

Considering the already known pharmacological features of cefotaxime, a study with two approaches of pharmacokinetics and clinical efficacy in septicaemic dogs was carried out. Pharmacokinetic variables were defined for doses of 10 mg/kg, and 20 mg/kg, utilising a quantitative bacteriological analysis. Values for half-life (T1/2 beta) at 10 mg/kg were 0.8, 1.48 and 1.52 h for the i.v., s.c. and i.m. routes, respectively. Corresponding values for the 20 mg/kg dose for the same routes were 0.8, 1.49 and 1.53 h, respectively. Relatively fast clearance (ranging from 0.58 to 0.64 L/kg/h) allowed a maximum dose interval of 12 h. The above-stated doses of cefotaxime were administered i.v. to 40 cases of septicaemia, clinically divided into 20 moderately severe cases treated with 10 mg/kg i.v., of cefotaxime bid, and 20 severe ones, treated with 20 mg/kg i.v. of cefotaxime bid. Injections continued until a previously defined criterion of 'clinically recovered' was obtained. Thereafter, a follow-up treatment was established using the same dose and dose-interval but through the s.c. route. Due to the apparent volumes of distribution obtained (ranging from 0.48 to 0.51 L/kg), considering the overall clinical efficacy obtained (90% for the 10 mg/kg dose and 75% for the 20 mg/kg dose), and due to the rapid improvement observed after a few doses of the drug (1.8 to 2.5 doses to 'clinical improvement'), it is safe to postulate such doses of cefotaxime as excellent choices for the treatment of septicaemia in dogs.