Analysis of Astragalus Polysaccharide Intervention in Heat-Stressed Dairy Cows' Serum Metabolomics

This experiment was conducted to investigate the effects of astragalus polysaccharides (APS) on serum metabolism of dairy cows under heat stress. Thirty healthy Holstein dairy cows were randomly divided into three groups (10 cows in each group). In the experimental group, 30 mL/d (Treatment I) and 50 mL/d (Treatment II) of APS injection were injected into the neck muscle respectively. Each stage was injected with APS for 4 days (8:00 a.m. every day) and stopped for 3 days. Serum hormone and antioxidant indexes of dairy cows were investigated. Through repeated measurement analysis of variance, the results have shown that cortisol (COR) (F = 6.982, p = 0.026), triiodothyronine (T3) (F = 10.005, p = 0.012) and thyroxine (T4) (F = 22.530, p = 0.002) at different time points were significantly different. COR showed a downward trend, T3 and T4 showed an upward trend. At each time point, different concentrations of APS have significant effects on COR (F = 30.298, p = 0.000 < 0.05), T3 (F = 18.122, p = 0.001), and T4 (F = 44.067, p = 0.000 < 0.05). However, there were no significant differences in serum insulin (INS), glucagon (GC) and heat shock protein 70 (HSP70) between different time points (p > 0.05) and at each time point (p > 0.05). Additionally, the results have also shown that there were also no significant differences in serum Superoxide dismutase (SOD), malondialdehyde (MDA) and lactate dehydrogenase (LDH) between different time points (p > 0.05) and at each time point (p > 0.05). However, the injection of APS had a significant impact on glutathione peroxidase (GSH-Px) (F = 9.421, p = 0.014) at different times, and showed a trend of rising first and then falling. At each time point, APS of different concentrations had no significant effect on GSH-Px (p > 0.05). Furthermore, we used gas chromatography-mass spectrometry (GC-MS) non-targeted metabolomics to determine the potential markers of APS for heat-stressed dairy cows. Twenty metabolites were identified as potential biomarkers for the diagnosis of APS in heat-stressed dairy cows. These substances are involved in protein digestion and absorption, glutathione metabolism, prolactin signaling pathway, aminoacyl-tRNA biosynthesis, pentose and glucuronate interconversions, and so on. Our findings suggest that APS have an effect on the serum hormones of heat-stressed dairy cows, and regulate the metabolism of heat-stressed dairy cows through glucose metabolism and amino acid metabolism pathways.

Pharmacokinetics of amoxicillin trihydrate in Thai swamp buffaloes (Bubalus bubalis): a pilot study

This study aimed to investigate the pharmacokinetic characteristics of amoxicillin (AMX) in Thai swamp buffaloes, Bubalus bubalis, following single intramuscular administration at two dosages of 10 and 20 mg/kg body weight (b.w.). Blood samples were collected at assigned times up to 48 h. The plasma concentrations of AMX were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The concentrations of AMX in the plasma were determined up to 24 h after i.m. administration at both dosages. The C_max values of AMX were 3.39 ± 0.18 μg/mL and 6.16 ± 0.18 μg/mL at doses of 10 and 20 mg/kg, respectively. The AUC_last values increased in a dose-dependent fashion. The half-life values were 5.56 ± 0.40 h and 4.37 ± 0.23 h at doses of 10 and 20 mg/kg b.w, respectively. Based on the pharmacokinetic data and PK-PD index (T > MIC), i.m. administration of AMX at a dose of 20 mg/kg b.w might be appropriate for the treatment of susceptible Mannheimia haemolytica infection in Thai swamp buffaloes.

Pharmacokinetic/pharmacodynamic integration and modelling of amoxicillin for the calf pathogens Mannheimia haemolytica and Pasteurella multocida

The antimicrobial properties of amoxicillin were determined for the bovine respiratory tract pathogens, Mannheima haemolytica and Pasteurella multocida. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and time-kill curves were established. Pharmacokinetic (PK)/pharmacodynamic (PD) modelling of the time-kill data, based on the sigmoidal Emax equation, generated parameters for three levels of efficacy, namely bacteriostatic, bactericidal (3log10 reduction) and 4log10 reduction in bacterial counts. For these levels, mean AUC(0-24 h) /MIC serum values for M. haemolytica were 29.1, 57.3 and 71.5 h, respectively, and corresponding values for P. multocida were 28.1, 44.9 and 59.5 h. Amoxicillin PK was determined in calf serum, inflamed (exudate) and noninflamed (transudate) tissue cage fluids, after intramuscular administration of a depot formulation at a dosage of 15 mg/kg. Mean residence times were 16.5 (serum), 29.6 (exudate) and 29.0 h (transudate). Based on serum MICs, integration of in vivo PK and in vitro PD data established maximum concentration (Cmax )/MIC ratios of 13.9:1 and 25.2:1, area under concentration-time curve (AUC0-∞ )/MIC ratios of 179 and 325 h and T>MIC of 40.3 and 57.6 h for P. multocida and M. haemolytica, respectively. Monte Carlo simulations for a 90% target attainment rate predicted single dose to achieve bacteriostatic and bactericidal actions over 48 h of 17.7 and 28.3 mg/kg (M. haemolytica) and 17.7 and 34.9 mg/kg (P. multocida).

