Prostate disease and the pharmaceutical industry

5-alpha reductase inhibitors

Biochemical studies have shown that the male hormone testosterone is converted in the prostate to a related compound called dihydrotestosterone (DHT). DHT helps regulate prostate growth and it seemed plausible that medicines to block DHT formation might prevent prostate enlargement.

Testosterone is converted to DHT by a special enzyme called 5-alpha reductase. This exists in two forms, called Type 1 and Type 2. The major one found in the prostate is Type 2 and after a lengthy research programme, scientists at Merck Sharp & Dohme developed an inhibitor of this enzyme called finasteride. Studies showed that it not only reduced enlargement, but also could shrink an already enlarged prostate. In the two-thirds of men who respond, the reduction in prostate volume ranges from 20 to about 40 per cent, depending on the length of treatment and often leads to an early improvement in symptoms. However, finasteride may take up to six months’ treatment to assess whether a beneficial response has been achieved. In men who do respond (usually those with very large prostates – 40-50 grammes in weight), there may be a gradual further improvement lasting for several years and treatment should continue long-term. Generally, finasteride is well tolerated, but about one man in 20 may experience some loss of interest in sex and difficulty in achieving erections. As with the alpha-blockers, some men will eventually need other forms of treatment, though finasteride reduced the risk of requiring surgery by 55 per cent compared with placebo.

One other medicine in this category is a lipido-sterolic extract of the dwarf palm tree (Pierre Fabre). This is available in much of Europe, but not the UK. It is interesting in that it blocks both Type 1 and Type 2 forms of 5-alpha reductase, also shows anti-inflammatory activity and can stop cells dividing, all actions that may contribute to its effectiveness in people with BPH.