Phenoxybenzamine
Also known as: Dibenzyline, Dibenyline
Phenoxybenzamine is often prescribed to help your pet urinate more easily by relaxing the muscles of the urinary tract, or to manage high blood pressure associated with certain adrenal tumors. - **Patience is key**: It may take a week or longer to see the full effect on your pet's urination. Do not stop the medication early unless directed by your veterinarian. - **Give with food**: Administering this medication with meals can help reduce stomach upset (nausea or vomiting). - **Watch for low blood pressure**: Because this drug relaxes blood vessels, it can cause a drop in blood pressure. Contact your veterinarian immediately if your pet appears weak, dizzy, or collapses, especially after standing up. - **Missed doses**: If you miss a dose, give it as soon as you remember, but never give two doses at once.
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
What it is used for
- Functional urethral obstruction
- Functional urethral obstruction
- Functional urethral obstruction
- Short-term treatment of hypertension
- Short-term treatment of hypertension
- Short-term treatment of hypertension
- Decrease urethral sphincter tone in bladder paresis
- Adjunctive treatment of laminitis (developmental phase)
- Treatment of profuse, watery diarrhea
- Functional urethral obstruction
- Functional urethral obstruction
- Functional urethral obstruction
- Functional urethral obstruction
How it is given
Possible side effects
- Hypotension (postural/orthostatic)
- Hypertension (rebound)
- Miosis
- Increased intraocular pressure
- Tachycardia (reflex)
- Sodium retention
- Inhibition of ejaculation
- Nasal congestion
- Weakness or dizziness
- Gastrointestinal effects (nausea, vomiting)
- Constipation (specifically noted in horses)
- Hypotension
- Tachycardia
Cautions & contraindications
- Conditions where hypotension is undesirable (e.g., shock, unless fluid replacement is adequate)
- Horses with clinical signs of colic
- Glaucoma (relative contraindication)
- Diabetes mellitus (relative contraindication)
- Use with extreme caution in patients with **congestive heart failure (CHF)** or other heart disease, as drug-induced tachycardia can occur. Use cautiously in patients with renal damage or cerebral/coronary arteriosclerosis. **Pregnancy**: FDA Category C. Animal studies (guinea pigs) have shown abnormalities in the closure of the patent ductus. Use only if benefits outweigh risks.
Drug interactions
- Epinephrine: Epinephrine reversal: If used with drugs that have both alpha- and beta-adrenergic effects, increased hypotension, vasodilation, or tachycardia may result due to unopposed beta effects.
- Phenylephrine: Phenoxybenzamine will antagonize the effects of alpha-adrenergic sympathomimetic agents.
- Reserpine: Phenoxybenzamine can antagonize the hypothermic effects of reserpine.
- Beta-blockers: Increased risk of first dose hypotensive effect; if used for phaeochromocytoma, beta-blockers must only be started after alpha blockade is in place to avoid hypertensive crisis.
- Diuretics: Increased risk of first dose hypotensive effect.
- Alpha-adrenergic sympathomimetics (e.g., phenylephrine): Phenoxybenzamine will antagonize the effects of these agents.
Frequently asked questions
What is Phenoxybenzamine used for in pets?
Phenoxybenzamine is often prescribed to help your pet urinate more easily by relaxing the muscles of the urinary tract, or to manage high blood pressure associated with certain adrenal tumors. - **Patience is key**: It may take a week or longer to see the full effect on your pet's urination. Do not stop the medication early unless directed by your veterinarian. - **Give with food**: Administering this medication with meals can help reduce stomach upset (nausea or vomiting). - **Watch for low blood pressure**: Because this drug relaxes blood vessels, it can cause a drop in blood pressure. Contact your veterinarian immediately if your pet appears weak, dizzy, or collapses, especially after standing up. - **Missed doses**: If you miss a dose, give it as soon as you remember, but never give two doses at once.
Is Phenoxybenzamine safe for my pet?
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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