Pharmacokinetics and oral bioavailability of amoxicillin in chicken infected with caecal coccidiosis

Chicken infected with caecal coccidiosis (Eimeria tenella) was used to evaluate the effect of coccidiosis on the pharmacokinetic and bioavailability of amoxicillin. The level of amoxicillin was estimated by high-performance chromatography (HPLC) to calculate the pharmacokinetic parameters and oral bioavailability. For i.v. injection of amoxicillin, Vd and CL were 0.29 and 0.27 (mg/kg)/(μg/mL)/h, respectively. Compared with healthy chicken, intravenous injection of amoxicillin in the infected chicken showed higher distribution and elimination constants, delayed clearance and statistically significant higher AUC and MRT. Oral administration in healthy chicken was accompanied by rapid absorption and high bioavailability with Tmax , Cmax and F about 1.03 h, 3.26 μg/mL and 40.2, respectively. Furthermore, oral administration in the infected chicken produced higher mean absorption time, delayed Tmax, lower Cmax, smaller AUC value and lower bioavailability (16.76). Based on these results, monitoring and adjustment of amoxicillin dosing could be practiced during the presence of coccidiosis. The measured Cmax values suggest the administration of 1.3-folds of the normal dose to maintain the normal maximal serum concentrations of amoxicillin in chicken infected with caecal coccidiosis.

Influence of the injection site on the pharmacokinetics of amoxicillin after intramuscular administration of a conventional and a long-acting formulation in sheep

The pharmacokinetics of amoxicillin (AMX) were investigated in sheep following intravenous (i.v.) and intramuscular (i.m) injection, comparing two different drug formulations, a conventional and a long-acting AMX-trihydrate suspension. For the i.m. application two different injections sites, the neck area and the hind limb were used to identify possible differences in the kinetic parameters related to the site of injection. A three-compartment open model could best describe AMX disposition after i.v. administration. Data analysis after i.m. administration of the conventional suspension at both injection sites revealed the occurrence of a flip-flop phenomenon, clearly indicating that absorption of AMX is the rate-limiting step of its overall disposition. A moderate effect of the injection site was observed with a tendency for the neck area to be advantageous, mainly in terms of rate rather than extent of absorption. Injection of the long-acting formulation led to a focal depot formation, thus yielding lower but remarkably prolonged serum AMX levels reflected in the respective terminal half-lives. The concentration-time profile of AMX after administration of the long-acting formulation was less affected by the injection site, but the low serum levels justify its use only in cases in which a high susceptibility of the involved bacterial population is confirmed.

Peripheral distribution of amoxicillin in sheep and influence of local inflammation

The pharmacokinetics of amoxicillin (AMX) in blood serum (SBS) and tissue cage fluid (TCF) was studied in sheep. Four tissue cages, prepared from silicone rubber tubing, were subcutaneously inserted in the neck area (two on each side) of the experimental animals and AMX was administered both intravenously (IV) and intramuscularly (IM) at the dose rate of 15mg/kg bodyweight. The impact of local inflammation on AMX distribution in TCF was studied after intra-cavity injection of a lambda carrageenan solution in one of the two tissue cages used after each administration. In contrast to the three-compartment AMX disposition after IV injection, two-compartment, absorption-limited pharmacokinetics was observed after IM administration. Non-inflamed and inflamed TCF data revealed, in all cases, the attainment of low, but prolonged concentrations and absence of an inflammation-induced effect on AMX penetration into and elimination from TCF.

The pharmacokinetics of single dose intramuscular amoxicillin trihydrate in tammar wallabies (Macropus eugenii)

Five tammar wallabies (Macropus eugenii) were injected intramuscularly with 10 mg/kg amoxicillin trihydrate. Serial blood samples were collected through to 26 hr postinjection. Plasma amoxicillin concentrations were measured using high-performance liquid chromatography. Pharmacokinetic parameters were estimated using noncompartmental analysis. The terminal half-life (1.77 +/- 0.40 hr) was comparable to that previously reported in domestic small ruminants. Without intravenous kinetic data, it is unclear whether the terminal phase is elimination- or absorption-dependent; both scenarios have been reported in domestic species. Plasma concentrations of amoxicillin remained above a reported minimum inhibitory concentration (MIC) breakpoint for staphylococci and streptococci for at least 8 hr; the MIC breakpoint for enterobacteria and enterococci was never attained.

