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Phenoxybenzamine

Prescription
Alpha-adrenergic blocker (irreversible, non-selective)
Last reviewed 19 Apr 2026 · PetCare.AI Editorial Team
Species
Dog, Cat
Brands
2 available
Interactions
1 documented
Formulations
1

Mechanism of action

Irreversibly blocks alpha-1 and alpha-2 adrenergic receptors, relaxing smooth muscle in the urethral sphincter and prostate

At a glance

Class
Alpha-adrenergic blocker (irreversible, non-selective)
Schedule
Prescription
Storage
Store below 25°C, protect from light

Dosing

🐕

Dog

Functional urethral obstruction / Urethral sphincter hypertonus
Dose
0.25–0.5 mg/kg
Route
PO
Frequency
BID to TID
Max dose
20 mg/dose; 40 mg/day
Duration: Short- to medium-term; onset 24–48h
🐈

Cat

Feline urethral obstruction (post-unblocking) / Urethral spasm
Dose
0.25–0.5 mg/kg
Route
PO
Frequency
BID
Max dose
5 mg/dose; 10 mg/day
Duration: 5–14 days post-catheter removal

Formulations

💊

Capsule — 1

Strength
10mg
Available in India

Storage

Store below 25°C, protect from light

Safety

Absolute contraindications — do not use

  • Hypotension

Use with caution

  • Cardiac disease
    May cause reflex tachycardia

Adverse effects

Common
Hypotension
Tachycardia
Miosis
Nasal congestion
Serious
Severe hypotension
Syncope

Monitoring parameters

Blood pressureHeart rateUrination pattern

Interactions

Major — 1

Acepromazine
major
Both are alpha-adrenergic blockers; combined use may cause severe refractory hypotension
Management: Avoid concurrent use. If sedation needed, use alternative sedative (trazodone, gabapentin).

Brands

International

Dibenzyline
Concordia

India

Fenoxene
Samarth Pharma

FAQs

Frequently asked questions

›What is Phenoxybenzamine?
Phenoxybenzamine is a alpha-adrenergic blocker (irreversible, non-selective) used in pets. Irreversibly blocks alpha-1 and alpha-2 adrenergic receptors, relaxing smooth muscle in the urethral sphincter and prostate
›What is Phenoxybenzamine used for in pets?
Phenoxybenzamine is used in veterinary medicine for: Functional urethral obstruction / Urethral sphincter hypertonus; Feline urethral obstruction (post-unblocking) / Urethral spasm.
›What is the Phenoxybenzamine dose for dogs?
For dogs, Phenoxybenzamine is typically dosed as follows — Functional urethral obstruction / Urethral sphincter hypertonus: 0.25–0.5 mg/kg PO BID to TID. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Phenoxybenzamine dose for cats?
For cats, Phenoxybenzamine is typically dosed as follows — Feline urethral obstruction (post-unblocking) / Urethral spasm: 0.25–0.5 mg/kg PO BID. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What are the side effects of Phenoxybenzamine?
Common: Hypotension, Tachycardia, Miosis, Nasal congestion. Serious (call your vet immediately): Severe hypotension, Syncope.
›Does Phenoxybenzamine need a prescription?
Yes. Phenoxybenzamine is a prescription medication and should only be administered under veterinary supervision.
›When should Phenoxybenzamine not be used?
Do not use Phenoxybenzamine if: Hypotension.

References

References

Textbooks & handbooks

  • Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
  • Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
  • Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
  • National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
  • The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/

Clinical guidelines & consensus

  • Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
  • American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.

Journals & peer-reviewed studies

  • Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
  • Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
  • ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control

Regulatory & approvals

  • Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/

Databases

  • Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →