The 5-alpha-reductase inhibitors dutasteride and finasteride are used in benign prostatic hyperplasia to reduce prostate size. They inhibit the enzyme 5-alpha-reductase, which is responsible for converting testosterone to dihydrotestosterone (DHT) in the prostate.  DHT is the hormone responsible for prostatic growth.

 Finasteride has been shown to reduce the size of the prostate by around 30 per cent, providing an increase in urinary flow rate and improving lower urinary tract symptoms.

Dose regimens

Finasteride 5mg daily. A lower strength (1mg daily) is licensed for the treatment of androgenic alopecia in men.

Dutasteride  500 micrograms daily.

Patient's knowledge of the medicine's use

5-alpha-reductase inhibitors reduce prostate size, improving urinary flow rates and improving symptoms of BPH, they are most effective in patients with large prostates but can be less effective at reducing symptoms than the alpha-adrenoceptor blockers.

Is the medication working?

5-alpha-reductase inhibitors generally take longer to provide symptomatic relief than alpha-adrenoceptor blockers, improving symptoms over a period of several months. So patients should be made aware that it could take a while for the benefits to be seen. However symptomatic relief may continue for several years with continued treatment.

Side effects

Side effects include decreased libido, impotence, reduced ejaculatory volume and reversal of male pattern baldness. Patients should be informed about the potential side effects, especially sexual dysfunction, when discussing the treatment options available.

Monitoring and lifestyle

Patients should be advised to regulate fluid intake to reduce symptoms, particularly before going to bed or going out. Drinks containing alcohol or caffeine should be avoided.

Both drugs are excreted in the semen, so a condom should be recommended if the partner is pregnant. If the sexual partner is of childbearing potential she should be referred to the GP to discuss appropriate methods of contraception.

Women of childbearing potential or already pregnant should not handle broken finasteride tablets or leaking dutasteride capsules.

Any worsening symptoms should be reported to the GP.

Andrew Sturrock is a hospital pharmacist in Gateshead.