Tamsulosin

Tamsulosin is an alpha 1A and alpha 1D selective blocker used for lower urinary tract symptoms from benign prostatic hyperplasia. Its selectivity for prostatic receptors gives less blood pressure lowering than non selective alpha blockers. It is not an antihypertensive.

Classification. Selective alpha 1A and alpha 1D antagonist; sulphonamide derivative.

Mechanism. Relaxes smooth muscle of the prostate, bladder neck and urethra, and lowers outlet resistance. Alpha 1D blockade in the bladder may help storage symptoms.

Pharmacodynamics. Improvement in flow rate and symptoms within 1 to 2 weeks, with full effect after about 4 weeks. Orthostatic hypotension is less frequent than with prazosin.

Pharmacokinetics. Modified release absorption is slowed and increased by food; take after the same meal each day. Half life about 9 to 13 hours. Metabolised by CYP3A4 and CYP2D6; mostly renal excretion of metabolites.

Benign prostatic hyperplasia, adult men.

• Tamsulosin 400 micrograms orally once daily, 30 minutes after the same meal each day.

• Some markets allow 800 micrograms daily if there is no response after 2 to 4 weeks; benefit of the higher dose is small.

• Review response at 4 to 6 weeks; continue as long as symptoms benefit.

Medical expulsive therapy for ureteric stones (off label). 400 micrograms once daily for up to 4 weeks for distal stones of about 5 to 10 mm; evidence for benefit is mixed and strongest for larger stones. Combine with analgesia and review for failure or infection.

Women and children. Not licensed; occasionally used off label for voiding dysfunction under specialist direction.

Acute retention. Start 400 micrograms daily at catheterisation before catheter removal (alpha blocker assisted voiding), continuing for at least 2 days before the attempt.

Contraindications. Hypersensitivity; history of orthostatic hypotension; severe liver impairment.

Warnings. Orthostatic hypotension and syncope, especially on starting. Intraoperative floppy iris syndrome: tell the eye surgeon before cataract surgery, and avoid starting before cataract surgery. Priapism, rarely. Rare cross reaction in severe sulphonamide allergy. Exclude prostate cancer before treatment of symptoms.

Adverse effects. Dizziness, retrograde or abnormal ejaculation, rhinitis, headache, asthenia, back pain, palpitations, postural hypotension.

Interactions. Strong CYP3A4 inhibitors (ketoconazole, ritonavir) and CYP2D6 inhibitors (paroxetine, fluoxetine): raise levels; avoid combination with a strong CYP3A4 inhibitor. Other alpha blockers: avoid. Phosphodiesterase 5 inhibitors: hypotension. Cimetidine raises exposure.

Special groups.

• Pregnancy and breastfeeding: not applicable to the licensed use.

• Older adults: monitor for postural hypotension and falls.

• Kidney impairment: no adjustment down to eGFR 10 mL/min; under 10 mL/min use caution.

• Liver impairment: mild to moderate: no adjustment; severe: not studied, avoid.

Formulations. Modified release capsules 400 micrograms; combination with dutasteride in some markets.

Administration. Swallow whole; do not crush or chew. Take 30 minutes after the same meal each day; fasting administration changes exposure.

Baseline. International prostate symptom score, flow rate and residual volume if available, digital rectal examination, prostate specific antigen as indicated, eye history.

Monitoring. Symptom score at 4 to 6 weeks and then every 6 to 12 months; sitting and standing pressure; ejaculatory complaints; review need if no benefit by 3 months.

Stopping. Stop if there is no benefit, if intolerable dizziness occurs, or before cataract surgery after discussion with the surgeon.

Common prescribing errors. Prescribing it for hypertension; combining with another alpha blocker; omitting the eye surgery warning; crushing the capsule.