Pharmacokinetics of amoxycillin and the rate of depletion of its residues in pigs

Six pigs were used in a two-period crossover study to investigate the pharmacokinetics of amoxycillin after single intravenous and oral doses of 20 mg/kg bodyweight. Twelve pigs were used to study the residues of the drug in muscle, kidney, liver and fat after they had received daily oral doses of 20 mg/kg amoxycillin for five days. The mean (sd) elimination half life (t1/2beta) and mean residence time of amoxycillin in plasma were 3.38 (0.30) and 3.54 (0.43) hours, respectively, after intravenous administration and 4.13 (0.50) and 4.47 (0.30) hours, respectively, after oral administration. After oral administration, the maximum plasma concentration (Cmax) was 7.37 (0.42) microg/ml and it was reached after 0.97 (0.29) hours. Six days after the last oral dose, the mean concentration of amoxycillin in the pigs' kidneys was 21.38 ng/g and in the liver it was 12.32 ng/g, but no amoxycillin could be detected in fat or muscle; the concentrations of amoxycillin in edible tissues were less than the European Union maximal residue limit of 50 microg/kg.

Antimicrobial use in the treatment of calf diarrhea

Calves with diarrhea often have small intestinal overgrowth with Escherichia coli bacteria, regardless of the inciting cause for the diarrhea, and 30% of systemically ill calves with diarrhea have bacteremia, predominantly because of E coli. Antimicrobial treatment of diarrheic calves should therefore be focused against E coli in the small intestine and blood, the 2 sites of infection. Fecal bacterial culture and antimicrobial susceptibility testing is not recommended in calves with diarrhea because fecal bacterial populations do not accurately reflect small intestinal or blood bacterial populations and because the break points for susceptibility test results have not been validated. Antimicrobial efficacy is therefore best evaluated by the clinical response of a number of calves to treatment, with calves randomly assigned to treatment groups. Amoxicillin, chlortetracycline, neomycin, oxytetracycline, streptomycin, sulfachloropyridazine, sulfamethazine, and tetracycline administered PO are currently labeled in the United States for the treatment of calf diarrhea. On the basis of published evidence for the oral administration of these antimicrobial agents, only amoxicillin can be recommended for the treatment of diarrhea. Dosage recommendations are amoxicillin trihydrate (10 mg/kg PO q12h) or amoxicillin trihydrate‐clavulanate potassium (12.5 mg combined drug/kg PO q12h) for at least 3 days; the latter constitutes extra‐label drug use. Parenteral administration of broad‐spectrum β‐lactam antimicrobials–eftiofur (2.2mg/kg IM orSCq12h) and amoxicillin or ampicillin (10 mg/kg IM q12h)–rpotentiatedsulfonamides(25 mg/kg IV or IM q24h) is recommended for treating calves with diarrhea and systemic illness; both constitute extra‐label drug use. In calves with diarrhea and no systemic illness (normal appetite for milk, no fever), it is recommended that the health of the calf be monitored and that oral or parenteral antimicrobials not be administered.

Feasibility of interspecies extrapolation in determining the bioequivalence of animal products intended for intramuscular administration

To examine the validity of extrapolating parenteral product bioequivalence determinations across target animal species, the relative bioavailability of two injectable formulations of ampicillin trihydrate (PolyflexR, a water-based suspension, and Ampi-kel 10R, an oil-based suspension) was examined in calves, sheep and swine. Employing products recognized to be bioinequivalent provided an opportunity to explore potential species-by-formulation interactions. As compared with PolyflexR, Ampi-kel 10R exhibited lower area under the curve (AUC) estimates but higher peak concentrations in all target animal species. Nevertheless, marked interspecies differences were noted in the width and bounds of the confidence intervals about the differences in treatment means. Potential physiological and physico-chemical reasons for these findings are discussed.

Trends in veterinary clinical and fundamental pharmacology: past and future in The Netherlands

Veterinary pharmacology has undergone a gradual development in the Netherlands during this century. Starting from a historical perspective the paper aims to provide an overview of future trends and important issues in the area of veterinary pharmacology and toxicology. It is pointed out that this discipline comprises several subdisciplines as the comparative aspect of both, pharmacology and toxicology, is inherent to veterinary medicine which has to address a broad variety of animal species. Thus, the comparison of drug effects, side effects, and drug disposition as well as the comparison of the species-specific susceptibility to xenobiotics are obvious challenges in this discipline. Several areas in clinical pharmacology are highlighted to indicate future research needs. Finally, the principles of Good Veterinary Practice are presented as the 'golden standard' in veterinary clinical pharmacology.

