Tamsulosin hydrochloride

Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.

Flomax (CSL)
400 microgram modified-release capsules
Approved indication: benign prostatic hypertrophy
Australian Medicines Handbook Section 13.2.1

Alpha1 adrenoceptor antagonists, such as prazosin and terazosin, can be used to treat the symptoms of benign prostatic hypertrophy.1 They act by reducing smooth muscle tone in the prostate and bladder neck. Tamsulosin acts in the same way, but is claimed to be more selective for the alpha1 adrenoceptors in the prostate.

The once-daily dose is absorbed slowly. Although food reduces the bioavailability, it is recommended that the dose is taken 30 minutes after breakfast. Most of the drug is metabolised by the liver and the metabolites are excreted in the urine.

In placebo-controlled trials tamsulosin improved the maximum urine flow rates. A comparison of tamsulosin with alfuzosin (a non-selective alpha1 adrenoceptor antagonist), found that both drugs increased maximum flow rate by 1.6 mL/second.2 Similar results were seen in a comparison with terazosin.3

Blocking the alpha1 adrenoceptors reduces the blood pressure, but hypotension is not a frequent problem with tamsulosin. Symptoms, such as dizziness, suggestive of low blood pressure occurred in 9.2% of the tamsulosin group and10.5% of the alfuzosin group.2 In the placebo-controlled studies, the only adverse event which occurred significantly more with tamsulosin was abnormal ejaculation. This affected almost 7% of the men taking tamsulosin.

Overall, tamsulosin is as effective as other drugs in its class, but may have fewer adverse effects. This may be an advantage if tamsulosin does not cost more than its competitors.