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Pharmacokinetics of gentamicin in mares in late pregnancy and early lactation.
Abstract: The disposition of drugs may differ between pregnant and nonpregnant animals, necessitating a change in dosage. We hypothesized that volume of distribution or clearance may be different for aminoglycoside antibiotics in pregnant mares vs. nonpregnant lactating mares. To examine this hypothesis, we administered gentamicin sulfate to seven Thoroughbred and Quarterhorse mares on two occasions, followed by plasma drug gentamicin assay and pharmacokinetic analysis. The first dose was administered 1-4 weeks before parturition (mean weight 578 kg) and the second dose was administered in the period 1-4 weeks after parturition (mean weight 518 kg). The dose administered at each time was approximately 6.6 mg/kg, intravenously (i.v.). Plasma gentamicin concentrations were determined using fluorescence polarization immunoassay and pharmacokinetic analysis was performed using a two-compartment open model. The plasma concentration vs. time profiles and total area-under-the-curve were almost identical for mares at late gestation vs. early lactation. Mean volume of distribution at steady-state was 0.15 (+/-0.02) and 0.16 (+/-0.03) L/kg, systemic clearance was 1.06 (+/-0.17) and 1.11 (+/-0.17) mL/kg/min, and mean (harmonic) elimination half-life was 2.2 and 2.1 h, for pregnant and nonpregnant mares, respectively. We concluded that there were no differences in drug distribution and clearance between pregnant and nonpregnant lactating mares. Gentamicin was also assayed in plasma of newborn foals after an injection of 6.6 mg/kg to three of the mares within 60 min of parturition. Gentamicin was undetectable in plasma samples from these foals and, therefore, apparently does not cross the placenta of mares at term.
Publication Date: 2001-02-13 PubMed ID: 11168913DOI: 10.1046/j.1365-2885.2000.00298.xGoogle Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
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This study explores the changes in drug behavior between pregnant and lactating horses, focusing on the aminoglycoside antibiotic, gentamicin. The research concluded that there was no significant difference in drug distribution and clearance between pregnant and lactating horses, also finding that the antibiotic does not cross the placenta.
Experimental Process
- The researchers conducted their study on seven mares of the Thoroughbred and Quarterhorse breeds. These subjects were tested twice — once late in pregnancy and then again early in lactation.
- The antibiotic gentamicin sulfate was administered at approximately 6.6 mg/kg through intravenous injection each time.
- The time frames for the doses were: first injection 1-4 weeks before birth and second injection 1-4 weeks after birth. It’s important to note that the average weight of mares differs between these two time frames, with mean weight being 578 kg before parturition and 518 kg after.
- The researchers used a fluorescence polarization immunoassay for determining gentamicin levels in the plasma and a two-compartment open model for the pharmacokinetic analysis.
Research Findings
- Comparing plasma concentration against time and total area-under-the-curve, researchers found near identical results for late pregnancy and early lactation horses. This indicates that there is no significant difference in gentamicin behavior between these two states.
- The mean volume distribution was 0.15 L/kg and 0.16 L/kg, systemic clearance was 1.06 mL/kg/min and 1.11 mL/kg/min, and mean elimination half-life was 2.2 and 2.1 hours, for pregnant and nonpregnant horses, respectively. These substantially consistent values reinforced the conclusion of no significant difference in drug behavior between pregnant and lactating horses.
Implication for Foals
- Gentamicin was also tested on newborn foals. The mares were injected with a dosage of 6.6 mg/kg within 60 minutes after birth and the plasma samples from the foals were analyzed.
- Researchers found no evidence of gentamicin in the foals’ plasma, which suggests that the antibiotic does not cross the placenta of mares at term.
Cite This Article
APA
Santschi EM, Papich MG.
(2001).
Pharmacokinetics of gentamicin in mares in late pregnancy and early lactation.
J Vet Pharmacol Ther, 23(6), 359-363.
https://doi.org/10.1046/j.1365-2885.2000.00298.x Publication
Researcher Affiliations
- School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin, USA.
MeSH Terms
- Animals
- Anti-Bacterial Agents / blood
- Anti-Bacterial Agents / pharmacokinetics
- Area Under Curve
- Female
- Fluorescence Polarization Immunoassay
- Gentamicins / blood
- Gentamicins / pharmacokinetics
- Half-Life
- Horses
- Injections, Intravenous
- Lactation
- Metabolic Clearance Rate
- Pregnancy
Citations
This article has been cited 4 times.- Rosa B. Equine Drug Transporters: A Mini-Review and Veterinary Perspective. Pharmaceutics 2020 Nov 8;12(11).
- Cummins C, Carrington S, Fitzpatrick E, Duggan V. Ascending placentitis in the mare: A review. Ir Vet J 2008 May 1;61(5):307-13.
- Rebuelto M, Loza ME. Antibiotic Treatment of Dogs and Cats during Pregnancy. Vet Med Int 2010 Dec 14;2010:385640.
- Bailey CS, Beachler TM, Mochel JP, Wulf LW, Yaeger M, Kundu D, Withowski K, Papich MG. Penicillin and Gentamicin Concentrations in the Uterine Fluid of Non-Pregnant Mares Following a Single Intrauterine Infusion. J Vet Pharmacol Ther 2025 Sep;48(5):389-396.
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