Brand name: Flomax
Drug class: Selective alpha-1-Adrenergic Blocking Agents
ATC class: G04CA02
VA class: CV150
Chemical name: (R)-5-[2-[[2-(2-ethoxyphenoxy)ethyl]amino]propyl] -2-methoxybenzenesulfonamide monohydrochloride
Molecular formula: C₂₀H₂₈N₂O₅S•HCl
CAS number: 106463-17-6

Medically reviewed by Drugs.com on May 30, 2023. Written by ASHP.

Introduction

α₁-Adrenergic blocking agent with selectivity for α_1A-adrenergic receptors; sulfamoylphenethylamine derivative.^{1 2 3 5 6 8 9 10 11 12 13 14 15 32 33}

Uses for Tamsulosin

Benign Prostatic Hyperplasia (BPH)

Reduction of urinary obstruction and relief of associated manifestations (e.g., hesitancy, terminal dribbling of urine, interrupted or weak stream, impaired size and force of stream, sensation of incomplete bladder emptying or straining) in hypertensive or normotensive patients with symptomatic BPH.^{1 2 3 5 6 8 9 10 11 12 13 14 15 35}

Although drug therapy usually is not as effective as surgical therapy, it may provide adequate symptomatic relief with fewer and less serious adverse effects compared with surgery.³⁵

May consider combined therapy with an α₁-adrenergic blocker and 5α-reductase inhibitor for men with bothersome moderate to severe BPH and demonstrable prostatic enlargement.³⁵ Has been more effective than therapy with either drug alone in preventing long-term BPH symptom progression.³⁵ Men at risk for BPH progression are most likely to benefit from combination therapy.³⁵

Other Uses

Manufacturer states that tamsulosin should not be used for the treatment of hypertension.¹

Related/similar drugs

finasteride, tadalafil, Flomax, prazosin, Cialis, doxazosin

Tamsulosin Dosage and Administration

Administration

Oral Administration

Administer orally once daily, 30 minutes after the same meal each day.^{1 8}

Swallow capsules intact; do not open, crush, or chew capsules.¹

Dosage

Available as tamsulosin hydrochloride; dosage expressed in terms of the salt.¹

Adults

BPH

Oral

Initially, 0.4 mg once daily.¹ Allow 2–4 weeks to assess response at initial dosage.¹ May increase dosage to 0.8 mg once daily, if necessary, to improve urinary flow rates and reduce symptoms.¹

If administration is interrupted for several days at either dosage (i.e., 0.4 or 0.8 mg daily), reinitiate therapy at dosage of 0.4 mg once daily.¹

Special Populations

Hepatic Impairment

Dosage adjustment not necessary in patients with moderate hepatic impairment.¹

Renal Impairment

Dosage adjustment not necessary in patients with mild to severe renal impairment (Cl_cr 10–70 mL/minute per 1.73 m²).¹

Not studied in patients with end-stage renal disease (Cl_cr <10 mL/minute per 1.73 m²).¹

Cautions for Tamsulosin

Contraindications

• Known hypersensitivity to tamsulosin or any ingredient in the formulation.¹

Warnings/Precautions

Warnings

Postural Hypotension

Potential for postural hypotension, dizziness, or vertigo; syncope may occur.¹

Priapism

Priapism reported rarely; treat promptly.¹

Sensitivity Reactions

Allergic Reactions

Rash, pruritus, urticaria, and angioedema of the tongue, lips, and face reported; positive rechallenge in some patients.¹

Sulfonamide Sensitivity

Allergic reaction to tamsulosin reported rarely in patients with sulfonamide sensitivity.¹ Use with caution in patients with serious or life-threatening sulfonamide sensitivity.¹

General Precautions

Prostate Cancer

Exclude possibility of prostate cancer prior to initiation of therapy.¹

Intraoperative Floppy Iris Syndrome (IFIS)

IFIS observed during phacoemulsification cataract surgery in some patients receiving α₁-blockers, including tamsulosin.^{1 36} Most cases were in patients who continued tamsulosin therapy at the time of cataract surgery.^{1 36}

Specifically question male patients being considered for cataract surgery to ascertain whether they have received tamsulosin or other α₁-blockers.³⁶ If patient has received tamsulosin, ophthalmologist should be prepared for possible modifications to his/her surgical technique (e.g., use of iris hooks, iris dilator rings, viscoelastic substances) to minimize complications of IFIS.^{1 36}

