Estradiol
Estradiol is the principal biologically active endogenous estrogen and is supplied medicinally in several ester formulations. It affects reproductive tissues, sexual behavior and endocrine feedback. Veterinary applications include selected equine reproductive and estrogen-replacement uses. Estradiol cypionate also has a historical background in post-mating pregnancy prevention in small animals.
Group
Estrogen
Mechanism of Action
Estradiol binds intracellular estrogen receptors and changes transcription of estrogen-responsive genes. Effects include proliferation and functional changes in reproductive tissues, alteration of cervical and vaginal secretions, and modulation of sexual receptivity. Feedback on hypothalamic and pituitary signaling changes gonadotropin secretion. Estrogenic effects on urethral tissues and adrenergic responsiveness can also support continence in responsive patients.
Dose Rates
Dog
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Historical pregnancy termination | Reference only | IM | Estradiol cypionate 22–44 mcg/kg once, maximum 1 mg total; timing described as days 3–5 of estrus or within 3 days of mating. Historical regimen, no longer recommended. |
Cat
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Historical pregnancy termination | Reference only | IM | Estradiol cypionate 250 mcg per cat between 40 hours and 5 days after mating. Historical regimen with serious toxicity concerns. |
Horse
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Estrogen-responsive incontinence | Reference only | IM | Estradiol cypionate 4–10 mcg/kg daily for three days, then every other day. Improvement does not establish cure; ester dosing is not interchangeable with estradiol base. | |
| Estrus behavior in ovariectomized mares | Reference only | IM | Estradiol cypionate 5–10 mg once. This ester amount must not be calculated using estradiol-base preparations. |
Indications
- Induction or maintenance of estrous behavior and receptivity in ovariectomized mares used in selected reproductive programs.
- Treatment of selected estrogen-responsive urinary incontinence in mares.
- Selected specialist reproductive protocols in mares, including endocrine support within induced-lactation programs.
Contraindications
- Pregnancy unless termination intended
- Ferrets
- Food-producing animals
- Use without CBC monitoring
Interactions
- Avoid other marrow-suppressing drugs; may increase cyclosporine concentrations.
Adverse effects
- Pyometra and endometrial hyperplasia
- Leukopenia, thrombocytopenia and potentially fatal aplastic anemia
Toxicity
Marrow stem-cell injury may be irreversible.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Estradiol cypionate injection 2 mg/mL | Injection | 2 mg / mL | IM |
| Estradiol valerate injection 20 mg/mL Not interchangeable with cypionate protocols. | Injection | 20 mg / mL | IM |
Monitoring and Administration
Pregnancy-termination use of estradiol cypionate is no longer recommended because of severe adverse effects. Monitor CBC when exposure occurs.
Cypionate and valerate are different esters and must not be substituted by nominal mg concentration.