Tamsulosin is a selective antagonist at alpha-1A and alpha-1B-adrenoceptors in the prostate, prostatic capsule, prostatic urethra, and bladder neck. At least three discrete alpha1-adrenoceptor subtypes have been identified: alpha-1A, alpha-1B, and alpha-1D; their distribution differs between human organs and tissue. Approximately 70% of the alpha1-receptors in human prostate are of the alpha-1A subtype. Blockage of these receptors causes relaxation of smooth muscles in the bladder neck and prostate.
Tamsulosin is a selective antagonist at alpha-1A and alpha-1B-adrenoceptors in the prostate, prostatic capsule, prostatic urethra, and bladder neck. At least three discrete alpha1-adrenoceptor subtypes have been identified: alpha-1A, alpha-1B and alpha-1D; their distribution differs between human organs and tissue. Approximately 70% of the alpha1-receptors in human prostate are of the alpha-1A subtype. Blockage of these receptors causes relaxation of smooth muscles in the bladder neck and prostate
Mechanism of Action of Tamsulosin
Tamsulosin is a selective antagonist at alpha-1A and alpha-1B-adrenoceptors in the prostate, prostatic capsule, prostatic urethra, and bladder neck. At least three discrete alpha1-adrenoceptor subtypes have been identified: alpha-1A, alpha-1B, and alpha-1D; their distribution differs between human organs and tissue. Approximately 70% of the alpha1-receptors in human prostate are of the alpha-1A subtype. Blockage of these receptors causes relaxation of smooth muscles in the bladder neck and prostate, and thus decreases urinary outflow resistance in men. Studies show that tamsulosin has about 12 times greater affinity for alpha-1 adrenergic receptors in the prostate than those in the aorta, which may result in a reduced incidence of adverse cardiovascular effects.
Indications of Tamsulosin
- Benign Prostatic Hyperplasia
- Urinary Tract Stones
- Overactive Bladder
- Bladder Outlet Obstruction
- Ureteral Calculus
- Treatment for acute urinary retention.
- Used in the treatment of signs and symptoms of benign prostatic hyperplasia (reduction in urinary obstruction and relief of associated manifestations such as hesitancy, terminal dribbling of urine, interrupted or weak stream
Contra-Indications of Tamsulosin
- Blood Pressure Drop Upon Standing
- Continued Painful Erection
- Cataract Surgery
- Intraoperative Floppy Iris Syndrome
- CYP2D6 Poor Metabolizer
- Reduced Activity of Cytochrome p450 CYP3A4
- Allergies to tamsulosin
Dosages of tamsulosin
- Strengths: 0.4 mg
Benign Prostatic Hyperplasia
Initial Dose
- 0.4 mg orally once a day
Maximum Dose
- 0.8 mg orally once a day
For patients who do not respond to the 0.4 mg dose after 2 to 4 weeks, the dose may be increased to 0.8 mg orally once a day
Side Effects of Tamsulosin
The most common
- a headache
- dizziness
- a runny nose
- diarrhea
- a cough
- a sore throat or trouble swallowing
- back or chest pain
- A cough or hoarseness
- fever or chills
- lower back or side pain
- painful or difficult urination
Less common
- Chest pain
- abnormal ejaculation
- priapism (painful, long-lasting erection)
- blurred vision
- low blood pressure when changing positions that cause you to feel lightheaded, faint, or dizzy
- allergic reaction, with trouble breathing, fever, swelling of your throat or tongue, rash, itching, or hives
Rare
- Dizziness or lightheadedness
- dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
- the feeling of constant movement of self or surroundings
- painful or prolonged erection of the penis
- sensation of spinning
Rare
- Blistering, peeling, or loosening of the skin
- blurred vision
- confusion
- diarrhea
- difficult or labored breathing
- fast, pounding, or irregular heartbeat or pulse
- itching
- joint or muscle pain
Drug Interaction of Tamsulosin
Tamsulosin hydrochloride may interact with following drugs, supplements & change the efficacy of drugs
- alpha/beta agonists (e.g., epinephrine, norepinephrine)
- alpha agonists (e.g., clonidine, methyldopa)
- other alpha-blockers (e.g., alfuzosin, doxazosin, prazosin)
- “azole” antifungals (e.g., fluconazole, itraconazole, ketoconazole)
- barbiturates (e.g., phenobarbital, pentobarbital)
- beta-adrenergic blockers (e.g., atenolol, propranolol, sotalol)
- calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
- carbamazepine
- cimetidine
- cyclosporine
- desipramine
- dexamethasone
- haloperidol
- macrolide antibiotics (e.g., clarithromycin, erythromycin, telithromycin)
- medications for erectile dysfunction (e.g., sildenafil, tadalafil, vardenafil)
- metronidazole
- monoamine oxidase inhibitors (MAOIs; e.g.,, phenelzine, rasagiline, selegiline, )
- oxcarbazepine
- phenytoin
- sertraline
- tetracycline
Pregnancy & Lactation Tamsulosin
FDA Pregnancy Category B
Pregnancy
Tamsulosin is not recommended for women, including pregnant women.
Lactation
Tamsulosin is not recommended for women, in breastfeeding-feeding women.
References
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