Extended Use of Histrelin Implant in Pediatric Patients.

Purpose: Histrelin implant (HI) is a gonadotropin-releasing hormone agonist (GnRHa) used in pediatrics to treat central precocious puberty (CPP) and for pubertal suppression in transgender/non-binary (TG/NB) youth with gender dysphoria. HI is designed for annual removal/replacement; however, effectiveness has been reported beyond 1 year. No previous study has assessed prolonged HI use in TG/NB youth. We hypothesize that HI is effective >12 months in TG/NB youth as described in children with CPP.

Methods: This retrospective, two-center study included 49 subjects with 50 HI retained ≥17 months, in TG/NB (42) and CPP (7). Pubertal suppression was assessed biochemically and/or clinically (testicular/breast exams). Escape from pubertal suppression and HI removal is also characterized.

Results: Most implants (42/50) maintained clinical/biochemical suppression for the duration of the study. The average use of a single HI was 37.5±13.6 months. Pubertal suppression escape occurred in eight subjects at average 30.4 months from placement: five had only biochemical; two clinical; and one both clinical and biochemical escape. After an average of 32.9 months, only 3/23 HI removed had adverse effects (HI broken, difficult removal).

Conclusion: Extended use of HI in our TG/NB and CPP subjects was efficacious, resulting in sustained biochemical and clinical pubertal suppression in most. Suppression escape occurred at 15-65 months. Complications at HI removal were infrequent. Keeping HI for extended time would improve cost and morbidity, while maintaining efficacy and safety for most patients.