Buserelin

Mechanism

Buserelin is a synthetic nonapeptide analogue of endogenous GnRH (decapeptide). Key structural modifications include: (1) substitution of glycine at position 6 with D-serine (D-Ser(tBu)⁶), enhancing resistance to enzymatic degradation and increasing receptor binding affinity; and (2) replacement of the C-terminal glycinamide with ethylamide (ProNHEt⁹), further improving metabolic stability. These modifications extend the half-life from GnRH's 2-4 minutes to approximately 80 minutes. Buserelin binds to GnRH receptors on anterior pituitary gonadotrophs with high affinity. The initial agonist binding stimulates a burst of FSH and LH release (the 'flare' effect, lasting 5-12 days). However, continuous receptor occupation causes desensitisation and downregulation of GnRH receptors, post-receptor signalling uncoupling, and depletion of releasable gonadotropin stores. The net result after 1-3 weeks of continuous therapy is profound suppression of FSH and LH, leading to suppressed gonadal steroidogenesis: testosterone falls to castrate levels in men; oestradiol falls to postmenopausal levels in women. This suppression is reversible upon discontinuation.

Evidence base

Key Evidence

1. Prostate cancer meta-analysis: Schmitt B, et al. Cochrane Database of Systematic Reviews. Multiple GnRH agonist trials confirm equivalent efficacy across the class for advanced prostate cancer.

2. Endometriosis: Brown J, et al. Cochrane Database of Systematic Reviews. 2009. GnRH agonists effective for endometriosis-associated pain; equivalent efficacy within the class.

3. IVF protocols: The Cochrane review of GnRH agonist protocols for IVF (Al-Inany HG, et al.) confirmed that long-protocol GnRH agonist downregulation remains a standard approach with good outcomes.

4. Comparative GnRH agonist studies: Buserelin has been shown to achieve equivalent testosterone suppression to goserelin and leuprorelin in multiple head-to-head and observational studies.

Regulatory Status

• FDA approval: Buserelin is available in some markets; not as widely used in the US as leuprorelin/goserelin
• EMA/MHRA: Licensed for prostate cancer, endometriosis, uterine fibroids, precocious puberty, and IVF
• NICE guidance: Referenced in prostate cancer (NG131) and endometriosis management guidelines

Protocols

Buserelin is available as:

• Nasal spray (Suprefact): 150 µg per spray per nostril. Typical dosing: 300 µg (one spray per nostril) three times daily = 900 µg/day total. Varies by indication.
• Subcutaneous depot (Suprefact Depot): 3.3 mg or 6.6 mg every 4-8 weeks for long-term suppression.
• IVF downregulation: Nasal spray or subcutaneous, started mid-luteal phase, continued until downregulation confirmed (oestradiol <200 pmol/L, endometrium <5mm).

These details are for research documentation. Buserelin is a prescription-only medicine and is not available for self-directed research use. No research peptide vendor sells buserelin.

UK legal status

Buserelin is a prescription-only medicine (POM) in the UK under the Human Medicines Regulations 2012. It is not a controlled substance under the Misuse of Drugs Act. It is not legally available as a research chemical.

Key points:

• MHRA status: Licensed medicinal product (Suprefact, Sanofi)
• Prescription requirement: Requires a valid prescription from a registered medical practitioner in urology, gynaecology, or reproductive medicine
• NHS availability: Widely available through the NHS for licensed indications
• Importation: Personal importation without a prescription is not legal

This compound is included in the Peptide Data knowledge base for educational completeness, given its significance as a GnRH-pathway peptide. It is not available through any UK research peptide vendor.

Vendor notes

Buserelin is not available through any UK research peptide vendor. It is a licensed prescription medicine dispensed exclusively through pharmacies with a valid prescription. No vendor profile on Peptide Data lists buserelin, and none should.