What Is Buserelin?

Buserelin is a synthetic luteinizing hormone–releasing hormone (LHRH) analog. Like naturally occurring LHRH that is produced by the hypothalamus, initial or intermittent administration of buserelin stimulates release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary.¹ In humans, branded forms of buserelin are used primarily in the treatment of prostate cancer and endometriosis.

Clinical trials conducted several years ago demonstrated that treating mares with buserelin 9 or 10 days after ovulation increases pregnancy rates. "Early embryonic loss is a major cause of sub-fertility in mares. Progesterone produced in the ovary by the corpus luteum maintains the early pregnancy. The embryo must signal its presence and ensure the corpus luteum is maintained in order to survive the first few weeks of pregnancy. In other species, luteal function in pregnant animals starts to diverge from that of non-pregnant animals between 11 and 14 days after ovulation. It is therefore, considered to be a critical time for the maintenance of the pregnancy."² Since then, buserelin has been offered under several trademarks and has become a popular medication for the prevention of embryonic loss in mares.

"We observed structural changes in the follicles and uterus of heavy draft mares during estrus and examined the effect of a single injection of the gonadotropin-releasing hormone analog buserelin on ovulation and endocrine profiles. Twenty-two heavy draft mares were divided into a buserelin-treated group (n=8) and a control group (n=14). Mares were given an intramuscular injection of 40 µg buserelin when they presented signs of estrus to a teaser stallion, had ≥45 mm diameter follicles, and presented decreased uterine edema compared with the previous examination. The follicles and uterus were monitored using transrectal ultrasound imaging and measurement of blood levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone, and estradiol-17β.

[R]esults indicate that a single injection of 40 µg buserelin when follicles are at least 45 mm in diameter and uterine edema is decreased is effective for inducing ovulation."³

Buserelin is also employed in order to induce ovulation in cyclic mares. For this purpose, hCG has frequently been used, but efficacy often diminishes after successive administrations. Buserelin with hCG is as effective as hCG by itself in inducing ovulation between 24 and 48 hours after initiation of treatment without the diminishing effectiveness of hCG over time.

"Buserelin treatment induced a rise in LH concentration during the 48 h period of the experiment, and LH concentrations before ovulation were significantly higher in buserelin treated cycles than in placebo cycles. These experiments demonstrated the usefulness of two new protocols of administration of buserelin, as an alternative to hCG for induction of ovulation. One hypothesis explaining the mechanism of action is that the persistant rise in LH concentration could modify the ratio of biological/immunological LH, as it occurs physiologically, thereby hastening ovulation."⁴

According to the available research, side effects in equines where buserelin is used are reported as minimal.

¹Huben RP, Murphy GP, et. al. A comparison of diethylstilbestrol or orchiectomy with buserelin and with methotrexate plus diethylstilbestrol or orchiectomy in newly diagnosed patients with clinical stage D2 cancer of the prostate. Cancer 1988 Nov 1; 62: 1881-7.

²Newcombe, J.R., Martinez, T.A., et. al. The effect of the gonadotropin-releasing hormone analog, buserelin, on pregnancy rates in horse and pony mares. Theriogenology, (2001) 55, 1619-1631.

³Miki W, Oniyama H, Takeda N, et al. Effects of a single use of the GnRH analog buserelin on the induction of ovulation and endocrine profiles in heavy draft mares. J Equine Sci. 2016;27(4):149–156. doi:10.1294/jes.27.149

⁴Barrier-Battut, I., Poutre, N., et. al. (2001). Use of buserelin to induce ovulation in cyclic mares. Theriogenology. 55. 1679-95. 10.1016/S0093-691X(01)00512-X.

About NexGen Pharmaceuticals

NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services Nationwide. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.

Our pharmacists are also encouraged to develop strong working relationships with our veterinarians in order to better care for veterinary patients. Such relationships foster an ever-increasing knowledge base upon which pharmacists and veterinarians can draw, making both significantly more effective in their professional roles.