Pharmacokinetics of amoxicillin/clavulanic acid combination after intravenous and intramuscular administration to pigeons

The pharmacokinetics of amoxicillin/clavulanic acid (4:1) combination were studied after intravenous and intramuscular administration of single doses (25 mg kg(-1) bodyweight) to 50 pigeons. The plasma concentrations-time data were analysed by compartmental pharmacokinetics and non-compartmental methods. The disposition curves for both drugs after intravenous administration were best described by a two-compartment open model. The apparent volumes of distribution of amoxicillin and clavulanic acid were 1.77 litres kg(-1) and 1.30 litres kg(-1) respectively. The body clearances of amoxicillin and clavulanic acid were not significantly different. The elimination half-lives of amoxicillin after intravenous and intramuscular administration were 1.22 (0.09) hour and 1.52 (0.09) hour respectively, and those of clavulanic acid were 1.15 (0.08) hour and 1.49 (0.08) hour. After intramuscular administration both drugs had a significantly longer half-life (P<0.05) than that after the intravenous treatment. The bioavailability after the intramuscular injection was high and similar for both drugs (75.98 per cent for amoxicillin and 74.61 per cent for clavulanic acid). The mean peak plasma concentration of clavulanic acid (0.29 hour) was reached earlier than amoxicillin (0.38 hour) and peak concentrations were proportional to the dose of both products administered (5.81 mg litre(-1) of amoxicillin and 1.89 mg litre(-1) of clavulanic acid). From a single administration it is proposed that an intramuscular dosage regimen of 105 mg kg(-1) of the combination (84 mg kg(-1) of amoxicillin and 21 mg kg(-1) of clavulanic acid) every 12 hours will achieve minimum concentrations > or =0.5 mg litre(-1) (minimum inhibitory concentration of most susceptible pathogens).

Penetration of amoxycillin into the respiratory tract tissues and secretions in pigs

The pharmacokinetic properties of amoxycillin, and its penetration into respiratory tract tissues (alveolar macrophages, bronchial secretions, bronchial mucosa, lung tissue and lymph nodes), were determined in 20 healthy female pigs weighing 29 to 55 kg, after a single intravenous dose of 8.6 mg kg(-1) bodyweight. Following intravenous administration the plasma concentration-time curves were best described by a three-compartment open model. The elimination half-life and the mean residence time were 2.5 and 1.4 hours, respectively. The volume of distribution at steady state was 0.52 litres kg(-1), and the body clearance was 0.40 litres hour(-1) kg(-1). In all structures (except alveolar macrophages) amoxycillin concentration peaked at the first sampling point, one hour after drug administration. The tissue to plasma ratio (based on AUC values) were 0.33 for bronchial secretions, 0.37 for bronchial mucosa, 0.39 for lung tissue and 0.68 for lymph nodes. Traces of amoxycillin were found in alveolar macrophages, but the concentrations were below the limit of quantification. The concentration of amoxycillin in secretions and tissue decreased by a slower rate than the concentration in plasma, resulting in increasing secretion- and tissue-to-plasma concentration ratios.

Bioavailability of amoxycillin in pigs

Amoxycillin was administered to pigs intravenously (i.v.), intramuscularly (i.m.) and orally (p.o.), in a cross-over design to examine the bioavailability (F) of various drug formulations. These included: a sodium salt for reconstitution in water and administration i.v.; trihydrate salt in an oil base for intramuscular administration producing 'conventional' duration of plasma concentrations; a trihydrate salt in oil base giving prolonged (LA) duration, and a trihydrate powder for oral administration in solution. The concentration of amoxycillin in plasma was measured by high-performance liquid chromatography, and its pharmacokinetic variables were assessed for the individual pigs by use of noncompartmental methods. Following i.v. administration (8.6 mg/kg), amoxycillin was eliminated rapidly with a mean residence time (MRT) of 1.4 h. After i.m. administration of the conventional formulation (14.7 mg/kg), the plasma amoxycillin concentration peaked at 2 h at 5.1 micrograms/mL. The bioavailability was 0.83. Intramuscular administration (14.1 mg/kg) of the long acting formulation (i.m. LA), lead to two peaks in plasma at 1.3 and 6.6 h. The bioavailability was calculated to be 1.11. After p.o. administration to fasted pigs, peak concentration was reached after 1.9 h, and the bioavailability was 0.33. In fed pigs, the corresponding values were 3.6 h and 0.28. Data showed that treatment of respiratory tract diseases in pigs by p.o. dosing alone, may not be optimal, because of the relatively low bioavailability and the fact that infections often result in reduced feed and water consumption. A rational treatment regime for susceptible respiratory pathogens includes an initial i.m. injection, followed by p.o. dosing every 12 h. Alternatively, the long acting formulation may be administered i.m. in a dose of 15 mg/kg, which would lead to active plasma concentrations for approximately 48 h.

