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Biomedical subjects

G E Burrows

Publications and source records attributed to G E Burrows.

At least 55 records · Page 3Linked to original sources
PubMed1988

Experimental chloramphenicol intoxication in neonatal calves: intravenous administration.

Chloramphenicol was administered intravenously for eight to 17 days to five newborn calves at a daily dosage of 100 mg kg-1. Haemodynamic, haematological, blood chemistry, serum enzyme, urinalysis and clinical responses were evaluated. High levels of serum chloramphenicol were observed throughout the study although a marked increase in elimination rate was seen with increasing age. The most severe adverse effects were severe hypotension following rapid intravenous administration and severe gastrointestinal dysfunction with diarrhoea accompanying prolonged high dosage. There appeared to have been a haematological effect in one calf, but it was of minor significance compared with the other effects.

Animals↗
PubMed1987

Comparative pharmacokinetics of gentamicin, neomycin and oxytetracycline in newborn calves.

The pharmacokinetics of three antibiotics--gentamicin, neomycin and oxytetracycline were determined in newborn calves. The kinetic determinations, using two-compartment open models, were made at increasing ages from 1 day to 42 days and compared with those made from older calves (250+ days). Although all three antibiotics are eliminated unchanged primarily by glomerular filtration, there were marked differences in the development of elimination processes for individual drugs. The pharmacokinetics of neomycin were not influenced by age. Although the elimination half-life of gentamicin appeared to decrease with age, the changes were not significant and were due to an increased elimination rate in only one calf. There was no change with age in the remaining three calves. Oxytetracycline elimination was significantly reduced in newborn calves. This was exemplified by a decrease in the half-life of elimination t1/2 (beta) from 672.5 +/- 99.4 in the newborn to 385.6 +/- 76.8 at 6 weeks of age, and 377.3 +/- 40.8 min in the 250-day-old calf. These changes were consistent in all four calves. The rate of elimination remained low for the first 4 weeks of life. The volume of distribution Vd, area was not changed after the first week of life. Based on pharmacokinetic changes, an adjustment of dosage is indicated for oxytetracycline in the newborn calf as compared to the older calf or adult.

Age Factors↗
PubMed1987

The prophylactic effect of corn supplementation on experimental nitrate intoxication in cattle.

Sodium nitrate was administered through rumen cannulae to produce NO-3 intoxication in four cows (382 to 445 kg body wt) fed prairie grass hay and a protein-mineral supplement. The cows were fed 0, 1.6 or 3.2 kg of dry rolled corn daily for 10 d prior to sodium nitrate administration. Sodium nitrate administration was followed by a marked increase in intraruminal NO-2 and NH3 and blood NO-2 and methemoglobin. Six of eight cows fed 0 and 1.6 kg of corn were given methylene blue to treat severe methemoglobinemia, while none of the cows fed 3.2 kg corn required such therapy. Feeding of 3.2 kg of corn protected against nitrate poisoning by reducing intraruminal nitrite and blood methemoglobin (P less than .05).

Animal Feed↗
PubMed1986

Chloramphenicol, lincomycin and oxytetracycline disposition in calves with experimental pneumonic pasteurellosis.

The effects of pneumonia on the pharmacokinetics of chloramphenicol, lincomycin, and oxytetracycline were evaluated in two-month-old calves. Pneumonia was induced by injection of Pasteurella haemolytica cultures directly through the thoracic wall into each lung. Six days prior to induction of pneumonia, the antibiotics were administered in a single i.v. dose. The antibiotics were administered again 48 (i.v.), 60 and 72 h (i.m.) following injection of P. haemolytica. The pharmacokinetics of chloramphenicol (25 mg/kg) and lincomycin (10 mg/kg) were not significantly different in calves with pneumonia. The hybrid rate constant beta for oxytetracycline was increased in calves with pneumonia from 0.0034 +/- 0.0003/min to 0.0048 +/- 0.0007/min between 2 h and 8 h. Thus the elimination half-life in serum was shortened from 212.4 +/- 20.3 min to 149.3 +/- 19.5 min. In addition, there was an apparent but not statistically significant decrease in K12 with pneumonia. These findings accentuate the need for observance of 12-h dose intervals with oxytetracycline.

