Determination of paromomycin residues in turkey tissues by liquid chromatography/mass spectrometry.

A liquid chromatography-electrospray-mass spectrometry method has been developed and validated for the determination of paromomycin in turkey muscle, liver and kidney, using kanamycin as internal standard. The method consists of solid-phase extractions on mixed-mode columns. The chromatographic separation was carried out on a C(18) column using binary gradient elution containing acetonitrile and 5mM pentafluoropropionic-acid in water. The method was evaluated for specificity, linearity, recovery, accuracy, limit of detection, limit of quantification, intra- and inter-day repeatability, and stability. It was proven to be selective, linear, precise and accurate over the concentration range tested (0.5xMRL-2xMRL for each tissue) with correlation coefficients >0.990. The method was successfully used for the residue determination of PARO from edible tissues of turkeys.

Pharmacokinetics of clindamycin HCl administered intravenously, intramuscularly and subcutaneously to dogs.

A buffered aqueous solution of clindamycin Hcl (200 mg/mL) was injected intravenously (i.v.) intramuscularly (i.m.) and subcutaneously (s.c.) in a non-randomized, partial cross-over trial involving six male and six female dogs. Blood samples were collected at conventional, predetermined time periods and serum drug concentrations were determined by microbiological assay. Dogs were observed clinically for signs of pain, and activity of serum creatine phosphokinase (CPK) was monitored after i.m. dosing. The i.v. data from five of the dogs best fitted a two-compartment open-system pharmacokinetic model whereas a non-compartment model was most suitable for analysis of the data from the remaining seven dogs. The mean i.v. elimination half-life (t1/2 beta) and the mean residence time (MRT) were 124 and 143 min, respectively. The mean volume of distribution at steady state (Vss) was 0.86 L/kg. Little pain was recorded upon i.m. injection; mean peak serum drug concentration (Cmax) was 4.4 micrograms/mL, the elimination half-life (t1/2el) was 247 min and the calculated bioavailability (F) was 115% of the i.v. dose. Serum CPK activity was elevated to 25-fold the pretreatment level in samples collected 4, 8 and 12 h after i.m. injection. Pain was not recorded after s.c. drug administration; the mean Cmax of 20.8 micrograms/mL was significantly greater than the corresponding value for the i.m. route, and F was 310%. The s.c. route appears to be superior to the i.m. route in terms of local tolerance and serum drug level; a 10 mg/kg SID treatment regimen is suggested for treatment of canine infections due to clindamycin sensitive bacteria.

Pharmacokinetics and penetration of danofloxacin from the blood into the milk of cows.

The single-dose disposition kinetics of danofloxacin were determined in clinically normal lactating cows after intravenous (i.v.) and intramuscular (i.m.) administration of the drug at 1.25 mg/kg. The drug concentrations in blood serum and milk were determined by microbiological assay methods and the data were subjected to kinetic analysis. The mean i.v. and i.m. elimination half-lives (t1/2el) in serum were 54.9 and 135.7 min, respectively. The steady-state volume of distribution (Vss) was 2.04 L/kg. The drug was quickly absorbed after i.m. injection but a 'flip flop' effect was clearly evident and bioavailability was > 100%. Penetration of danofloxacin from blood into milk was rapid and extensive with drug concentrations in milk exceeding those in serum beginning 90-120 min after i.v. and i.m. administration and onwards. Milk danofloxacin concentrations equal to or higher than the minimal inhibitory concentrations (MIC) for pathogenic Gram-negative bacteria and Mycoplasma species were maintained over approximately 24 h. Concentrations greater than the MIC for Staphylococcus aureus were maintained in the milk for 12 h.

Combined effect of ampicillin, colistin and dexamethasone administered intramuscularly to dairy cows on the clinico-pathological course of E. coli-endotoxin mastitis.

The effects of a single intramuscular injection of a drug product containing ampicillin, colistin and dexamethasone, as a suspension in a diester of propylene glycol of medium-chain fatty acids, on the clinico-pathological course of experimental Escherichia coli-endotoxin mastitis was examined in 30 dairy cows. Cows were divided into five groups, six cows per group, and 24 of them were infused with E. coli endotoxin into two quarters of their udders. The drug product was injected at 25,000 IU colistin sulphate, 10.0 mg ampicillin anhydrate and 0.025 mg dexamethasone acetate.kg-1 body weight as follows: Group 2 cows, immediately post-endotoxin infusion (PEI); Group 3 cows, 2 h PEI and, Group 4 cows, 4 h PEI. Group 1 cows were not treated with the product and served as a positive (endotoxin only) control while Group 5 cows were not challenged with endotoxin and were not treated with the product. A clinical mastitis score (CMS) was developed to quantitatively assess the degree of inflammation. Blood biochemistry and hematological parameters were used to monitor the immediate effects of treatment on several conventional inflammatory markers. Milk somatic cell counts (MSCC), milk electrical conductivity and daily milk production were among the parameters used to monitor systemic and local inflammatory reactions. Administration of the drug product immediately PEI and 2 h PEI clearly nullified some of the most severe early systemic reactions to inflammation but the effect of therapy on the local inflammatory markers was not as obvious. Notewhorthy, however, were the effects of the treatment on reducing the duration of elevated quarter MSCC and the increase in the speed of return to pre-endotoxin challenge daily milk production levels.

