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

Objective: To investigate the IV pharmacokinetic parameters of clomiphene citrate (CC), a selective estrogen receptor modulator, in mares.

Methods: This was an experimental study to assess the pharmacokinetic parameters of CC in the mare. Eight mares received a single 2,000-mg dose of IV CC to identify plasma concentrations over 336 hours. Following this, 6 mares received a multidose regimen of IV CC (2,000 mg, q 24 h) for 5 days to identify trough plasma concentration each day.

Results: CC was well tolerated, demonstrated a short elimination half-life of 4.95 ± 1.10 hours and a mean residence time of 7.14 ± 1.59 hours, and reached plasma drug concentrations considered to be therapeutic in women. Peak and trough plasma concentrations were determined.

Conclusions: IV CC at 2,000 mg reaches presumed therapeutic concentrations in the mare. Based on the multidose trial, 2,000 mg of IV CC may require administration every 12 to 24 hours.

Clinical relevance: IV CC appears to be well tolerated in the mare. Future fertility trials are warranted to assess the potential that CC may have in increasing the efficiency of equine in vitro embryo production.