Histrelin

Overview

Histrelin is a synthetic GnRH agonist nonapeptide formulated as a once-yearly subcutaneous implant, marketed as Vantas for advanced prostate cancer and Supprelin LA for central precocious puberty (CPP) in children. Developed by Endo Pharmaceuticals and approved by the FDA in 2004 (Vantas) and 2007 (Supprelin LA), histrelin delivers continuous low-dose peptide release over 12 months via a flexible hydrogel reservoir implant placed in the inner upper arm. The implant model reduces adherence burden compared with monthly depots such as leuprolide.

Histrelin is chemically and pharmacologically similar to buserelin, triptorelin, and nafarelin, and is used for the same indications of hormone-dependent prostate cancer and estrogen- or testosterone-driven disorders.

Structure / Sequence

The sequence of histrelin is pGlu-His-Trp-Ser-Tyr-D-His(N-benzyl)-Leu-Arg-Pro-NHEt. The distinctive modification is D-histidine benzylated at the imidazole nitrogen at position 6, plus replacement of C-terminal Gly-NH2 with N-ethyl prolinamide. These changes confer resistance to peptidase cleavage and yield receptor potency approximately 100-fold greater than native GnRH.

Mechanism of Action

Histrelin binds the pituitary GnRH receptor and, with continuous implant-delivered exposure, causes GnRHR desensitization and downregulation. LH and FSH secretion is suppressed, leading to sustained reduction of testosterone to castrate levels in men and estradiol to prepubertal levels in children with CPP. The flare phase typically occurs in the first week and resolves as receptor density decreases.

The hydrogel implant releases approximately 50 to 65 mcg of histrelin per day for at least 12 months before requiring removal and potential replacement.

Research Summary

Pharmacokinetics

Steady-state serum histrelin concentrations of roughly 0.4 to 0.6 ng/mL are achieved within days of implant insertion and maintained for 12 months. Testosterone suppression to less than 50 ng/dL is typically achieved within 4 weeks. Elimination involves peptidase hydrolysis with renal and biliary clearance of fragments. The depot design minimizes peak-trough variability compared with injection-based GnRH agonists.

Dosing Protocols

• Prostate cancer (Vantas): One 50 mg subcutaneous implant annually, inserted in the inner upper arm under local anesthesia
• Central precocious puberty (Supprelin LA): One 50 mg subcutaneous implant annually
• Implant removal: Required at or before 12 months; a new implant may be placed in the opposite arm

Baseline and periodic testosterone or LH/FSH and estradiol levels are monitored to confirm suppression.

Common Discussion Topics

• Difficulty of implant removal after prolonged implantation (fibrous encapsulation)
• Bone mineral density management in pediatric CPP patients on multi-year therapy
• Use in gender-affirming care for adolescents as a reversible puberty blocker
• Comparison with monthly leuprolide depot from an adherence standpoint
• Cost, insurance coverage, and minor procedure logistics for annual replacement

Related Compounds

• Leuprolide — depot GnRH agonist
• Buserelin — GnRH agonist
• Triptorelin — depot GnRH agonist
• Nafarelin — intranasal GnRH agonist
• Degarelix — GnRH antagonist
• Gonadorelin — native GnRH