Pharmacokinetics of Intrauterine Ciprofloxacin in the Mare and Establishment of Minimum Inhibitory Concentrations for Equine Uterine Bacterial Isolates

Clinical Aspects of Bacterial Distribution and Antibiotic Resistance in the Reproductive System of Equids

Antibiotic administration is a standard therapeutic practice for the treatment of reproductive disorders of equids. This might lead to undesirable microbial imbalance and could favour the acquisition of antibiotic resistance. Therefore, it is imperative for clinicians to understand patterns of antibiotic resistance when considering and developing treatment regimes. Continued engagement of clinicians with novel alternative approaches to treat reproductive infections would be essential in order to address this rising threat within the One Health perspective. The objectives of the present review were to present the bacterial infections in the reproductive system of equids (horses, donkeys), to upraise the literature related to the issue of antibiotic resistance of bacteria causing these infections and to discuss the topic from a clinical perspective. Initially, the review summarised the various infections of the reproductive system of equids (genital system of females, genital system of males, mammary glands) and the causal bacteria, providing relevant information about horses and donkeys. Subsequently, the clinical therapeutics of these infections were presented, taking into account the significance of antibiotic resistance of bacteria as a limiting factor in treating the infections. Finally, approaches to circumvent antibiotic resistance in clinical settings were summarized. It was concluded that awareness regarding antibiotic resistance in equine reproductive medicine would increase, as we would recognise the multifaceted problem of resistance. Actions and initiatives within the One Health approach, minimizing the potential dissemination of resistant strains to humans and to the environment, with specific applications in medicine of equids should be appropriately instituted internationally.

Antimicrobial Resistance in Equine Reproduction

Bacteria develop resistance to antibiotics following low-level "background" exposure to antimicrobial agents as well as from exposure at therapeutic levels during treatment for bacterial infections. In this review, we look specifically at antimicrobial resistance (AMR) in the equine reproductive tract and its possible origin, focusing particularly on antibiotics in semen extenders used in preparing semen doses for artificial insemination. Our review of the literature indicated that AMR in the equine uterus and vagina were reported worldwide in the last 20 years, in locations as diverse as Europe, India, and the United States. Bacteria colonizing the mucosa of the reproductive tract are transferred to semen during collection; further contamination of the semen may occur during processing, despite strict attention to hygiene at critical control points. These bacteria compete with spermatozoa for nutrients in the semen extender, producing metabolic byproducts and toxins that have a detrimental effect on sperm quality. Potential pathogens such as Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa may occasionally cause fertility issues in inseminated mares. Antibiotics are added during semen processing, according to legislation, to impede the growth of these microorganisms but may have a detrimental effect on sperm quality, depending on the antimicrobial agent and concentration used. However, this addition of antibiotics is counter to current recommendations on the prudent use of antibiotics, which recommend that antibiotics should be used only for therapeutic purposes and after establishing bacterial sensitivity. There is some evidence of resistance among bacteria found in semen samples. Potential alternatives to the addition of antibiotics are considered, especially physical removal separation of spermatozoa from bacteria. Suggestions for further research with colloid centrifugation are provided.

Pharmacokinetics of intravenous and oral administration of enrofloxacin to the late-term pregnant and non-pregnant mares

BACKGROUND

Enrofloxacin may be an alternative antimicrobial for unresponsive cases of severe bacterial infections in pregnant mares. As pregnancy may affect drug bioavailability, distribution, metabolism and excretion, dose adjustment might be necessary.

OBJECTIVES

To determine the disposition of orally and intravenously administered enrofloxacin in pregnant and non-pregnant mares.

STUDY DESIGN

Randomised cross-over experiment.

