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Dutasteride (marketed as Avodart, Avidart, Avolve, Duagen, Dutas, Dutagen, Duprost) is a 5-alpha-reductase inhibitor, a drug which inhibits the conversion of testosterone into dihydrotestosterone (DHT). It is used to treat conditions caused by DHT, such as benign prostatic hyperplasia (BPH).

Classification and Method of Action

Dutasteride belongs to a class of drugs called 5-alpha-reductase inhibitors, which block the action of the 5-alpha-reductase enzymes that convert testosterone into dihydrotestosterone (DHT). Finasteride also belongs to this group. Dutasteride inhibits both isoforms of 5-alpha reductase, while finasteride inhibits only one. But a clinical study done by GlaxoSmithKline, the EPICS trial, did not find dutasteride to be more effective than finasteride in treating BPH.


Dutasteride is used to treat an enlarged prostate (benign prostatic hyperplasia, or BPH). Dutasteride shrinks the prostate, relieves symptoms of BPH, such as frequent and difficult urination, and decreases the chance that surgery will be needed to treat this condition.

While dutasteride is officially approved to treat enlargement of the prostate gland, it may also be used to treat male pattern baldness. But clinical trials for dutasteride as a hair loss drug were called off in late 2002. The reason the trials were called off is not publicly known. Industry sources speculate that Avodart would have been seen as too similar to Propecia to have proved profitable as a hair loss treatment.

In December 2006, Avodart manufacturer GlaxoSmithKline embarked on a new Phase III, six month study in Korea to test the safety, tolerability and effectiveness of a once-daily dose of dutasteride (0.5mg) for the treatment of male pattern baldness in the vertex region of the scalp (types IIIv, IV and V on the Hamilton-Norwood scale).[1] The future impact that this study will have on the FDA's approval or disapproval of Avodart for the treatment of male pattern baldness in the United States is yet to be determined.

Dutasteride is sometimes prescribed as a supplemental anti-androgen in male to female hormone therapy. While it has not been studied and it's beneficial effects have not been documented it is thought that the drug will inhibit the formation of the more powerful dihydrotestosterone (DHT) from whatever testosterone is left in the body after the main anti-androgen has done its work.

Side Effects

Dutasteride may cause side effects. The prescribing physician should be told if any of these symptoms are severe or do not go away:

  • inability to have or maintain an erection
  • decrease in sex drive
  • difficulty ejaculating
  • breast tenderness or enlargement

Dutasteride may cause other side effects. The prescribing physician should be notified if any unusual problems occur while taking this medication.

Precautions on Taking Dutasteride

The prescribing doctor and pharmacist should be told what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products are being taken. Be sure that any of the following are mentioned:

  • Antifungals such as fluconazole, (Diflucan), itraconazole (Sporanox), and ketoconazole (Nizoral); cimetidine (Tagamet); ciprofloxacin (Cipro); clarithromycin (Biaxin); cyclosporine (Neoral, Sandimmune); danazol (Danocrine); delavirdine (Rescriptor); diltiazem (Cardizem, Dilacor, Tiazac); erythromycin (E.E.S., E-Mycin, Erythrocin); fluoxetine (Prozac, Sarafem); fluvoxamine (Luvox);
  • HIV protease inhibitors such as indinavir (Crixivan) and ritonavir (Norvir); isoniazid (INH, Nydrazid); metronidazole (Flagyl); nefazodone (Serzone); troleandomycin (TAO); verapamil (Calan, Covera, Isoptin, Verelan); and zafirlukast (Accolate).

The prescribing physician may need to change the dosage of these medications or monitor more carefully for side effects. The doctor must also be informed if the patient has or have ever had liver disease or prostate cancer.

Dutasteride is for use only in men. Women, especially those who are or may become pregnant, should not handle dutasteride capsules. Touching the contents of the capsules may harm the fetus. Women who accidentally touch leaking capsules should wash the area with soap and water immediately.

Blood donation is prohibited while taking dutasteride and for 6 months after the use of the medication is discontinued.

Drinking grapefruit juice should be avoided while taking this medicine. Grapefruit, more specifically a compound in grapefruit that has yet to be identified, inhibits the activity of of an enzyme that helps break down or metabolize the drug. If a drug is not adequately metabolized, higher levels of the drug than intended may enter the bloodstream, which can lead to a potentially dangerous situation.

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