Pharmacokinetics of amoxicillin/clavulanic acid combination and of both drugs alone after intravenous administration to goats

The pharmacokinetic behaviour of an amoxicillin/clavulanic acid combination (25 mg kg-1), and both drugs alone (amoxicillin 20 mg kg-1), clavulanic acid 5 mg kg-1), was studied after intravenous (i.v.) administration of single doses of 10 goats. The objective was to determine whether there were differences in the plasma kinetics of these drugs when administered in combination or alone. The plasma concentration-time data were analysed by compartmental pharmacokinetics and non-compartmental methods. The disposition curves for both drugs alone and in combination were best described by a biexponential equation (two-compartment open model). The elimination half-lives of amoxicillin were 1.05 +/- 0.09 h alone and 1.13 +/- 0.19 h in combination, and those of clavulanic acid were 0.87 +/- 0.07 h and 0.85 +/- 0.09 h, respectively. The apparent volumes of distribution of amoxicillin and clavulanic acid were similar in the two treatments. Body clearances of amoxicillin were 0.12 +/- 0.01 l h-1.kg alone and 0.11 +/- 0.01 l h-1.kg in combination, and of clavulanic acid were 0.12 +/- 0.02 l h-1.kg alone and 0.12 +/- 0.01 l h-1.kg in combination with amoxicillin. The half-lives and body clearances of amoxicillin and clavulanic acid did not differ significantly when administered alone and in combination. It was concluded that the i.v. administration of amoxicillin and clavulanic acid as a combination product did not alter the disposition kinetics of either drug.

Depletion of the residues of colistin and amoxicillin in turkeys following simultaneous subcutaneous administration

The tissue distribution and depletion of colistin and amoxicillin were studied in 84 turkeys dosed subcutaneously on 4 consecutive days with a formulation containing the two drugs at 0.2 ml/kg per day, corresponding to 50 000 IU of colistin sulphate/kg and 20 mg of amoxicillin trihydrate/kg. All the turkeys were killed 1-30 days after the final dose and samples of muscle, liver, kidney and cutaneous-subcutaneous tissues and of the injection site were taken for analysis for colistin and amoxicillin residues. The colistin concentrations in the liver (117.5 +/- 26.0 ng/g) and cutaneous-subcutaneous tissue (100.0 +/- 35.6 ng/g) were higher than those in kidney (92.0 +/- 34.4 ng/g) or muscle (67.5 +/- 16.9 ng/g) 1 day after the final dose. The concentration of this drug then increased for 9-14 days, followed by a slow decrease. The antibiotic was still present at low concentrations in the kidneys of all the treated birds and in the livers of two turkeys 30 days after the end of treatment. Amoxicillin concentrations were greatest in muscle (389.2 +/- 195.0 ng/g) and at the injection sites (440.3 +/- 213.9 ng/g) 1 day after treatment ceased, with a subsequent rapid decline. This drug was undetectable in the livers and kidneys by 10 days after dosing ceased.

Influence of injection site on the absorption of benzylpenicillin sodium in the dromedary

Benzylpenicillin absorption was compared in four dromedaries following injection subcutaneously and at three different intramuscular sites (neck, semitendinous and gluteal muscles). The rate of absorption (t1/2ab and Tmax) was slower after subcutaneous compared to intramuscular injection, but the extent of absorption (AUC) was similar for both routes of administration. Following intramuscular injection, the data suggest that the extent of absorption was highest from the semitendinous site and lowest in the neck site. These results were discussed and compared to those reported in other species.

Comparative pharmacokinetics of amoxicillin/clavulanic acid combination after intravenous administration to sheep and goats

The pharmacokinetic behaviour of an amoxicillin/clavulanic acid combination was studied after intravenous administration of single doses (20 mg/kg per kg body weight) to five sheep and six goats. The objective was to determine whether there are differences between sheep and goats in the disposition of amoxicillin and clavulanic acid. The plasma concentration-time data were analysed by compartmental pharmacokinetic and non-compartmental methods. The disposition curves for both drugs were best described by a biexponential equation (two-compartment open model) in sheep and goats. The elimination half-lives of amoxicillin were 1.43 +/- 0.16 h in sheep and 1.13 +/- 0.19 h in goats, and of clavulanic acid were 1.16 +/- 0.01 h and 0.85 +/- 0.09 h in sheep and goats respectively. The apparent volumes of distribution of amoxicillin and clavulanic acid were similar in the two species. Body clearances of amoxicillin were 0.09 +/- 0.01 L/h kg in sheep and 0.11 +/- 0.01 L/h kg in goats, and of clavulanic acid were 0.07 +/- 0.01 L/h kg and 0.12 +/- 0.01 L/h kg in sheep and goats respectively. The half-lives and body clearances of amoxicillin and clavulanic acid differed significantly between sheep and goats. It was concluded that the disposition of amoxicillin and clavulanic acid administered intravenously as an amoxicillin/clavulanic acid combination to sheep and goats differed between the two ruminant species. Even though the differences in disposition kinetics of both drugs were statistically significant, the same intravenous dosing rate of this antimicrobial combination can generally be used in sheep and goats.

