Urinary incontinence in dogs, particularly in spayed females, can be a distressing condition for both the pet and its owner. While various treatments exist, understanding the role of hormones like diethylstilbestrol and estriol is crucial. These synthetic and natural estrogens, respectively, play a significant role in managing certain types of urinary incontinence by influencing urethral sphincter function. This article delves into the properties, administration, adverse effects, and contraindications of these medications, offering insights for pet owners and veterinary professionals.
Diethylstilbestrol: A Potent Estrogen Derivative
Diethylstilbestrol (DES) is a synthetic nonsteroidal estrogen that closely mimics the natural estrogen estradiol. While once used in human medicine, its use has been largely discontinued due to carcinogenic and teratogenic effects. In veterinary medicine, DES is available through compounding pharmacies in some countries, though it is not commercially available in the US.
Pharmacokinetics and Mechanism of Action
In dogs, diethylstilbestrol is orally bioavailable, reaching peak plasma concentrations within an hour and having an elimination half-life of approximately 24 hours due to enterohepatic recirculation. Its therapeutic effect in managing urinary incontinence stems from its ability to sensitize the urethral sphincter to alpha-adrenergic stimulation. This means it works synergistically with alpha-adrenergic agonists, enhancing their efficacy in preventing urine leakage.
Administration and Adverse Effects
Diethylstilbestrol is typically administered with a daily loading dose for 7 to 10 days, followed by a reduction to once-weekly dosing to minimize the risk of toxic effects. However, dogs treated with DES are susceptible to estrogen-induced bone marrow suppression. This can manifest initially as thrombocytopenia (low platelet count) and, in severe cases, can lead to fatal aplastic anemia. Hematopoietic toxicity is rare in cats.
Other adverse effects in dogs can include alopecia (hair loss), cystic ovaries, cystic endometrial hyperplasia, pyometra (uterine infection), prolonged estrus, and infertility. When administered only once weekly in spayed female dogs, these adverse effects are generally rare. Due to its association with carcinogenicity, DES is banned for use in food animals in most countries, and the FDA prohibits its extralabel use in food-producing animals in the US.
Estriol: A Natural Estrogen for Lower Urinary Tract Health
Estriol is a natural estrogen that exhibits a high affinity for receptors on cells within the lower urogenital tract. In female dogs, estriol is known to increase urethral resting tone. It is approved in the US, Australia, and the UK for treating estrogen-responsive urinary incontinence in ovariohysterectomized (spayed) female dogs.
Absorption and Distribution
After oral administration, estriol is rapidly absorbed and highly protein-bound in plasma. Like other estrogens, it is widely distributed throughout the body, with higher concentrations typically found in sex hormone target organs. Estriol is conjugated in the liver and subsequently excreted in the urine, with an elimination half-life of 8–12 hours in dogs.
Potential Side Effects and Contraindications
While generally considered safer than DES, estriol can still cause adverse effects. These may include anorexia (loss of appetite), emesis (vomiting), polydipsia (excessive thirst), anxiety, aggression, lethargy, hypersalivation, swollen vulvae, estrous behavior, sexual attractiveness, and mammary hyperplasia. These estrogenic effects typically resolve with a reduction in dosage.
Estriol should not be used concurrently with other estrogens. Contraindications for its use include polyuria and polydipsia (frequent urination and thirst), pregnancy, lactation, and in dogs younger than one year of age.
Important Considerations for Owners
When discussing urinary incontinence treatments with your veterinarian, it’s essential to understand the potential benefits and risks associated with medications like diethylstilbestrol and estriol. Your vet will assess your dog’s specific condition, medical history, and overall health to determine the most appropriate and safest treatment plan. Regular monitoring for adverse effects, especially with DES, is crucial for the well-being of your canine companion. The goal is always to improve your dog’s quality of life while minimizing potential health risks.
