Pharmacology of the HPG Axis and Hormonal Therapies

GnRH Agonist

Drugs that stimulate the release of gonadotropins (LH and FSH) from the pituitary gland.

Leuprolide

A GnRH agonist used for ovulation stimulation, IVF, and treatment of prostate cancer.

GnRH Antagonists

Drugs that block GnRH receptors to decrease FSH/LH and block ovulation.

Degarelix

A GnRH antagonist used for the treatment of advanced prostate cancer.

Estrogen Agonists

Drugs that mimic the effects of estrogen in the body.

Ethinyl Estradiol

An estrogen agonist used in oral contraceptives.

SERMs

Selective Estrogen Receptor Modifiers that increase effects in some tissues and decrease in others.

Clomiphene

A SERM that selectively blocks estrogen receptors in the pituitary to increase FSH/LH release.

Tamoxifen

A SERM used for the treatment and prevention of ER+ breast cancer.

SERD

Selective Estrogen Receptor Downregulators that act as antagonists in all tissues.

Fulvestrant

A SERD used for tamoxifen-resistant breast cancer.

Aromatase Inhibitors

Drugs that inhibit the aromatase enzyme, blocking the conversion of androgens to estrogens.

Anastrozole

An aromatase inhibitor used in the treatment of breast cancer.

Androgen Agonist

Drugs that mimic the effects of androgens in the body.

Testosterone

The primary male sex hormone responsible for the development of male characteristics.

5 alpha reductase Inhibitor

Drugs that inhibit the conversion of testosterone to dihydrotestosterone (DHT).

Finasteride

A 5 alpha reductase inhibitor used for benign prostatic hyperplasia and male pattern baldness.

Androgen receptor Antagonist

Drugs that block the action of androgens at their receptor sites.

Bicalutamide

An androgen receptor antagonist used in prostate cancer treatment.

Androgen and Aldosterone Antagonist

Drugs that block the effects of androgens and aldosterone.

Spironolactone

An antagonist that increases the conversion of testosterone to estradiol.

Eplerenone

An aldosterone antagonist used primarily for hypertension.

Pulsatile GnRH

GnRH released in pulses that stimulates the production of LH and FSH.

Continuous GnRH

GnRH given continuously that initially increases LH/FSH but eventually decreases them.

Estrogen Effects

Includes development of female sex characteristics, endometrial proliferation, and prothrombotic effects.

Oral Hormonal Contraception

Combination of estrogen and progestin to prevent ovulation and alter endometrial changes.

Emergency contraception

Levonorgestrel 1.5 mg (Plan B) must be taken within 72 hours of unprotected sex.

Drug Inducers

Substances that increase hepatic clearance of hormonal contraceptives.

Contraindications for Estrogen

Includes history of DVT, recent MI/CVA, breast/endometrial cancer, and pregnancy.