A study of the disposition of procaine penicillin G in feedlot steers following intramuscular and subcutaneous injection

The disposition of an aqueous suspension of procaine penicillin G (300,000 U/mL) was studied in feedlot steers. Four groups of three steers were used. Steers in groups 1 and 2 received procaine penicillin G once daily for 5 days intramuscularly (i.m.) at a dose of 24,000 U/kg (group 1) or of 66,000 U/kg (group 2). The injection on the last day was administered in the gluteal muscle. Steers in group 3 (i.m. neck injection) and group 4 [subcutaneous (s.c.) injection] each received a single dose of procaine penicillin G at a dose of 66,000 U/kg. From every animal, after the last injection in groups 1 and 2 and following the single injection in groups 3 and 4, a series of blood samples was taken at fixed time intervals. The plasma from these samples was analysed for penicillin G by a high performance liquid chromatography (HPLC) assay in order to determine the disposition of penicillin. The maximum plasma concentration (Cmax) and the area under the curve (AUC) were significantly different between groups 1 and 2, but we found no difference in the disappearance rate constant between these two groups. Group 4 single s.c. injections produced a lower mean Cmax (1.85 +/- 0.27 microgram/mL) than the mean Cmax (4.24 +/- 1.08 micrograms/mL) produced in group 3 by i.m. injections into the neck muscle or the mean Cmax (2.63 +/- 0.27 microgram/mL) produced in group 2 by i.m. injections into the gluteal muscle. However the mean Cmax produced by i.m. injections into the neck muscles (group 3) was higher than the mean Cmax produced by i.m. injections into the gluteal muscle (group 2). Additionally, the disappearance t1/2 was longer (18.08 h) in group 4 following the s.c. injection and shorter (8.85 h) in group 3 following the i.m. neck injection, than the t1/2 following administration of the same dose i.m. into the gluteal muscle (15.96 h) in group 2. In this study, when procaine penicillin G was injected into the gluteal muscle, doses of 66,000 U/kg were necessary to produce plasma concentrations that were above a minimum inhibitory concentration (MIC) for penicillin G of 1.0 microgram/mL as compared to doses of 24,000 U/kg.

Chromatographic methods of analysis for penicillins in food-animal tissues and their significance in regulatory programs for residue reduction and avoidance

Chromatographic methods for penicillin analysis in animal tissues play a significant role in the regulation of the use of these drugs in livestock production. Regulatory agencies rely on data generated from these methods to establish withdrawal times and to determine whether presumptive positive tissue samples from slaughtered animals intended for human consumption contain violative levels of penicillins to necessitate regulatory action. The need to develop sensitive, accurate, and reliable methods to support regulatory programs is examined together with emerging techniques that could be taken advantage of to improve the sensitivity and usefulness of current chromatographic methods for tomorrow's regulatory agency.

Interspecies variations in plasma half-life of ampicillin, amoxycillin, sulphadimidine and sulphacetamide related to variations in body mass

The relationships between the half-lives during the elimination phase (t1/2 minutes) of ampicillin, amoxycillin, sulphadimidine and sulphacetamide and body mass (W, kg) between species of mammals and birds were examined using data from the authors' experiments and collected from the literature. Linear regression of the log half-lives of ampicillin, amoxycillin and sulphadimidine following intravenous injection on the log body mass for a variety of species of mammals and birds revealed significant correlations (r = 0.7709, n = 8, r = 0.7712, n = 8, r = 0.7749, n = 10). The interspecies relationships were described by the allometric equations t1/2 = 31.3 W0.16, t1/2 = 32.7 W0.12 and t1/2 = 129.2 W0.28, respectively. These equations may be of value for estimating dose intervals in species for which no relevant pharmacokinetic data are available.

Comparative pharmacokinetics of amoxicillin administered intravenously to sheep and goats

The pharmacokinetic behavior of sodium amoxicillin was studied after intravenous administration to six sheep and five goats to determine if there are species differences in disposition. The plasma drug concentrations vs. time following intravenous administration of 10 mg/kg were best described by the biexponential equations Cp = 42.9e-0.077.t + 3.68e-0.0134.t for goats, and Cp = 53.5e-0.06.t + 1.69e-0.015.t for sheep. The terminal disposition half-lives for sheep and goats were 46.3 and 66.9 min respectively and were not significantly different. Amoxicillin clearance for sheep and goats were 10.1 and 11.4 ml/min.kg respectively. There were no significant differences between any of the pharmacokinetic parameters measured in sheep and goats.