METHODS

Six light-breed, healthy pregnant mares (260 days gestation) were given a single dose of either intravenous (5 mg/kg bwt) or oral compounded (7.5 mg/kg bwt) enrofloxacin, with the opposite dose administered after a 7-day washout. The protocol was repeated 45-60 days post-partum, 15-30 days after foals were weaned. Plasma samples were obtained via venepuncture at 0, 5, 10, 20, 30, 45, 60, 90 min, and 2, 3, 4, 6, 8, 12, 24, 36, 48 and 72 h after enrofloxacin administration. Enrofloxacin and ciprofloxacin concentrations were measured by LC-MS/MS. Concentration versus time data were analysed based on non-compartmental pharmacokinetics.

RESULTS

Enrofloxacin AUC_0-∞ was significantly higher in pregnant mares than non-pregnant mares after PO administration and tended to be higher after i.v. administration. Ciprofloxacin maximum plasma concentration (C_max ) and concentration at 24 h (C_24h ) were higher, and half-life of the terminal phase (t_½λz ) was longer in pregnant mares than non-pregnant mares after oral administration. Similarly, ciprofloxacin C_24h was higher in pregnant mares with intravenous administration. Oral bioavailability did not differ based on pregnancy status.

MAIN LIMITATIONS

Only six healthy light breed mares were assessed. Disease or horse breed may affect the endpoints evaluated. A lack of established enrofloxacin AUC/MIC targets for equine pathogens limits pharmacokinetic-pharmacodynamic conclusions.

CONCLUSIONS

The oral form of enrofloxacin was well absorbed, and oral bioavailability was comparable to previous studies. While differences in enrofloxacin and ciprofloxacin pharmacokinetics were seen between pregnant and non-pregnant mares, the recommended drug dose and dose intervals are appropriate for MIC <0.25 µg/mL. Dosages may need to be adjusted for bacteria with a MIC >0.25 µg/mL.

Diffusion of enrofloxacin to pregnancy fluids and effects on fetal cartilage after intravenous administration to late pregnant mares

BACKGROUND

In selective cases, enrofloxacin may be an alternative antibacterial agent to treat unresponsive infections in pregnant mares. Supratherapeutic doses of enrofloxacin are toxic to adult horses and also to newborn foals, however, it is unknown if enrofloxacin crosses the equine placenta or if it is toxic to the fetus.

OBJECTIVES

To assess the diffusion of enrofloxacin and its metabolite to fetal fluids and its effects on fetal cartilage when administered to pregnant mares.

STUDY DESIGN

In vivo and terminal controlled experiment.

METHODS

Healthy mares at 260 days of gestation were allocated into three groups: untreated (n = 3), therapeutic treatment (5 mg/kg enrofloxacin, i.v., n = 7) or supratherapeutic treatment (10 mg/kg, i.v., n = 6) for 11 days. Fetal fluids were collected on days 1, 5 and 11 of treatment. Premature delivery was induced on day 11 with oxytocin and fetal fluids and plasma were collected during delivery. Plasma and fetal fluid enrofloxacin and ciprofloxacin concentrations were measured by liquid chromatography-mass spectrometry. Fetal articular cartilage was examined macroscopically and histologically for lesions.

RESULTS

Enrofloxacin and ciprofloxacin reached the minimum inhibitory concentrations for common pathogens in all fluids. Ciprofloxacin did not increase with the double enrofloxacin dose in maternal plasma, but allantoic fluid showed a 10-fold increase relative to fetal trough plasma concentrations. Administration of enrofloxacin at recommended doses did not result in cartilaginous lesions in fetuses.

MAIN LIMITATIONS

Only one time point in gestation was evaluated and mares treated in the study were healthy at the time of treatment. It remains to be determined if enrofloxacin shows toxicity at other stages of pregnancy, after a longer duration of treatment, or once the foals are delivered and articular surfaces are weightbearing.

CONCLUSIONS

Short-term administration of enrofloxacin to late gestation mares resulted in detectable enrofloxacin and ciprofloxacin concentrations in fetal fluids and did not result in macroscopic or microscopic lesions in the fetus. While further research is needed to address long-term foal outcomes, enrofloxacin may be useful for select bacterial infections in pregnant mares.