Intravenous clomiphene citrate pharmacokinetics in healthy mares as a first step toward use in reproduction.

Overview

• This study examined how clomiphene citrate (CC), a drug that interacts with estrogen receptors, behaves in the bloodstream of healthy mares when given intravenously.
• The goal was to determine suitable dosing and understand its pharmacokinetics before considering its use to enhance reproductive outcomes in horses.

Background and Purpose

• Clomiphene citrate (CC) is a selective estrogen receptor modulator commonly used in human medicine to influence reproductive hormones.
• Its effects on horse reproduction remain poorly understood, necessitating pharmacokinetic studies to explore safe and effective use.
• The study aimed to analyze the pharmacokinetic parameters of intravenous (IV) CC administration in healthy mares as a foundation for potential reproductive applications.

Methodology

• Experimental design involved two phases:
• Single-Dose Phase: Eight healthy mares received one IV dose of 2,000 mg CC. Plasma samples were collected over 336 hours (14 days) to measure drug concentration over time.
• Multidose Phase: Six mares received 2,000 mg of IV CC every 24 hours for 5 days to assess trough (lowest) plasma drug concentrations daily.
• Drug tolerance and potential side effects were monitored throughout the study.

Key Findings

• Tolerability: Clomiphene citrate was well tolerated by all mares, with no significant adverse effects noted.
• Pharmacokinetics:
  • Elimination half-life was approximately 4.95 hours (±1.10), indicating CC is cleared relatively quickly from the mare’s system.
  • Mean residence time—the average time the drug stays in the body—was about 7.14 hours (±1.59).
  • Peak plasma concentrations reached levels comparable to those considered therapeutic in human females.
  • Trough concentration data from the multidose regimen suggested drug accumulation patterns and helped gauge appropriate dosing intervals.
• Dosing Implications: The study indicates that a 2,000 mg IV dose of CC achieves plasma levels presumed to be therapeutic in mares.
• Administration Frequency: Based on the multidose data, dosing intervals of every 12 to 24 hours may be needed to maintain effective plasma drug levels.

Conclusions and Future Directions

• Intravenous administration of clomiphene citrate is safe and achieves potentially effective drug concentrations in mares.
• These pharmacokinetic data provide a foundation for future research into CC’s role in enhancing equine reproductive technologies, such as in vitro embryo production.
• Further fertility trials are necessary to determine whether CC can increase the efficiency and success rates of such reproductive interventions in horses.