Perioperative antimicrobial considerations for gastrointestinal surgery of cattle

Perioperative use of antimicrobial drugs constitutes extra-label use of those drugs. Principles of therapeutic and prophylactic use of antimicrobial drugs can guide decisions about their perioperative use. Regimens currently suggested are based on those principles, theoretical information, pharmacokinetic and pharmacodynamic data, extrapolation from studies with other species, empirical data, personal bias, and experience. Controlled clinical investigations are necessary to provide objective data from which specific recommendations can be derived.

The influence of the injection site on the bioavailability of ampicillin and amoxycillin in beagles

Influence of the injection site on bioavailability in dogs was investigated for injections with ampicillin anhydrate or amoxycillin trihydrate suspensions. Firstly, pharmacokinetic parameters were calculated after IV administration of the sodium salts. Then the dogs were injected in the neck (SC), in the lateral thorax region (SC), in the back (IM) and in the thigh (IM), respectively. The most obvious depot effect was seen after subcutaneous injection of ampicillin in the thorax region, though bioavailability seemed to be low. No differences were seen between the injection sites with amoxycillin. For ampicillin SC injection in the neck seems most favourable; for amoxycillin SC injection may be preferred because it is less burdening. Serum concentrations with amoxycillin were higher and persisted longer than with ampicillin. Further investigation is necessary to determine whether this also counts for tissues or focus of infection.

Salmonellosis in veal calves. Some therapeutic aspects

The present investigation was undertaken to improve regimens dosage of amoxycillin, chloramphenicol or trimethoprim-sulphadiazine in Salmonella dublin infected veal calves. The pharmacokinetics of these drugs were studied after i.v., oral, and i.m. administration (bioavailability, local irritation at the injection site, volume of distribution, and elimination half life). The most important conclusion was that amoxycillin, chloramphenicol, and trimethoprim were suitable for oral administration to veal calves, although the bioavailability of chloramphenicol and trimethoprim was significantly less when concurrently administered with a milk replacer. In vitro, the antibacterial activities of these drugs were compared. Addition of trimethoprim to sulphadiazine lowered its MIC for S. dublin, but sulphadiazine reduced the killing rate compared to that of trimethoprim alone. In the efficacy studies the activities of several serum enzymes and the plasma concentrations of Fe, Zn, and Cu were measured, but it appeared, that these biochemical parameters were no better than the clinical parameters body temperature and body weight. Using optimal dosage regimens based on MIC values and blood levels, treatment with either of the three drugs was of equal efficacy.

Disposition of anesthetic and anesthetic-related agents in ruminants

Many factors may influence the actions and fates of anesthetic and anesthetic-related agents in ruminant animals. These considerations need to be taken into account when these drugs are employed clinically. Some of the major principles governing the disposition of CNS-active drugs are reviewed, with special emphasis on the uniqueness of ruminant animals. General pharmacokinetic considerations are also covered as a preamble to a commentary on the kinetic characteristics of anesthetic and anesthetic-related agents that are commonly used in domesticated ruminants.

Pharmacokinetics of chloramphenicol in cows after intramuscular application

The concentrations of chloramphenicol and its water-soluble metabolites in the plasma of six clinically healthy heifers were measured at intervals during five days after intramuscular administration of free chloramphenicol (20 mg/kg) in a vehicle containing 40% of an organic solvent. Estimations were carried out by a colorimetric method and by high pressure liquid chromatography (for the very low values beyond the second day). For free chloramphenicol a peak concentration of 1.7 micrograms/ml at 7.3 h after injection was found (MIC: 5 micrograms/ml). Bioavailability was calculated to be 63%. It is shown that absorption was apparently not a uniform process but occurred rather slowly (t 1/2 (ab) = 10.2 h) for the main part of the available dose, whereas one sixth was quickly absorbed (t'1/2 (ab) = 0.7 h). The apparent half-time of elimination was 10.2 h for the unchanged drug. At the fifth day after administration the plasma concentration was below the limit of detectability (10 ng/ml) in all animals.

