Products
Tamsulosin is commercially available in the form of sustained-release tablets and sustained-release capsules and has been approved in many countries since 1996 (Pradif, Pradif T, generics). Tamsulosin is also available as a fixed combination with the 5alpha-reductase inhibitor dutasteride (Duodart), see under dutasteride tamsulosin. In 1996, sustained-release capsules were released (Pradif). Pradif T sustained-release tablets were not approved until 2005. In this form, it is also referred to as “tamsulosin T.”
Structure and properties
Tamsulosin (C20H28N2O5S, Mr = 408.51 g/mol) is present in drugs as tamsulosin hydrochloride, a white crystalline powder that is sparingly soluble in water. Only the -(-)-isomer is used clinically. Tamsulosin is a methoxybenzenesulfonamide and is not one of the quinazoline derivatives such as terazosin and alfuzosin.
Effects
Tamsulosin (ATC G04CA02) binds competitively to postsynaptic α1-adrenoreceptors as an antagonist, relaxing prostatic and urethral smooth muscle. This increases urinary flow, improves urination and filling symptoms. Due to selectivity for the α1A receptor (urinary tract) over the α1B receptor (vasculature), fewer cardiovascular side effects are reported to occur than with other alpha blockers. The effects occur rapidly, within hours to days, compared with 5alpha-reductase inhibitors. Tamsulosin has no effect on prostate size; it is effective only against symptoms.
Indications
For the treatment of functional symptoms of benign prostatic enlargement.
Contraindications
- Hypersensitivity
- Orthostatic hypotension in the patient history.
- Severe hepatic insufficiency
Full precautions can be found in the drug label.
Interactions
Tamsulosin is metabolized primarily by CYP3A4 and less so by CYP2D6. Drugs that lower blood pressure (antihypertensives), such as other alpha blockers, may result in increased blood pressure lowering. Interactions are further possible with cimetidine, furosemide, and warfarin.
Adverse effects
The most common adverse effect is dizziness. Occasionally, blood pressure may be lowered, resulting in palpable heartbeats, weakness, orthostatic hypotension, and rarely, brief loss of consciousness. Other side effects include headache, inflammation of the nasal mucosa, constipation, diarrhea, nausea, vomiting, skin rash, pruritus, urticaria, angioedema, abnormal ejaculation, and painful permanent erection of the penis. Cases of intraoperative floppy iris syndrome have been reported. This is a rare complication that can occur during cataract surgery (Leibovici et al, 2009).
