5-alpha-reductase inhibitor

5-alpha-reductase inhibitors (5-ARIs), also known as dihydrotestosterone (DHT) blockers, are a class of medications that are primarily used to treat conditions caused by increased levels of dihydrotestosterone, a potent androgen hormone. These conditions include benign prostatic hyperplasia (BPH), prostate cancer, and pattern hair loss in men. In some cases, they are also used to treat hirsutism (excessive hair growth) in women.

Mechanism of Action

5-alpha-reductase inhibitors work by blocking the action of 5-alpha-reductase, the enzyme responsible for the conversion of testosterone into dihydrotestosterone (DHT). By inhibiting this enzyme, 5-ARIs reduce the levels of DHT in the body, leading to a decrease in the size of the prostate in men with BPH, a reduced risk of prostate cancer, and a slowing of hair loss in pattern baldness.

There are two main types of 5-alpha-reductase, type I and type II, with type II being the primary form found in the prostate. Different 5-ARIs have varying affinities for these enzyme types. For example, finasteride selectively inhibits the type II enzyme, while dutasteride inhibits both type I and type II enzymes.

Clinical Uses

Benign Prostatic Hyperplasia

In men with BPH, 5-ARIs can reduce the risk of urinary retention and the need for surgical intervention. These medications are often used in combination with alpha-1 blockers for a synergistic effect on reducing urinary symptoms.

Prostate Cancer

There is evidence to suggest that 5-ARIs may reduce the overall risk of being diagnosed with prostate cancer; however, there is also concern that they may increase the risk of developing high-grade prostate cancer. The use of 5-ARIs for prostate cancer prevention is controversial and should be discussed with a healthcare provider.

Pattern Hair Loss

5-ARIs, particularly finasteride, are effective in treating male pattern hair loss (androgenetic alopecia) by slowing hair loss and promoting hair regrowth in some men.

Hirsutism

In women, 5-ARIs may be used off-label to treat hirsutism by reducing the production of DHT, which can decrease excessive hair growth.

Side Effects

The use of 5-ARIs can be associated with several side effects, including sexual dysfunction (such as decreased libido, erectile dysfunction, and ejaculation disorders), breast tenderness and enlargement, and depression. There is also a risk of high-grade prostate cancer with long-term use. Pregnant women should avoid handling 5-ARIs due to the risk of birth defects in male fetuses.

Available Medications

The most commonly prescribed 5-ARIs are finasteride and dutasteride. These medications are available by prescription and are taken orally.

Conclusion

5-alpha-reductase inhibitors are an important class of medications for managing conditions associated with increased levels of DHT. While they offer significant benefits, their use must be carefully considered against potential risks and side effects. Patients should have a thorough discussion with their healthcare provider to determine if 5-ARIs are appropriate for their condition.