Effect of injection site on the bioavailability of an oxytetracycline formulation in ruminant calves

The oxytetracycline (OTC) disposition was studied in a group of six calves following the administration of an oxytetracycline-10 per cent formulation (i) intravenously (i.v.), (ii) subcutaneously (s.c.) in the lateral neck, and intramuscularly (i.m.) in (iii) the lateral neck, (iv) the shoulder (M. triceps brachii), and (v) the buttock (M. semitendineus). The dose levels used for the intravenous route and other routes were respectively 17.0 +/- 2.3 and 18.3 +/- 1.25 mg OTC/kg. The peak OTC concentrations (Cmax) were achieved with the s.c. and i.m. routes between 4 and 8 hours after injection, the highest being found after application in the shoulder (Cmax:6.9 +/- 0.82 microgram/ml plasma). The Cmax for the s.c. and other i.m. routes in application was similar to each other, ranging from 5.0 to 5.5 micrograms/ml plasma. For different points in time after injection the partial bioavailability was calculated. At 52 h post injection (p.i.) maximal bioavailability was observed for the i.m. shoulder route, viz. 98.1 +/- 7.0 per cent of the administered dose, while at 76 h p.i. similar bioavailabilities were achieved for the i.m. neck and shoulder route, namely 93.3 +/- 8.9 and 99.4 +/- 4.2 per cent, respectively. The lowest bioavailability (83.1 +/- 13.4 per cent) was obtained following the i.m. buttock route at 76 p.i. An obvious irritating effect was observed after s.c. application in the neck an di.m. injection in the buttock, which had disappeared at 5 days p.i. It is assumed that the longer persistence of OTC in plasma resulting with the latter two routes of administration was due to this irritation effect.

Comparative plasma ampicillin levels and bioavailability of five parenteral ampicillin formulations in ruminant calves

Plasma ampicillin concentrations were determined in an eight-ways crossover trial involving six ruminant calves, which were treated intravenously (i.v.) with sodium ampicillin at 15.5 mg/kg and intramuscularly (i.m.) with five different ampicillin trihydrate or ampicillin anhydrate formulations at 7.7 mg/kg. The mean plasma concentration-time curve (Cp) after intravenous ampicillin sodium administration was described biexponentially, as: Cp = 38.8 e -0.0268t + 0.45 e -0.0058t. Intramuscular injection, into the lateral neck, of Ampikel-20 and Polyflex resulted in 100 per cent bioavailabilities within 12 h post injection (p.i.), but the biological half-lives (t1/2) were different, being 2.1 and 3.8 h, respectively. Ampikel-20 produced the highest peak plasma drug concentrations (mean C max :4.8 microgram ampicillin/ml). After intramuscular injection of Penbritin the mean bioavailability for the first 12 h p.i. was 63 per cent, the mean t1/2 was 5.9 h, and the mean Cmax was 1.8 microgram/ml. Treatment with Albipen and Duphacillin resulted in low plasma ampicillin levels, which were maintained for 3 to 6 days p.i., limited bioavailability during the first 12 h p.i., and a mean t1/2 of 22.2 and 11.9 h, respectively. Plasma concentrations of ampicillin from four hours onwards after i.m. and s.c. administration of Ampikel-20 at a dose level of 15.5 mg/kg were similar. The duration of potentially therapeutic plasma ampicillin concentrations after administration of each formulation is presented. Pre-slaughter withdrawal times for diseased calves are suggested for the different formulations studied.

Pharmacological aspects of chloramphenicol administration by the intramammary route to lactating dairy cows

Concentrations of chloramphenicol (C M) were determined, by microbiological assay, in the milk and blood serum of 17 culled dairy cows after intramammary infusion of an approved parenteral CM product (Gloveticol) and in the milk of 16 lactating cows after treatment with two approved CM products for intramammary infusion, at dosages ranging from 1 to 30 g/cow. C M was quickly absorbed from the udder into the blood circulation; the doses of 12.5 and 25 g/cow were almost completely absorbed within 20 hours. Absorption half-life (t1/2ab) from fully functioning quarters was 57+/-18 minutes, and the t1/2ab from partially functioning quarters was 125+/-37 minutes. Mean peak serum C M concentrations were 6.1, 16.2, and 37.4 microg/ml after the cows had been infused with 5, 12.5, and 25 g, respectively. These values were considerably higher than the corresponding peak serum C M concentrations reported following intramuscular injection of equivalent doses of the drug. C M residues were not detectible microbiologically in milk from treated quarters 20 hours after treatment with 5 g or 6.25 g, and 36 hours after treatment with 15 g. Drug concentrations in the milk from the non-treated quarters were approximately 70 per cent of the corresponding serum drug levels. Serum CM concentrations of potential therapeutic value in the treatment of gram-negative bacterial infections, i.e. > 5 microg/ml, were maintained for 8 hours after cows had been infused with 12.5 g, and for 12 hours after infusion with 25 g. The implications of the improved systemic availability of C M infused by the intramammary route over the intramuscular route are discussed in terms of potential therapeutic efficacy, local irritation, and duration of drug residues.