Tamsulosin
Tamsulosin hydrochloride
Also known as: Flomax relief · Flomaxtra · Tamsulosinum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Dosing by species
Dosing data for this drug is not yet available in the VetSheet formulary. Every other section below is complete. Consult the current product label before prescribing.
Overview
Tamsulosin is an alpha-1 adrenergic antagonist with high selectivity for the urinary tract. It works by relaxing the smooth muscle in the prostate, urethra, and bladder neck, thereby aiding urine flow. It has a longer duration of action compared to other alpha-blockers like prazosin or phenoxybenzamine.
Clinical Pearl: In veterinary medicine, tamsulosin is frequently used off-label to manage functional urinary retention, benign prostatic hyperplasia (BPH) in intact male dogs, and to facilitate the medical expulsive therapy of ureteroliths or uroliths.
Mechanism of action
Tamsulosin selectively binds to and blocks alpha-1A and alpha-1D adrenergic receptors located predominantly in the smooth muscle of the prostate, prostatic capsule, prostatic urethra, and bladder neck.
Blockade of these receptors → relaxation of smooth muscle → decreased urethral resistance → improved urine flow and relief of functional urinary obstruction.
Safety & warnings
Contraindications
- Hypersensitivity to tamsulosin
- Severe hepatic impairment
- History of orthostatic hypotension
Adverse effects
- Hypotension
- Lethargy
- Weakness
- Gastrointestinal upset (vomiting, diarrhea)
- Dizziness
Precautions
Caution: May cause hypotension. Monitor blood pressure, especially when initiating therapy or combining with other hypotensive agents. Use with caution in patients with renal or hepatic impairment.
Drug interactions
Additive hypotensive effects
Increased risk of hypotension
Decreased clearance of tamsulosin, potentially increasing plasma concentrations
Monitoring
- Urine output and ease of urination
- Blood pressure
- Renal function
Pharmacokinetics
Absorption
Well absorbed from the gastrointestinal tract; absorption may be affected by food.
Distribution
Highly bound to plasma proteins.
Metabolism
Metabolized in the liver via cytochrome P450 enzymes.
Elimination
Excreted primarily in the urine as metabolites and some unchanged drug.
Overdose
Overdosage may lead to severe hypotension. Treatment is primarily supportive, including intravenous fluid therapy and potentially vasopressors if hypotension is refractory. Emesis or gastric lavage may be considered if ingestion is recent.
Available products
Formulations
- 0.4 mg tablets
- 0.4 mg capsules
Human-labeled
- Flomax relief 0.4 mg capsules
- Flomaxtra 0.4 mg tablets
Regulatory status
Approved for human use; used off-label in veterinary medicine under the cascade.
Available as POM (Prescription Only Medicine) and P (Pharmacy) for human use; used off-label in veterinary medicine.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store at room temperature, away from moisture and heat.
Client information
Give this medication exactly as prescribed by your veterinarian.
- Do not crush or chew the capsules or tablets unless specifically instructed, as they are often formulated for modified release.
- Monitor your pet's urination to ensure they are passing urine comfortably and in adequate amounts.
- Watch for signs of weakness, lethargy, or fainting, which could indicate low blood pressure.
- Always provide access to fresh water.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.