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Biomedical subjects

G E Burrows

Publications and source records attributed to G E Burrows.

At least 37 records · Page 2Linked to original sources
PubMed1992

Pharmacokinetics of intravenously and orally administered pyrimethamine in horses.

Single-dose pharmacokinetic variables of pyrimethamine were studied in horses. Pyrimethamine (1 mg/kg of body weight) was administered IV and orally to 6 adult horses, and plasma samples were obtained at frequent intervals thereafter. Plasma pyrimethamine concentration was assayed by gas chromatography, and concentration-time data were analyzed, using a pharmacokinetic computer program. The IV and oral administration data were best described by 3-compartment and 1-compartment models, respectively. The median volume of distribution at steady state after IV administration was 1,521 ml/kg and the median elimination half-time was 12.06 hours. Mean plasma concentration after oral administration fluctuated between a maximal concentration of 0.18 microgram/ml and 0.09 microgram/ml (24 hours after dosing). Bioavailability after oral administration was 56%.

Administration, Oral↗
PubMed1992

Pharmacokinetics, penetration into cerebrospinal fluid, and hematologic effects after multiple oral administrations of pyrimethamine to horses.

Pharmacokinetics, CSF penetration, and hematologic effects of oral administration of pyrimethamine were studied after multiple dosing. Pyrimethamine (1 mg/kg of body weight) was administered orally once a day for 10 days to 5 adult horses, and blood samples were collected frequently after the first, fifth, and tenth doses. The CSF samples were obtained by cisternal puncture 4 to 6 hours after administration of the first, third, seventh, and tenth doses. Pyrimethamine concentration in plasma and CSF was quantified by gas chromatography, and plasma concentration-time data were analyzed, using a pharmacokinetic computer program. Repeated daily dosing resulted in accumulation of pyrimethamine in plasma, with steady state being achieved within 5 days, when the mean peak plasma concentration was more than twice that measured after the first dose. Pyrimethamine concentration in CSF was 25 to 50% of corresponding plasma concentration and did not appear to accumulate with successive administration of doses. Blood samples collected during and after the dosing regimen were submitted for hematologic analysis; neutrophil numbers decreased slightly, but remained within normal range for adult horses.

Administration, Oral↗
PubMed1992

Response of Pasteurella haemolytica to erythromycin and dexamethasone in calves with established infection.

A subcutaneous soft tissue infection model in calves was used to study the in vivo response of Pasteurella haemolytica to erythromycin and dexamethasone. Two tissue chambers were implanted SC in each of 12 calves. At 45 days after implantation, all tissue chambers were inoculated with an erythromycin-sensitive strain of P haemolytica. Starting 24 hours after inoculation, calves were allotted to 4 groups of equal size and a 2 x 2-factorial arrangement of treatments was applied: 3 calves were given erythromycin (30 mg/kg of body weight, IM, for 5 days), 3 calves were given dexamethasone (0.05 mg/kg, IM, for 2 days), 3 calves were given erythromycin and dexamethasone, and the remaining calves served as nontreated controls. Chamber fluids were tested daily, and the response to treatment was measured. Neither erythromycin nor dexamethasone affected viability or growth of bacteria within tissue chambers. Dexamethasone had no effect on the influx of neutrophils into infected chambers. Despite repeated administration of a high dose of erythromycin and attainment of adequate concentration in serum, erythromycin concentration in chamber fluids did not exceed the minimal inhibitory concentration established in vitro. These results indicate that the clinical efficacy of erythromycin against P haemolytica sequestered in consolidated pneumonic lesions may not be well correlated with predictions based on serum pharmacokinetic and in vitro susceptibility data.

Albumins↗
PubMed1991

Therapy of bovine bacterial pneumonia.

Practical strategies for developing rational therapeutic regimens based on in vitro sensitivity and pharmacokinetic disposition are presented. Special attention is given to Pasteurella haemolytica, which is regarded as the most frequent cause of bovine bacterial pneumonia. Bacterial-dependent and host-dependent causes of therapeutic failure and potentially valuable novel therapies and drug combinations are considered.

Animals↗
PubMed1990

Acute oxalate poisoning attributable to ingestion of curly dock (Rumex crispus) in sheep.

