5-alpha-reductase Inhibitors
The 5-alpha-reductase inhibitors include the drugs finasteride (Proscar) and dutasteride (Avodart). They block the action of 5-alpha-reductase, an enzyme that normally converts the male hormone testosterone to another type of male hormone, dihydrotestosterone. Dihydrotestosterone stimulates the prostate cell division and is important in prostate growth. As the drugs prevent 5-alpha-reductase from producing dihydrotestosterone, the prostate no longer grows larger and actually begins to shrink.
Finasteride has been shown to improve urine flow and prevent urinary retention (having urine in the bladder after trying to empty it) after about 3 to 6 months. However, it may take as long as a year to see the full benefit of finasteride in improving urinary symptoms. Finasteride also stops or slows down the progression of BPH.
There is more than one type of 5-alpha-reductase enzyme. Finasteride works by blocking 5-alpha-reductase Type 2. The drug reduces the levels of dihydrotestosterone by as much as 70 percent in the blood, and by as much as 90 percent in the prostate. Over time, in men who continue to take it every day, finasteride may reduce the volume of the prostate gland by about 20 percent.
Studies suggest that finasteride works best in men with larger prostates. It should not be given to men without prostate enlargement. The drug does not affect testosterone levels or the ability of testosterone to stimulate normal male functions. A few men may experience sexual problems (lack of desire, problems with erections or ejaculation) or breast enlargement or tenderness after taking finasteride. However, these side effects are uncommon.
Dutasteride blocks the action of both 5-alpha-reductase Type 1 and Type 2. This reduces the blood levels of dihydrotestosterone by more than 90 percent in most men. Like finasteride, dutasteride reduces the volume of the prostate, improves urinary symptoms and stops or slows down the progression of BPH. Dutasteride may work faster than finasteride, though it still takes months to see its full benefits.
Like finasteride, dutasteride works best in men with larger prostates. It should not be prescribed to men with LUTS who do not have prostate enlargement. Side effects with dutasteride are uncommon, affecting a small percentage of men who take it. When side effects occur, they involve the same kinds of sexual problems or breast enlargement or tenderness that have been reported for finasteride.