Pharmacokinetic considerations for gonadotropin-releasing hormone agonists and antagonists to treat endometriosis

Anna Maria Paoletti, Paoletti AM, Manuela Neri, Monica Pilloni, Pilloni M, Maria Francesca Marotto, Marotto MF, Elena Giancane, Giancane E, Valerio Vallerino, Bruno Piras, Piras B, Melis G, Giulia Melis, Virginia Melis, Melis V, Masciale MDM, Michele Danilo Maria Masciale, E. Murgia, Enrica Murgia, Murgia E, Melis GB, Gian Benedetto Melis
Expert opinion on drug metabolism & toxicology · 2025 · vol. 21(6) , pp. 649–663 · doi:10.1080/17425255.2025.2499550 · PMID:40315284 · W4410027033
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⚙ AI-generated summary by claude@2026-06, 2026-06-08 ⓘ

This review discusses the pharmacokinetic properties of GnRH agonists and antagonists, highlighting that non-peptide GnRH antagonists offer faster action and oral administration for endometriosis treatment.

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⚙ AI-generated deep summary by claude@2026-07, 2026-07-16 · read from full text ⓘ

This manuscript reviews pharmacological and pharmacokinetic considerations for GnRH agonists and antagonists used to induce hypoestrogenism as a strategy for treating endometriosis, synthesizing evidence from an electronic literature search and discussing routes of administration. It reports that GnRH agonists suppress estradiol and gonadotropins after about 10–12 days but initially can cause a flare-up due to early stimulation, whereas peptide GnRH antagonists act quickly to block GnRH receptors yet are limited by peptide-related administration complexity, and non-peptide GnRH antagonists can be taken orally and produce rapid, dose-dependent hypoestrogenism with reversibility. A major caveat emphasized is that hypoestrogenism-related side effects—particularly those affecting bone and quality of life—require add-back therapy with estrogen and progestin, and that complex administration schedules are a disadvantage for agonists and peptide antagonists. This paper is centrally about endometriosis — it focuses on pharmacokinetic features of GnRH analogs (including agonists and peptide/non-peptide antagonists) and how these properties relate to achieving hypoestrogenism for endometriosis treatment.

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Abstract

INTRODUCTION: Endometriosis is a chronic disease characterized by endometriotic cells implanted outside the uterus triggering a chronic inflammatory state. Estradiol stimulates the endometriotic implants, which overexpress estrogen receptor β. Lowering estradiol levels to a range within 40-50 pg/ml allows antagonizing the growth of endometriotic implants and counteracting its-related disabling symptoms. AREAS COVERED: By blocking the Gonadotropin-Releasing-Hormone (GnRH) receptors, GnRHagonists, peptide GnRHantagonists, non-peptide GnRHantagonists induce hypoestrogenism, due to the suppression of pituitary gonadotropins. This manuscript provides the results of an electronic literature search on pharmacological features of GnRHagonists and GnRHantagonists to treat endometriosis. Hypoestrogenism-dependent side effects can be counteracted by concomitant estrogen and progestin compounds (add-back therapy). GnRHagonists chronic administration induces hypoestrogenism after 10-12 days, since initial administrations stimulate gonadotropin rise (flare-up effect). Peptide GnRHantagonists quickly block GnRH-receptors inducing an immediate hypoestrogenism. Similarly to GnRHagonists, their peptide structure impedes the oral administration. The non-peptide GnRHantagonists have the advantage both of being taken orally and inducing a rapid dose-dependent hypoestrogenism. EXPERT OPINION: GnRHagonists and peptide GnRHantagonists are effective to treat endometriosis, but require complex ways of administration. Non-peptide GnRHantagonists offer more important prospects in the tailored medical treatment of endometriosis, given their rapid onset of action and their oral way of administration.
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ABSTRACT Introduction Endometriosis is a chronic disease characterized by endometriotic cells implanted outside the uterus triggering a chronic inflammatory state. Estradiol stimulates the endometriotic implants, which overexpress estrogen receptor β. Lowering estradiol levels to a range within 40–50 pg/ml allows antagonizing the growth of endometriotic implants and counteracting its-related disabling symptoms. Areas covered By blocking the Gonadotropin-Releasing-Hormone (GnRH) receptors, GnRHagonists, peptide GnRHantagonists, non-peptide GnRHantagonists induce hypoestrogenism, due to the suppression of pituitary gonadotropins. This manuscript provides the results of an electronic literature search on pharmacological features of GnRHagonists and GnRHantagonists to treat endometriosis. Hypoestrogenism-dependent side effects can be counteracted by concomitant estrogen and progestin compounds (add-back therapy). GnRHagonists chronic administration induces hypoestrogenism after 10–12 days, since initial administrations stimulate gonadotropin rise (flare-up effect). Peptide GnRHantagonists quickly block GnRH-receptors inducing an immediate hypoestrogenism. Similarly to GnRHagonists, their peptide structure impedes the oral administration. The non-peptide GnRHantagonists have the advantage both of being taken orally and inducing a rapid dose-dependent hypoestrogenism. Expert opinion GnRHagonists and peptide GnRHantagonists are effective to treat endometriosis, but require complex ways of administration. Non-peptide GnRHantagonists offer more important prospects in the tailored medical treatment of endometriosis, given their rapid onset of action and their oral way of administration. Article highlights In women who do not respond to the first-line therapies, endometriosis can be treated by inducing hypoestrogenism with the GnRHanalogs. However, this therapeutical strategy shows some disadvantages: non-immediate suppression of gonadotropins and estradiol; complex ways of administrations, such as daily subcutaneous injections, more than one daily intranasal spray, depot intramuscular or subcutaneous injections either every month or every 3–4 months; hypoestrogenism-dependent side effects, disabling the quality of life and the health, especially affecting the bone. However, all of these adverse effects can be antagonized by the concomitant administration of estrogen and progestin (add back therapy). The peptide GnRHantagonists over the GnRHagonists offer the advantage of inducing an immediate suppression of gonadotropins and estradiol, but like the GnRHagonists: require complex ways of administrations. need to counteract the hypoestrogenism side effects with add-back therapy. The discovery of non-peptide GnRHantagonists opens a new scenario in the treatment of endometriosis: immediate suppression of gonadotropins and estradiol. oral administration unlike complex ways of administrations of GnRHagonists and peptide GnRH antagonists. decrease in gonadotropins and estradiol related to doses of the non-peptide GnRH antagonist. rapid reversibility of related-hypoestrogenism. Declaration of interest The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. Reviewer disclosure Peer reviewers on this manuscript have no relevant financial or other relationships to disclose. Acknowledgments The authors thank K Jenkins for revising the English language of the manuscript.

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Condition tags

endometriosis

MeSH descriptors

Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis Endometriosis

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