Buserelin

Overview

Buserelin is a synthetic nonapeptide GnRH agonist developed by Hoechst (now Sanofi) in the 1970s and approved in many countries under brand names including Suprefact and Suprecur. It is used for the palliative treatment of advanced hormone-dependent prostate cancer, endometriosis, uterine fibroids, and controlled ovarian stimulation in assisted reproductive technology (ART). Buserelin was one of the earliest GnRH analogs in widespread clinical use and helped establish the paradigm of reversible medical castration for prostate malignancy.

Buserelin belongs to the same therapeutic class as leuprolide, goserelin, triptorelin, nafarelin, and histrelin. Unlike degarelix, a GnRH antagonist, buserelin produces an initial testosterone flare before achieving chemical castration.

Structure / Sequence

The sequence of buserelin is pGlu-His-Trp-Ser-Tyr-D-Ser(tBu)-Leu-Arg-Pro-NHEt. The two principal modifications are D-serine(tert-butyl) at position 6 and replacement of the C-terminal glycinamide with an N-ethyl proline amide. These changes resist enzymatic cleavage by pyroglutamyl peptidase and endopeptidases, extending half-life and multiplying receptor potency relative to native GnRH by roughly 20 to 50 times.

Mechanism of Action

Buserelin is a potent, long-acting agonist at the pituitary GnRH receptor. Acute administration causes release of LH and FSH with a resulting surge in testosterone or estradiol, the "flare" phase. Continuous, non-pulsatile receptor activation over 10 to 14 days induces receptor downregulation and uncoupling from downstream Gq signaling, suppressing LH, FSH, testosterone, and estradiol to castrate levels. The duration and depth of suppression underlie its efficacy in hormone-dependent cancers and estrogen-sensitive gynecologic conditions.

Research Summary

Pharmacokinetics

Subcutaneous buserelin reaches peak plasma concentration within 60 minutes with a plasma half-life near 80 minutes. Intranasal bioavailability is 2 to 3 percent, requiring higher dosing frequency. Depot formulations (6.3 mg and 9.45 mg implants) maintain therapeutic concentrations for 2 or 3 months. Elimination is primarily through peptidase hydrolysis with renal excretion of metabolites. Dose adjustments are generally not required in mild to moderate renal impairment.

Dosing Protocols

• Prostate cancer: 500 mcg subcutaneously every 8 hours for 7 days, then 200 mcg intranasally three times daily, or 6.3 mg depot implant every 2 months
• Endometriosis: 900 mcg intranasally daily in three divided doses, up to 6 months
• IVF protocols: 200 to 500 mcg subcutaneously daily for pituitary downregulation
• Uterine fibroids: Depot or intranasal regimens for 3 to 6 months pre-surgery

An antiandrogen such as bicalutamide is typically co-administered for 2 to 4 weeks around initiation to blunt flare in prostate cancer.

Common Discussion Topics

• Flare prevention strategies at prostate cancer initiation
• Bone mineral density loss with chronic GnRH agonist therapy
• Buserelin versus leuprolide depot pharmacokinetics
• Use in IVF downregulation protocols alongside gonadorelin antagonists
• Add-back therapy (low-dose estrogen/progestin) during endometriosis treatment

Related Compounds

• Leuprolide — depot GnRH agonist
• Triptorelin — long-acting GnRH agonist
• Nafarelin — intranasal GnRH agonist
• Histrelin — 12-month GnRH agonist implant
• Degarelix — GnRH antagonist
• Gonadorelin — native GnRH
• Alarelin — veterinary GnRH agonist