Pharmacokinetics and penetration of marbofloxacin from blood into the milk of cows and ewes.

The single-dose disposition kinetics of marbofloxacin were determined in lactating cows and ewes after intravenous (i.v.) and intramuscular (i.m.) administration of 2, 2.5 and 4 mg/kg. Drug concentrations in blood and milk were determined by microbiological assay and the data were subjected to compartmental and non-compartmental kinetic analyses. In cows, the i.v. serum elimination half-life (t1/2 beta) was approximately 2 h and the i.m. serum elimination half-life (t1/2el) was approximately 3 h. The mean steady-state volume of distribution (Vss) was 1.5 l/kg for the cows and 0.6 l/kg for the ewes. The i.m. availability was nearly 100% for both cows and ewes. Drug penetration into the milk was rapid and extensive with milk marbofloxacin concentrations exceeding those in serum 2 h after administration. Milk drug concentrations equal to or greater than the minimal inhibitory concentrations for the majority of gram-negative udder pathogens were maintained for approximately 12 h after i.v. and i.m. treatment of 2-4 mg/kg. The drug was not detected in milk 24 h after treatment (sensitivity limit of assay = 0.05 microgram/ml).

Pharmacokinetics and penetration of danofloxacin from the blood into the milk of ewes.

The single-dose disposition kinetics of danofloxacin were determined in clinically normal, lactating ewes after intravenous (i.v.) and intramuscular (i.m.) administration of 1.25 mg/kg. The drug concentration in the blood serum and milk were determined by microbiological assay and the data were subjected to compartmental and non-compartmental kinetic analyses. The i.v. and im elimination half-lives in serum (t1/2 beta and t1/2el) were 125.0 +/- 38.6 min and 209.4 +/- 56.3 min, respectively. The steady-state volume of distribution (Vss) was 1.9 +/- 0.7 L/kg. The drug was quickly absorbed after the i.m. injection and the i.m. availability was 100%. Penetration of danofloxacin from the blood into the milk was rapid and extensive with drug concentrations in milk exceeding those in serum beginning 60-90 min after administration and onwards. Milk danofloxacin concentrations equal to or higher than the minimal inhibitory concentrations (MIC) for pathogenic Gram-negative bacteria and Mycoplasma species were maintained over approximately 24 h. Concentrations greater than the MIC for Staphylococcus aureus were maintained in the milk for 12 h.

Tilmicosin antibacterial activity and pharmacokinetics in cows.

The minimal inhibitory concentration (MIC) of tilmicosin for 90% of 112 Staphylococcus aureus isolates from the bovine udder was 0.78 microgram/mL and 149 of 164 (90.8%) other gram-positive udder pathogens were inhibited by tilmicosin concentrations < 3.12 micrograms/mL. The MIC of the drug for 19 of 22 S. aureus isolates was < 0.78 microgram/mL when the test was conducted using Mueller-Hinton (MH) agar or MH agar containing 7.5% skimmed milk. Acute cardiac toxicity followed intravenous (i.v.) injection of the drug at 10 mg/kg to 3 cows, but animals appeared clinically normal within 30 min after treatment. The pharmacokinetics of i.v.-administered tilmicosin is typical for the macrolide class of antibiotics, i.e. low serum drug concentrations and a large volume of distribution (> 2.0 L/kg). The elimination half-life (t1/2 beta) values for 3 cows were 46.4, 56.0 and 72.8 min. The drug was administered subcutaneously (s.c.) to 5 cows at 10 mg/kg; the elimination half-life (t1/2el) was 4.18 +/- 0.55 h and the mean s.c. bioavailability was 22%. Rapid and extensive penetration of tilmicosin from blood into milk, and slow elimination from the milk were among the characteristic kinetic features of the drug after i.v. and s.c. administration. Tilmicosin was injected s.c. at 10 mg/kg once to 9 cows after the last milking of lactation; dry udder secretion samples were collected daily for 11 consecutive days and assayed microbiologically. Concentrations of drug > 0.78 microgram/mL were found in the secretion for 8-9 days after dosing. Systemic side-effects were not observed after s.c. drug administration.

Pharmacokinetics of ampicillin administered intravenously and intraosseously to kittens.

