Diethylstilbestrol — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	0.1-1 mg/dog (total dose)	q24h for 3-5 days, then once weekly or as needed	Duration: Maintenance: 0.1-1 mg once weekly to monthly Notes: For urinary incontinence, start with 0.5 mg/dog q24h for 3-5 days, then reduce to 0.1-0.5 mg once weekly. Adjust to lowest effective dose.
Dog	IM	0.5-1 mg/dog	Single dose for mismating (historically)	Duration: Once Notes: Use is historical; not recommended due to risk of bone marrow suppression.
Cattle	SC	10-20 mg/animal	Single implant (historically)	Duration: Once Notes: Growth promotion; banned in many countries.

Clinical Indications & Species Uses

General Indications

Estrogen replacement therapy (historically)
Growth promotion in livestock (banned in many regions)

Dog (Canine)

Urethral sphincter mechanism incompetence (USMI) causing urinary incontinence
Estrogen-responsive urinary incontinence
Induction of estrus (historically)

Cattle (Bovine)

Historically used as a growth promoter (banned in many countries)
Treatment of placental retention (historically, but not recommended)

Avian & Poultry

Historically used as a growth promoter (banned in many countries)

Pharmacology & Mechanism of Action

Drug Class: Synthetic Nonsteroidal Estrogen | Pharmacological Group: Estrogens / Hormones

Mechanism of Action: Diethylstilbestrol (DES) is a synthetic nonsteroidal estrogen that binds to estrogen receptors (ERα and ERβ) in target tissues. Upon binding, the receptor-ligand complex translocates to the nucleus and modulates gene transcription, leading to estrogenic effects such as proliferation of the endometrium, development of secondary sexual characteristics, and feedback inhibition of gonadotropin release from the pituitary. In certain tissues, DES can also act as a growth promoter in livestock, increasing protein deposition and feed efficiency.

Pharmacodynamics: DES produces estrogenic effects including uterine growth, vaginal cornification, mammary gland development, and inhibition of pituitary gonadotropin secretion. In dogs, it increases the tone of the urethral sphincter and improves continence in cases of urethral sphincter mechanism incompetence. In livestock, it promotes growth and fattening, but its use as a growth promoter has been banned in many countries due to carcinogenic potential.

⚡ Pharmacokinetics Summary

Absorption: DES is well absorbed after oral administration. It can also be absorbed through the skin and mucous membranes. In animals, oral absorption is rapid, with peak plasma concentrations occurring within 1-2 hours.

Distribution: DES is widely distributed throughout the body, with high concentrations in adipose tissue, liver, and reproductive organs. It crosses the placenta and is excreted in milk.

Metabolism: DES is metabolized primarily in the liver via oxidation and conjugation (glucuronidation and sulfation). It undergoes enterohepatic recirculation, which prolongs its presence in the body.

Excretion: DES and its metabolites are excreted primarily in the urine and feces. Biliary excretion contributes to fecal elimination, and enterohepatic recirculation can delay overall excretion.

Half-Life: The half-life of DES in dogs is approximately 2-3 days; in cattle, it is approximately 4-5 days. However, due to enterohepatic recirculation, the effective half-life may be longer.

Bioavailability: Oral bioavailability is high, estimated at 70-90% in most species, though first-pass metabolism may reduce systemic availability.

Protein Binding: DES is approximately 90% bound to plasma proteins, mainly albumin.

Available Formulations & Strengths

Oral Tablet 0.1 mg, 0.5 mg, 1 mg, 5 mg (PO)

Injectable Solution 5 mg/mL, 25 mg/mL (IM, SC)

Implant (for livestock) 10-20 mg per implant (SC)

Contraindications & Clinical Warnings

Contraindications:

Pregnancy (unless used for abortion)
Animals with estrogen-sensitive tumors (e.g., mammary tumors)
Animals with a history of thromboembolic disease
Animals with hepatic dysfunction
Animals with bone marrow suppression or blood dyscrasias
Use in animals intended for human consumption (banned in many countries)

Warnings & Clinical Precautions:

Use with caution in animals with cardiovascular disease, diabetes mellitus, or hypercalcemia.
Prolonged use may increase the risk of pyometra in intact females.
May cause bone marrow suppression, especially with high doses or prolonged use.
In dogs, DES can cause aplastic anemia; monitor complete blood counts during therapy.
Avoid use in animals with a history of seizures.
In food animals, observe withdrawal times; extra-label use is prohibited in some countries.

Adverse Effects & Reactions

Common:

Nausea and vomiting (especially at high doses)
Mild transient leukopenia
Uterine bleeding or spotting
Vaginal discharge
Increased thirst and urination

Serious / Severe:

Bone marrow suppression (aplastic anemia, leukopenia, thrombocytopenia)
Pyometra in intact females
Endometrial hyperplasia or neoplasia
Thromboembolism
Hepatotoxicity
Carcinogenesis (long-term use)

Rare:

Anaphylaxis
Hypercalcemia
Pancreatitis
Behavioral changes

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Corticosteroids	May increase the risk of hyperglycemia and fluid retention.	Moderate
Warfarin and other anticoagulants	Estrogens may alter anticoagulant effects; increased risk of thrombosis.	High
Phenobarbital and other hepatic enzyme inducers	May increase metabolism of DES, reducing efficacy.	Moderate
Tamoxifen	Competitive antagonism at estrogen receptors, reducing DES effects.	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Severe vomiting and diarrhea
Bone marrow suppression (pancytopenia)
Uterine hemorrhage
Hypercalcemia
Hepatic necrosis
Seizures

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Induce emesis if recent ingestion and the animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids for dehydration and electrolyte imbalances. Monitor complete blood count, serum biochemistry, and coagulation parameters. Blood transfusions may be necessary for severe anemia or thrombocytopenia. For hypercalcemia, administer saline diuresis and consider calcitonin or bisphosphonates. In severe cases, consider bone marrow stimulants (e.g., filgrastim) or referral to a specialist.

Food Animal Withdrawal Times

🥩 Meat: 0 days🥛 Milk: 0 days🥚 Eggs: 0 days

DES is banned for use in food animals in many countries (e.g., EU, USA). Withdrawal times are not established due to prohibition. In countries where it may still be used, a withdrawal period of at least 30 days for meat and 7 days for milk is recommended, but this is not officially recognized.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature, 20-25°C (68-77°F).

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep container tightly closed. Store away from heat and open flames.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use in the US. Withdrawn from market for food animals due to carcinogenicity concerns.

Extra-Label (Off-Label) Use: In the US, DES is not approved for veterinary use; extra-label use is prohibited in food animals under AMDUCA. In companion animals, extra-label use may be permitted with a valid veterinarian-client-patient relationship, but caution is advised due to potential adverse effects.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Diethylstilbestrol is a synthetic estrogen that has been largely replaced by safer alternatives in veterinary medicine. Its primary current use is in dogs for estrogen-responsive urinary incontinence, but even this use is declining due to the availability of safer drugs like phenylpropanolamine (PPA) and estriol. DES is contraindicated in intact females due to the risk of pyometra, and in any animal with a history of estrogen-sensitive tumors. It is a potent bone marrow suppressant, and blood counts should be monitored regularly during therapy. Due to its carcinogenic potential, it is banned for use in food animals in most countries. Veterinarians should consider alternative therapies and use DES only when other options have failed, with careful client education about risks. The drug is not readily available commercially and may need to be obtained from compounding pharmacies.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)