Buserelin is a synthetic nonapeptide analogue of naturally occurring gonadotropin-releasing hormone (GnRH or LHRH). It acts as a potent GnRH agonist. Initially, it stimulates the pituitary gland to release luteinizing hormone (LH) and follicle-stimulating hormone (FSH), leading to a transient surge in sex hormone production (flare-up). With continuous administration, it causes a profound down-regulation and desensitization of pituitary GnRH receptors, leading to a sustained suppression of gonadotropin secretion and, consequently, a medical castration or suppression of ovarian/testicular steroidogenesis. The 5mg strength is typically formulated as a long-acting depot injection for subcutaneous or intramuscular administration, used primarily in advanced hormone-dependent cancers and central precocious puberty.
Adult: Prostate/Breast Cancer: 5mg administered as a subcutaneous or intramuscular depot injection once every 28 days (monthly). Endometriosis/Fibroids: 5mg SC/IM depot once every 28 days for a maximum of 6 months.
Note: For subcutaneous use: Inject into the anterior abdominal wall, thigh, or upper arm, rotating sites. For intramuscular use: Inject deep into a large muscle (gluteus). The depot suspension must be reconstituted strictly as per the manufacturer's instructions provided with the specific brand. Administer immediately after reconstitution. Ensure patient is monitored for initial tumor flare reaction.
Buserelin is a superagonist of the hypothalamic GnRH receptor. Its higher potency and longer receptor occupancy compared to native GnRH lead to an initial, exaggerated release of LH and FSH from the anterior pituitary. With continuous administration, the sustained receptor occupancy causes internalization and down-regulation of GnRH receptors on pituitary gonadotrophs. This leads to desensitization and a profound suppression of the synthesis and release of LH and FSH. The resultant hypogonadotropic state inhibits gonadal production of sex steroids (testosterone and dihydrotestosterone in males, estrogen in females).
Pregnancy: CONTRANDICATED - Category X. Can cause fetal harm, including loss of pregnancy and potential teratogenic effects. Exclude pregnancy before starting therapy. Advise use of non-hormonal contraception during and for some time after treatment.
Driving: May cause fatigue, dizziness, or visual disturbances. Patients should be cautioned about operating machinery or driving until they know how the drug affects them.
| Androgen Receptor Antagonists (e.g., Bicalutamide, Flutamide) | Used concomitantly to block the initial testosterone flare in prostate cancer. Synergistic therapeutic effect. | Major (Therapeutic) |
| Drugs that Prolong QT Interval (e.g., Class IA/III antiarrhythmics, certain antipsychotics, antibiotics) | Additive risk of QT prolongation and cardiac arrhythmias. Buserelin may lower testosterone/estrogen, which can affect cardiac repolarization. | Major |
| Corticosteroids (e.g., Dexamethasone) | May diminish the therapeutic effect of Buserelin by suppressing pituitary response. | Moderate |
| Sex Hormones (e.g., Testosterone, Estrogen therapy) | Counteracts the therapeutic hypogonadal effect of Buserelin. | Major |
Same composition (Buserelin (5mg)), different brands: