Disposition of gentamicin in the genital tract of cows

Use of tissue-fluid correlations to estimate gentamicin residues in kidney tissue of Holstein steers

Gentamicin continues to be one of the most effective antibiotics for the treatment of gram-negative infections. Greater than 90% of the drug is rapidly eliminated from the body in <2 days, however, a small residue remains bound to the kidney cortex tissue for many months. In beef steers, the gentamicin residue is unacceptable and its presence is monitored by the FAST (Fast Antimicrobial Screen Test) applied to the kidney at the time of slaughter. The sensitivity of the FAST to gentamicin in the kidney cortex is reported to be 100 ng/g, therefore, this level of gentamicin defines the acceptable limit of gentamicin drug residue in the bovine kidney. In the present study, three doses of 4 mg/kg gentamicin was administered intramuscularly to eight steers. Gentamicin was allowed to deplete from the kidneys for a range of times from 7 to 10 months. At slaughter the level of gentamicin in the kidney cortex varied from 91 to 193 ng/g, but a total of 160 FAST tests performed on the kidneys were negative. Blood and urine samples were collected at varying times following the last dose of gentamicin. Kidney tissue samples were collected by laparoscopic surgery in the live steers as well as the final sample obtained at slaughter. Plasma levels of gentamicin declined rapidly to nondetectable within 3 days, while measurable urine persisted for 75 days before the concentration of gentamicin declined to levels too low to quantitate by the available liquid chromatography tandem mass spectrometry (LC/MS/MS) technique. An estimated correlation between an extrapolation of urine gentamicin concentration to the corresponding kidney tissue sample suggests a urine to kidney tissue relationship of 1:100. A test system sufficiently sensitive to a urine gentamicin concentration of 1 ng/mL will correlate with the estimated 100 ng/g gentamicin limit of the FAST applied to the fresh kidney of the recently slaughtered bovine.

Effect of sexual steroid hormones on spiramycin disposition in genital tract secretions of the ewe

The present work investigated the influence of sexual steroid compounds (estradiol 17 beta and fluorogestone) on antibiotic passage across the uterine barrier. Five healthy and mature ewes, with controlled hormonal impregnation, were given a single iv injection of spiramycin, a macrolide antibiotic, at a dose of 64,000 IU/kg. Plasma and uterine secretions were regularly sampled before the injection and for 30 h post-injection. Blood was collected from the jugular vein and uterine secretions were obtained by uterine flushing with a sterile saline solution containing 0.2% inulin. Spiramycin was concentrated in the uterine secretions, whatever the hormonal status; the secretions-to-plasma ratio was 4.68 +/- 1.88 under estrogen priming and 2.68 +/- 0.91 under progestagen priming. The area under the concentration-time curve (AUC) and the mean residence time (MRT) were significantly higher (p less than 0.001) in uterine secretions than in plasma. The AUC in uterine secretions was significantly higher (p less than 0.05) under estrogen priming (439.07 +/- 241.25 IU.h/mL) than under progestagen priming (141.41 +/- 89.37 IU.h/mL). The spiramycin MRTs in uterine secretions were 11.92 +/- 4.08 and 12.06 +/- 3.35 h for both estrogens and progestagen treatment, respectively. These experiments demonstrate that estrogens increase uterine bioavailability, but not the residence time, of spiramycin when administered by a systemic route.

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.

Pharmacokinetic aspects of penicillins, aminoglycosides and chloramphenicol in birds compared to mammals. A review

Based on a review of the literature, a comparison is made of the pharmacokinetics of penicillins, aminoglycosides, and chloramphenicol in birds and mammals. Penicillins in birds are likely to be more dependent for their elimination on biotransformation than in mammals. Amoxycillin had a relatively low availability (0.34) after p.o. administration. Higher doses (2 to 8 times) were needed to achieve the same peak levels in birds and mammals. Aminoglycosides, which for their elimination largely depend on renal excretion by glomerular filtration, show only minor differences in pharmacokinetics between birds and mammals. Chloramphenicol is mainly excreted after biotransformation and large differences in pharmacokinetic parameters are to be found, not only between birds and mammals, but also between avian species.