An aqueous solution of ampicillin sodium (100 mg ml-1) was administered intravenously and intraosseously to six kitten at 50 mg kg-1 in a crossover study. Jugular vein blood samples were taken at intervals up to eight hours after treatment and the serum ampicillin concentration-time data, derived from a microbiological assay, were analysed pharmacokinetically. The disposition kinetics of ampicillin administered by the two routes were very similar. The mean elimination half-life (t1/2 beta), the area-derived volume of distribution (Varea) and the total body clearance (ClB) values after the intravenous and intraosseous treatment were 86.3 and 79.0 minutes, 0.9 and 0.8 litre kg-1 and 7.3 and 7.6 ml min-1 kg-1, respectively. No side-effects related to the intraosseous administration of the drug were observed.

Tissue distribution and binding to plasma proteins of norfloxacin nicotinate after intramuscular administration in pigs.

Three clinically normal pigs were given a single intramuscular injection of an aqueous solution of norfloxacin nicotinate (NFN) at 14 mg/kg body weight. Animals were killed 4 h after treatment and the concentrations of norfloxacin in various biological fluids and tissues were determined by chemical (high performance liquid chromatography, HPLC) and microbiological assay methods. Drug distribution throughout the body was presented as actual concentrations (micrograms/ml and ppm) in each sample and as the ratio of drug concentration in tissue to drug concentration in plasma. Highest concentrations were found in the urine, kidney, liver and bile. The drug was not detected in ocular fluid, brain tissue (by microbiological assay), fat (by HPLC) and skin (by HPLC). Tissue-to-plasma concentrations ratios were near to, or greater than, 1.0 (HPLC assay) for the kidney, liver, spleen, muscle, lung, adrenals, salivary glands, pleural and synovial fluid, and smaller than 1.0 for cerebrospinal fluid, brain tissue and lymph nodes. Agreement between the chemical and microbiological assay results was variable, depending on the type of tissue and biological fluid tested. Binding of norfloxacin to plasma proteins in pig is low (23%-29%). The distribution pattern of the drug in pig, laboratory animals and humans is very similar; it can be characterized as extensive, with tissue-to-serum ratios reaching 2:1 or more in certain non-excretory organs. These values may reflect intracellular concentrations of the drug.

Clinical pharmacokinetic characterization of norfloxacin nicotinate in swine following systemic administration.

Norfloxacin nicotinate (NFN) is a new water-soluble fluoroquinolone antibacterial agent. The in vitro activity of NFN for microorganisms isolated from swine and the pharmacokinetic properties of NFN following single intravenous (i.v.), intramuscular (i.m.) and subcutaneous (s.c.) administration were investigated. The minimal inhibitory concentrations (MIC's) of NFN for a wide range of reference (ATCC-American Type Culture Collection) microbial swine isolates, comprising 21 bacterial and 5 mycoplasmal species, ranged between 0.03 micrograms/ml (for Salmonella cholerasuis and Actinobacillus pleuropneumonia) and 12.5 micrograms/ml (for Streptococcus porcinus). The MIC of NFN for Mycoplasma hyopneumoniae, the causative agent of enzootic pneumonia of pigs, was < 1.0 microgram/ml although M. hyosynoviae was less sensitive, with a MIC value of 3.12 micrograms/ml. The MIC values of the drug for swine field isolates, comprising 8 bacterial species, were in good agreement with the values determined for the corresponding ATCC strains. Pharmacokinetic values for NFN were calculated following i. v. administration at 7.0 mg/kg and i. m. and s. c. administration at 14.0 mg/kg in a 3-way cross over study involving 6 pigs. Plasma concentrations of unchanged drug were determined by HPLC during 24 h post injection. Plasma NFN concentrations measured after i.v. dosing best fitted a 2-compartment open system pharmacokinetic model. The harmonic mean distribution half-life (t1/2 alpha) and elimination half-life (t1/2 beta) were 4.2 minutes and 2.1 h, respectively. The mean residence time (MRT) was 2.9 +/- 0.6 h and the steady state volume of distribution (Vss) was 3.2 +/- 0.1 l/kg. The mean t1/2 beta values after either i. m. or s. c. administration were 4.45 h with very rapid absorption rates (< 15 min to peak plasma drug concentration). Bioavailability was 51-64%. Less than 20% and 25% of the dose were excreted in the urine as parent drug during the first 24 h after i.v. and s.c. dosing, respectively whereas the amount of unchanged drug recovered in the feces was very small (1.3 to 1.6% of the dose). The pharmacokinetic and MIC data generated in the course of the present study suggest that a dose schedule of 14.0 mg/kg injected i. m. or s. c. every 24 h is capable of achieving and maintaining tissue drug concentrations of potential therapeutic value for the treatment of the most common bacterial and mycoplasmal infections in swine.