Prazosin is an alpha-1 adrenergic antagonist used in feline medicine primarily to relax urethral smooth muscle and reduce urethral spasm in cats with feline lower urinary tract disease (FLUTD) and following relief of urethral obstruction. Urethral obstruction is a life-threatening emergency in male cats, and prazosin plays an important supportive role in post-obstruction management to help prevent re-obstruction.
Overview
Prazosin selectively blocks alpha-1 adrenergic receptors on smooth muscle, including the smooth muscle of the urethra and bladder neck. By relaxing this smooth muscle, prazosin reduces urethral resistance and promotes easier urination. This is particularly valuable in male cats recovering from urethral obstruction, where urethral spasm and inflammation can contribute to re-obstruction. Prazosin also causes vasodilation and can lower blood pressure, which is the basis for its human use as an antihypertensive but represents a potential side effect in cats.
Uses
- Post-urethral obstruction care: Reduces urethral spasm to help prevent re-obstruction after catheter removal.
- Feline lower urinary tract disease (FLUTD): Facilitates urination in cats with functional urethral obstruction or urethral spasm.
- Urinary retention: Used when urethral smooth muscle spasm contributes to difficulty urinating.
- Feline idiopathic cystitis (FIC): May be used as part of multimodal management to ease urethral tone.
Dosage
| Parameter | Detail |
|---|---|
| Dose (cats) | 0.25–0.5 mg per cat orally every 8–12 hours |
| Common formulation | 1 mg capsules (human); compounded suspensions |
| Route | Oral |
| Frequency | Every 8–12 hours |
| Duration | Typically 5–14 days post-obstruction, or as directed |
Important dosing notes:
- Prazosin capsules often need to be compounded into a smaller dose or liquid suspension for cats.
- The first dose may cause a pronounced drop in blood pressure (“first-dose phenomenon”). Monitor your cat closely for signs of weakness, wobbling, or collapse after the first administration.
- Administer with food to reduce the risk of hypotension.
- Do not abruptly discontinue without veterinary guidance.
Side Effects
| Common Side Effects | Serious Side Effects (Contact Your Vet Immediately) |
|---|---|
| Mild lethargy | Severe hypotension (weakness, collapse, rapid heart rate) |
| Decreased appetite | Syncope (fainting) |
| Mild GI upset | Profound lethargy or unresponsiveness |
The most significant concern with prazosin is hypotension. Cats that are already dehydrated or hypovolemic (common after urethral obstruction) are at higher risk.
Drug Interactions
- Other antihypertensives (amlodipine, benazepril, telmisartan): Additive blood pressure lowering effects; risk of significant hypotension.
- Diuretics (furosemide): Potentiate hypotensive effects.
- Acepromazine: Also has alpha-blocking properties; combined use may worsen hypotension.
- NSAIDs: May partially blunt the blood pressure lowering effect.
- Sildenafil: Risk of severe hypotension with concurrent use.
Contraindications
- Do not use in cats with known hypersensitivity to prazosin or other alpha-blockers.
- Use with extreme caution in hypotensive or severely dehydrated cats.
- Avoid in cats with significant cardiac disease where blood pressure is already compromised.
- Safety in pregnant or lactating cats has not been established.
Storage
- Store at room temperature (59–77 degrees F / 15–25 degrees C).
- Keep in a tightly closed container, protected from moisture and light.
- Compounded suspensions may have different storage requirements; follow your pharmacy’s instructions.
- Keep out of reach of children and pets.
FAQ
Q: How long does my cat need to take prazosin after a urethral obstruction? A: Most veterinarians prescribe prazosin for 5 to 14 days following obstruction relief, though the duration varies based on your cat’s clinical progress. Your veterinarian will determine when it is safe to discontinue.
Q: Can prazosin prevent urethral obstruction from happening again? A: Prazosin helps reduce the risk of re-obstruction by relaxing urethral smooth muscle during the recovery period. However, it does not address the underlying causes of obstruction (crystals, mucous plugs, inflammation). Long-term prevention involves dietary management, environmental enrichment, increased water intake, and stress reduction.
Q: My cat seems very sleepy after starting prazosin. Is this normal? A: Mild sedation and lethargy are common, particularly after the first few doses, as the body adjusts to the blood pressure effects. If your cat is severely lethargic, unable to stand, or seems weak, contact your veterinarian, as this may indicate excessive hypotension.
Q: Can female cats take prazosin? A: While urethral obstruction is far more common in male cats due to their narrow urethra, prazosin can be used in female cats with functional urethral disorders if deemed appropriate by a veterinarian.
This content is for informational purposes only and is not a substitute for professional veterinary advice. Always consult your veterinarian before starting, changing, or stopping any medication for your cat.