Which statement accurately describes DHT suppression by dutasteride compared with finasteride and its potential clinical implication?

• A. Finasteride inhibits both type I and II and provides broader suppression; dutasteride is less effective.
• B. Dutasteride inhibits only type I; hence less suppression.
• C. Dutasteride inhibits both type I and II 5-alpha-reductase, providing broader DHT suppression and potentially greater efficacy in some patients.
• D. Both drugs have identical isoenzyme inhibition and potency.

Answer: (C)

The concept here is how inhibition of 5-alpha-reductase isoenzymes affects DHT levels and treatment outcomes. There are two isoforms of 5-alpha-reductase in the body, type I and type II. Finasteride mainly inhibits the type II isoenzyme, with limited inhibition of type I. Dutasteride, on the other hand, inhibits both type I and type II, leading to a more complete suppression of DHT across tissues where these enzymes are active.

Because dutasteride blocks both isoenzymes, it can reduce DHT levels more profoundly than finasteride. This broader suppression can translate into greater efficacy in conditions driven by DHT—such as androgenetic alopecia and benign prostatic hyperplasia—in some patients, though individual response and side effects also play important roles.

The other statements don’t fit because finasteride is not broad-spectrum for both isoenzymes, dutasteride is not limited to type I, and the two drugs do not have identical isoenzyme inhibition or potency.