Ten of 100 mature ewes were afflicted with acute oxalate toxicosis within 40 hours after being temporarily penned in a lot that contained considerable growing Rumex crispus (curly dock). Clinical signs of toxicosis included excess salivation, tremors, ataxia, and recumbency. Affected ewes were markedly hypocalcemic and azotemic. Oxalate crystals were not observed in urine. Gross postmortem lesions were minimal and nondiagnostic in 2 ewes that died peracutely, but perirenal edema and renal tubular degeneration were clearly observable in ewes euthanatized on the third day of toxicosis. Diagnosis of oxalate toxicosis was confirmed by histopathologic findings. Samples of Rumex spp contained 6.6 to 11.1% oxalic acid on a dry-weight basis, a concentration comparable with that in other oxalate-containing plants that have caused acute oxalate toxicosis.

Acute Kidney Injury↗
PubMed1989

Plants causing sudden death in livestock.

A number of plants are capable of producing intoxication of sufficient severity as to cause death within 12 hours of the onset of clinical signs. Those most rapid in their lethal effects are the cyanogenic plants and yew. Nitrate-accumulating plants likewise are capable of causing sudden death with only a brief appearance of signs. Most toxic plants, however, typically either require a longer time for the intoxication to develop and become lethal or sudden death is the exception rather than the rule following ingestion. In these cases, diagnosis of the problem may be facilitated by recognition of arrays of clinical signs that appear. Seven major groups of presenting signs can be distinguished: dyspnea and polypnea, hemorrhage, prominent excessive muscular activity, depression and/or weakness, diarrhea and weakness, excessive salivation and/or regurgitation and/or colic, and weakness and incoordination and/or tremors. Based on these and accompanying signs in surviving animals, many of the causes of sudden death can be differentiated. In addition, pathological changes visible on necropsy and identification of plant fragments in the rumen and stomach may be of diagnostic value.

Animals↗
PubMed1989

A comparison of the various routes of administration of erythromycin in cattle.

A comparison of i.v., i.m. and s.c. administration erythromycin base in polyethylene glycol at 15 mg/kg and 30 mg/kg body weight was carried out in beef-type calves of approximately 200 kg body weight. Additional evaluations were carried out with oral administration of erythromycin phosphate and erythromycin stearate. Absorption of erythromycin was very slow by both the i.m. and s.c. routes of administration with a Kab of 0.0135 min-1 and 0.0185 min-1 for i.m. and 0.0032 min-1 and 0.0074 min-1 for s.c. at 15 mg/kg and 30 mg/kg, respectively. The bioavailability (32-42%) and peak serum concentrations were much lower with s.c. than with i.m. (60-65%) administration. The disposition of erythromycin administered i.v. appeared to be representative of dose-dependent kinetics rather than dose-independent first-order kinetics inasmuch as the elimination half-time (t1/2B) increased from 174.5 +/- 13 min for the 15 mg/kg dosage to 239 +/- 10.8 min with 30 mg/kg dosage. An acute apparent cardiovascular effect accompanied i.v. administration of erythromycin at 30 mg/kg dosage but not at 15 mg/kg. Severe diarrhea followed oral administration of either erythromycin phosphate or erythromycin stearate.

Absorption↗
PubMed1989

Interactions between chloramphenicol, acepromazine, phenylbutazone, rifampin and thiamylal in the horse.

The potential for interactions between chloramphenicol, phenylbutazone, acepromazine and thiamylal and chloramphenicol, rifampin, and phenylbutazone were evaluated in two groups of experiments. In the first, five horses were given thiamylal intravenously (iv) (6.6 mg/kg) after pretreatment with acepromazine, and the time of recumbency was determined. Administration of chloramphenicol iv (25 mg/kg) 1 h prior to anaesthesia significantly lengthened the recumbency time from 21.8 +/- 4.8 mins to 36.0 +/- 8.3 mins. There was an apparent but not statistically significant decrease in recumbency time when phenylbutazone (4.4 mg/kg) was administered iv daily for 4 days prior to anaesthesia. In the second series of experiments, phenylbutazone (4.4 mg/kg), chloramphenicol (25 mg/kg) and rifampin (10 mg/kg) were administered in various sequences to five different horses. Chloramphenicol pretreatment produced a significant decrease in the elimination rate and rifampin a significant increase in the elimination rate of phenylbutazone. The half-life of elimination of phenylbutazone alone was about 4 h. Following four days pretreatment with rifampin it was approximately 2.7 h, it was approximately 5.6 h and 9.5 h, respectively, when chloramphenicol was administered in one dose 1 h before or two doses 12 h and 1 h before phenylbutazone.

