Finasteride (Propecia, Proscar - Merck), a synthetic lipophilic analog of the male hormone testosterone, is a dihydrotestosterone (DHT) inhibitor and effective anti-androgen. Finasteride is indicated for male pattern baldness (MPB) and benign prostate hyperplasia (BPH). As a 5-alpha-reductase (5-AR) inhibitor, finasteride reduces DHT levels by preventing the enzymatic conversion or metabolism of testosterone through the 5-AR enzyme. Therapeutic efficacy of finasteride is correlated with 65-70% serum (circulating) reduction of DHT, and localized reduction in the prostate of up to 85-90%.
5-AR reduces the 4,5 double bond of the male hormone testosterone, converting it into the biologically-active DHT hormone. At the receptor, DHT is three times more potent than testosterone; DHT conversion from testosterone takes place primarily in the hair follicles, prostate, testicles, and adrenal glands. DHT is non-aromatizing, meaning it is not converted to estradiol or other estrogenic metabolic products via aromatase.
DHT is the primary factor implemented in common male pattern baldness and a minority subset of female baldness cases. DHT plays a role in the development and progression of benign prostatic hyperplasia (BPH), as well as in prostate cancer, via enlargement of the prostate gland. Healthy physiological processes, including normal growth of prostate cells and prostate cell differentiation, also depend heavily on DHT.
Of the three 5-alpha reductase isozymes (type I, type II, and type III), finasteride is a partial inhibitor of types II and III. Because of the lack of activity towards the type I 5-AR isozyme, finasteride does not fully inhibit the production of DHT. Dutasteride (Avodart, GlaxoSmithKline), a “triple inhibitor,” reduces DHT levels up to 99% and carries a higher documented risk of erectile dysfunction, reduced libido, and other sexual side-effects in men.
Finasteride is applied in treatment for benign prostatic hypetrophy at a dose of 5 mg taken once daily. Treatment is usually effective within six months, with reversal of therapeutic benefits typical if treatment is ceased. Finasteride also treats symptoms associated with BPH: difficulty urinating ("prostate pinch"), sleep disturbance at night due to excessive frequency of urination, difficulty initiating urination, and decreased urinary flow.
Lower dosages of approximately 20% (1mg) are indicated for male pattern baldness. 48% of those treated with Propecia (1 mg of finasteride) had some regrowth of hair, and a further 42% had no further loss. Hair count in the treatment group remained above baseline on average, with increasing difference from hair count in the placebo group, for the duration of the study. Finasteride is effective only for as long as it is taken; the hair gained or maintained is lost within 6–12 months of ceasing therapy. Finasteride, like minoxidil (Rogaine), was shown to work on both the crown area and the hairline with significantly more success in reversing hair-loss in the crown region.
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