Animals↗
PubMed1986

Antibiotic disposition in experimental pneumonic pasteurellosis: gentamicin and tylosin.

The effects of severe respiratory disease on the disposition of antibiotics were evaluated using two drugs chosen because of their widely differing solubility characteristics. The experiments were carried out in series, using five calves for each drug. The drugs were given to seven week old calves before and after induction of pneumonia by bilateral intrapulmonary administration of 3 mL of 5 X 10(7) colony forming units of Pasteurella haemolytica. Following inoculation, the calves developed clinical signs of pneumonia and were given gentamicin (5 mg/kg) or tylosin (10 mg/kg) 48, 60 and 72 hours after Pasteurella administration. There was a statistically significant decrease in distribution rate but not elimination rate of gentamicin. For tylosin, there was a significant increase in elimination rate. These results indicate the kinetics of tylosin but not gentamicin are sufficiently altered as to support a need for increased frequency of administration with severe respiratory disease in calves.

Animals↗
PubMed1986

Intoxication of cattle by Perilla frutescens (purple mint).

Perilla frutescens or purple mint has been associated with atypical interstitial pneumonia (AIP) for a quarter of a century. The amount and the stage of the plant required to produce AIP have been much debated. A field case in which catastrophic loses occurred in cattle ingesting hay containing purple mint showed that more than the green plants have the capability of producing atypical interstitial pneumonia. In this study, Perilla frutescens produced atypical interstitial pneumonia in three of five calves to which it was given. The amount required to produce the syndrome ranged from 2.3 to 15.5 kg of green seed stage mint and 11.8 kg of mint hay. The toxic syndromes were similar in signs, but quite different in duration. Necropsy examinations showed varied amounts of pulmonary emphysema and edema. Two of the three affected animals' lungs histologically displayed a marked proliferation of Type II pneumocytes. The flowering or seed parts of perilla mint were found by high pressure liquid chromatographic analysis to contain the highest concentration of perilla ketone, considered the most toxic agent involved. This stage of plant growth was also shown to be the most toxic in our calf feeding trial. Calves fed the flowering plant developed the toxic syndrome while those fed earlier plants (collected before seed stage) and late plants (collected after frost) remained asymptomatic. The time of year when perilla reaches the seed stage often corresponds to periods when pasture grass is scarce forcing cattle to consume plants not normally eaten when ample desirable forage is available.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1985

Rifampin in the horse: comparison of intravenous, intramuscular, and oral administrations.

The plasma concentrations and pharmacokinetics of rifampin disposition were determined after a single IV, IM, or oral dose of 10 mg/kg of body weight and an oral dose of 25 mg/kg. The overall elimination rate constants per minute were similar for the 10 mg/kg dose (0.0021 +/- 0.0004, IV; 0.0017 +/- 0.0002, IM; and 0.0023 +/- 0.0006, orally). The apparent bioavailability was moderate to low for IM and oral administrations (59.8% +/- 3.2% and 39.5% +/- 5.0%, respectively). The rate of absorption was most rapid for oral administration with an absorption half-life of 249.7 +/- 71.6 minutes as compared with 403.5 +/- 89.7 minutes for IM administration. However, the IM route produced longer detectable plasma concentrations (50 hours in 2 of the 4 horses). Based on bacterial sensitivity information derived for human and canine isolates, the daily oral administration of 10 mg of rifampin/kg administered in the feed represents a reasonable dose for susceptible gram-positive bacterial pathogens. Higher doses (greater than or equal to 25 mg/kg) or IV administration would be required for most gram-negative bacteria. Adverse effects of sufficient severity to limit use of the drug, especially by the oral route of administration, were not encountered under the single-dose experimental conditions used.

Administration, Oral↗
PubMed1985

Effects of experimentally induced Pasteurella haemolytica pneumonia on the pharmacokinetics of erythromycin in the calf.