Acepromazine↗
PubMed1989

In vitro assessment of the efficacy of erythromycin in combination with oxytetracycline or spectinomycin against Pasteurella haemolytica.

The effects of combining erythromycin (Ery) with oxytetracycline (Oxy) or spectinomycin (Sp) on Pasteurella haemolytica were evaluated in vitro using the chessboard (checkerboard) technique. These combinations were selected because all are drugs widely used in bovine respiratory disease treatment, and they represent possible sequential or complementary mechanisms of action. Using the recommended breakpoints of greater than 4 micrograms/ml for Ery, 16 micrograms/ml for Oxy, and 32 micrograms/ml for Sp, of the 33 P. haemolytica isolates, 32 were resistant to Oxy, 27 to Sp, and 14 to Ery. Based on the fractional inhibitory concentration index, Ery and Oxy in combination were synergistic or additive against 32 of 33 isolates. The combination of Ery and Sp was synergistic or additive against 27 of 33 isolates. No instances of antagonism were seen. When the effects were considered within the context of therapeutically achievable serum/tissue concentrations, the effects of Ery and Oxy in combination were only marginal. Thus, against P. haemolytica isolates, Ery and Sp appeared to represent an effective antimicrobial combination, whereas Ery and Oxy were only of marginal efficacy as a combination.

Animals↗
PubMed1989

Serum and tissue concentrations of erythromycin in calves with induced pneumonic pasteurellosis.

The effects of pneumonia on the pharmacokinetics of erythromycin administered IM and the tissue concentration changes with time were evaluated in 2-month-old calves. Pneumonia was induced by injection of Pasteurella haemolytica cultures through the thoracic wall into each lung. Six days prior to induction of pneumonia, erythromycin (15 mg/kg) was administered in a single IM dose. Erythromycin was administered again 48, 72, and 96 hours after injection of P haemolytica. On the third day of erythromycin administration (96 hours), the calves were serially euthanatized in groups of 4 calves each at 2, 5, 8, 12, 18, and 24 hours after the final dose was given. Tissue concentrations of erythromycin in kidney, liver, lung, muscle, CSF, and serum were determined. Neither the serum concentrations nor the overall pharmacokinetic values were significantly (P less than or equal to 0.05) changed by pneumonia. The concentrations of erythromycin were maximal at 5 hours for liver, muscle, and serum and at 8 hours for CSF, kidney, and lung. Serum and muscle concentrations were similar, whereas concentrations in CSF were lower than in serum and higher in kidney, liver, and lung. The lung/serum ratios were approximately 2.5 to 3 at 8 through 24 hours after IM administration. The peak concentration in lung was approximately 6 micrograms/g at 8 hours.

Animals↗
PubMed1989

Hypotension produced by rapid intravenous administration of chloramphenicol in anaesthetised dogs.

Rapid intravenous administration (60 mg s-1) of chloramphenicol (50 mg kg-1) in a 40 per cent w/v polyethylene glycol (400 to 600), 30 per cent ethyl alcohol, 2 per cent benzyl alcohol and 28 per cent distilled water vehicle produced a transient but significant decrease in systemic arterial blood pressure and heart rate with no effect on central venous pressure in sodium pentobarbital anaesthetised dogs. The vehicle alone had no significant effect on any of the parameters studied. Various approaches including the use of anticholinergic, antihistaminergic, antiadrenergic and ganglion blocking drugs failed to attenuate chloramphenicol induced hypotension and bradycardia. However, the hypertensive response to bilateral carotid arterial occlusion was significantly attenuated by rapid intravenous administration of chloramphenicol. The results clearly indicate that chloramphenicol itself, but not its vehicle, is responsible for the severe hypotension and bradycardia. These results also suggest that chloramphenicol-induced hypotension and bradycardia might be mediated peripherally via vasodilation due to its direct effect on vascular smooth muscle and centrally via interruption of the baroreceptor reflex pathway.

Animals↗