Benefit of discontinuing α₁-blockers, including tamsulosin, prior to cataract surgery not established.^{1 36}

Specific Populations

Pregnancy

Category B.¹ Not indicated for use in women.¹

Lactation

Not indicated for use in women.¹

Pediatric Use

Not indicated for use in children.¹

Geriatric Use

No substantial differences in safety and efficacy relative to younger adults, but increased sensitivity cannot be ruled out.¹

Common Adverse Effects

Headache, infection, asthenia, back pain, chest pain, dizziness, somnolence, insomnia, decreased libido, rhinitis, pharyngitis, increased cough, sinusitis, diarrhea, nausea, tooth disorder, abnormal ejaculation, blurred vision.¹

Drug Interactions

Specific Drugs

Tamsulosin Pharmacokinetics

Absorption

Bioavailability

Essentially completely absorbed following oral administration under fasting conditions; peak plasma concentrations attained within 4–5 hours.¹

Food

Food delays time to peak plasma concentration by about 2 hours.¹ When administered under fasting conditions, bioavailability and peak plasma concentration are increased by 30 and 40–70%, respectively, compared with fed state.¹

Distribution

Extent

Appears to distribute into extracellular fluids in humans.¹ In animals, distributed into kidney, prostate, liver, gallbladder, heart, aorta, and brown fat, with minimal distribution into brain, spinal cord, and testes.¹

Plasma Protein Binding

94–99% (mainly to α₁-acid glycoprotein).¹

Special Populations

In patients with moderate hepatic impairment, protein binding is altered, resulting in changes in overall plasma concentrations; however, no substantial alterations in intrinsic clearance and concentrations of unbound drug.^{1 8 13}

In patients with renal impairment, protein binding is altered, resulting in changes in overall plasma concentrations; however, no substantial alterations in intrinsic clearance and concentrations of unbound drug.^{1 8 13}

Elimination

Metabolism

Extensively metabolized by CYP enzymes (specific isoenzyme[s] not identified) in the liver.¹ Metabolites undergo further conjugation prior to excretion.¹

Elimination Route

Excreted in urine (76%) and feces (21%).¹

Half-life

Because of absorption rate-controlled pharmacokinetics of tamsulosin capsules, apparent half-life is about 9–13 hours in healthy individuals and 14–15 hours in patients with BPH.¹

Special Populations

In males 55–75 years of age, intrinsic clearance is decreased and elimination half-life is prolonged, resulting in a 40% increase in AUC compared with males 20–32 years of age.^{1 34}

Stability

Storage

Oral

Capsules

25°C (may be exposed to 15–30°C).¹

Actions

• Binds to α₁-adrenergic receptors on the prostate and the bladder trigone, resulting in decreased urinary outflow resistance in men.^{2 5 8 9 11 12}

• Higher affinity for α_1A-adrenergic receptors, which are located in nonvascular smooth muscle (e.g., prostate), than for α_1B-adrenergic receptors located in vascular smooth muscle (e.g., internal iliac artery);^{1 8 9 10 11 12 33} may result in reduced incidence of cardiovascular effects (e.g., syncope, dizziness, hypotension).^{8 9 10 11 12 13}

Advice to Patients

• Importance of providing patient a copy of manufacturer’s patient information and advising patient to read and follow instructions for use.¹

• Risk of feeling faint or dizzy, particularly following initiation of therapy or dosage increase; avoid operating machinery or driving a motor vehicle for 12 hours following initial dose or dosage increase.¹

• Importance of sitting or lying down when symptoms of lowered BP occur and of rising carefully from a sitting or lying position.¹

• Importance of advising male patients being considered for cataract surgery that they should inform their ophthalmologist of current or prior α₁-blocker therapy.¹

• Importance of men seeking medical treatment promptly if an erection is painful or persists for several hours.¹

• Importance of taking tamsulosin 30 minutes after the same meal each day.¹ Importance of swallowing the capsules whole and of not chewing, crushing, or opening the capsules.¹

• Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs.¹

• Importance of informing patients of other important precautionary information.¹ (See Cautions.)

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

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