Pneumonic pasteurellosis was produced experimentally in 3- to 4-month-old Holstein bull calves by bilateral intrapulmonary administration of 5 X 10(7) to 10(9) colony-forming units of Pasteurella haemolytica. Of 8 calves, 4 developed minor pulmonary changes, 1 died of an apparent bacteremia within 24 hours, and 3 developed extensive pneumonic changes. At 1 week before (1 dose) and at 48, 60, and 72 hours (3 doses) after Pasteurella administration, the calves were given erythromycin at a dosage of 15 mg/kg, and the pharmacokinetic values were determined. There were statistically (P less than or equal to 0.05) significant increases in the distribution and elimination rates associated with pneumonia. The elimination half life decreased from 132.7 +/- 9.6 minutes in prepneumonic calves to 111.1 +/- 13.8 minutes and 99.7 +/- 2.6 minutes in calves with minor and with moderate pneumonic changes, respectively. There also was a decrease in apparent volume of distribution with pneumonia. Erythromycin tissue concentrations were determined 2 hours after the last dose was given to the calves with pneumonia. Tissue concentrations in the pneumonic lung areas were as high or higher than those in nonaffected lung tissues in the same animals. Because of the increased rate of elimination from serum in pneumonic calves, it may be advisable to use shorter dosage intervals in calves with severe respiratory tract disease.

Animals↗
PubMed1984

Recent perspectives on the toxicodynamic basis of cyanide antagonism.

The mechanism of action of nitrite-thiosulfate (Chen et al., 1933a ,b; Hug , 1933) in the antagonism of the lethal effects of cyanide is much more complex than proposed 50 years ago. Some of the recent findings concerning the mechanism of nitrite action have conceptual theoretical and practical significance, as the development of newer cyanide antagonists are dependent on the elucidation of the basic mechanism of antidotal action. There are preliminary evidence which suggest a vasogenic action rather than methemoglobin formation is the primary action of nitrite, as a cyanide antagonist. Various vasogenic compounds have been uncovered and they may play an important role in the future development of a new class of cyanide antagonists. Also recent development in thiol detoxication of cyanide suggest that rhodanese may play a more complex role. The detoxification of cyanide may be viewed from a considerably more complex perspective with the elucidation of recent mechanisms. It also may provide a newer conceptual basis for a more rational development of future compounds to antagonize the lethal effects of cyanide.

Animals↗
PubMed1984

Methylene blue: effects and disposition in sheep.

The disposition and urinary excretion pharmacokinetics of methylene blue were determined after its intravenous administration at 15 mg/kg to mature female sheep. Comparisons were made between methylene blue administered alone or subsequent to 50 mg/kg sodium nitrite. The overall elimination rate constant (beta) of methylene blue, 0.0076 +/- 0.0016 min-1, was not influenced by prior administration of sodium nitrite. However, the distribution rate was significantly altered by sodium nitrite. Very little of the methylene blue was eliminated in the urine either intact or as leucomethylene blue in spite of its relatively short half life. Toxicologic assessment was carried out using LD50 determination, methemoglobin production and hematologic effects as evaluation parameters. Methemoglobin production was minimal with doses as high as 50 mg/kg and no significant hematologic changes were seen up to 4 weeks after a total dose of 30 mg/kg methylene blue. The 24 h LD50 for intravenous methylene blue administered as a 3% solution was 42.3 mg/kg with 95% confidence interval limits of 37.3 to 47.9 mg/kg. From these data it appears that as conditions may warrant, the dosage of methylene blue may be safely increased up to at least 15 mg/kg in therapy of severe methemoglobinemias.

Animals↗
PubMed1984

Preliminary studies on the effect of yeast culture supplementation on nitrate/nitrite induced methemoglobinemia in lambs and steers.

Lambs and steers were fed low-nitrate hay and supplements which supplied 0.045 kg (lambs) or 0.114 kg (steers) of yeast culture/head/day for 14 and 12 days, respectively, prior to feeding high-nitrate sorghum-sudan hay. Nitrate consumption of lambs by 6 hours after feeding the high-nitrate (29,300 ppm NO3) hay was similar among treatments and ranged from 0.3 to 0.5 g/kg body weight/day over 3 challenge days. Similar rates of nitrate consumption occurred with steers. Blood methemoglobin concentrations, used as a measure of nitrate/nitrite exposure in lambs and steers fed yeast culture, were not lower than those of control animals. The results of the study indicate that yeast culture did not decrease the methemoglobinemia produced by consumption of high-nitrate forages by sheep or cattle.

Animal Feed↗
PubMed1984

Chloramphenicol and the neonatal calf.

Pharmacokinetic values and possible toxic effects of chloramphenicol on bone marrow and hematologic and serum chemical values were determined in newborn calves given the drug (IV) once a week or in repeated doses, 12 hours between doses. The rates of elimination for chloramphenicol and antipyrine also were compared. Chloramphenicol also was administered to older calves by IM and subcutaneous routes, with an apparent bioavailability of 50% to 60%. The elimination half-lives for both chloramphenicol and antipyrine were markedly increased in the newborn calf for at least the first 3 to 4 weeks of life. Despite the high and prolonged serum chloramphenicol concentrations in these calves, there was little or no indication of toxic effects. Bone marrow aspirates did not reveal any signs of intoxication such as cytoplasmic or nuclear vacuolation. Marrow cellularity was not recognizably different from the control group.

Age Factors↗
PubMed1983

Effect of oxytetracycline administration on antibody response to Brucella abortus vaccination in calves.

In 5- to 7-month-old dairy calves, concurrent oxytetracycline administration and subcutaneous vaccination with 10(9) Brucella abortus strain 19 organisms reduced the percentage of animals with detectable humoral antibodies to Brucella abortus, when compared with untreated vaccinated calves of the same age range. The reduction of antibody reaction in the card test was less than that associated with the injection of 10(9) heat-killed Brucella abortus strain 19 organisms.

Animals↗
PubMed1983

Allergy to laboratory animals: a retrospective and a prospective study.

Twenty four volunteers who had been allergic to laboratory animals for some years were examined by means of a questionnaire paying particular attention to symptoms associated with rats and by serological and skin tests with extracts of rat urine (retrospective study). Nasal and eye symptoms were reported by 21 and 16 individuals respectively: 13 had asthma. Positive skin tests and high levels of specific IgE antibody to rat urine extract were found in 17 of the more severely affected individuals and this group included 12 of those with asthma. Latent periods of work with animals before symptoms appeared varied from 0.5 to 12 years. Also 148 individuals were studied during their first year of work with animals (prospective study). Symptoms developing during the year were reported by 15%, asthma by 2%. IgE antibody levels to rat urine were raised in 40% of affected and 6% of the unaffected individuals but there was no significant correlation between symptoms and either antibody levels or positive skin tests. Allergic symptoms developing during the first year of postemployment were, on the whole, much milder than those seen in the retrospective study. A tentative conclusion is that most individuals who become allergic to laboratory animals develop the condition in a mild form during their first year of employment but it appears probable that atopic individuals, although having an equal chance of developing allergy as compared with non-atopic individuals, may eventually progress to a more severe form of the disease.

Allergens↗
PubMed1983

Comparative pharmacokinetics of antibiotics in newborn calves: chloramphenicol, lincomycin, and tylosin.

The pharmacokinetics of 3 antibiotics--chloramphenicol, lincomycin, and tylosin--were determined in newborn calves. The kinetic determinations, using 2-compartment open models, were made at increasing ages from 1 day to 42 days and compared with those made from 9-month-old calves. Although all 3 antibiotics require a degree of hepatic metabolism, there were marked differences in the development of elimination processes for the individual drugs. Elimination of tylosin, which was slow in the calves at birth, increased rapidly and was equal to that in older calves by the end of 1 week. Lincomycin elimination was not markedly reduced in calves at birth. Chloramphenicol elimination was slow in calves at birth and only by 4 to 6 weeks attained the rate found in older calves. Dosage adjustments would not be required for the antibiotics tylosin or lincomycin when given to newborn calves, but may be necessary for chloramphenicol given to calves before they are 4 to 6 weeks old.

Age Factors↗