5a-reductase, inhibitors

Anti-androgens and hormones 5a-Reductase inhibitors Progesterone and estrogen Recreational drugs Ethanol Cocaine Marijuana... 

Compare and contrast a-adrenergic antagonists versus 5a-reductase inhibitors in terms of mechanism of action, treatment outcomes, adverse effects, and interactions when used for management of benign prostatic hyperplasia. 

The testes and adrenal glands produce 90% and 10%, respectively, of circulating testosterone. Testosterone enters prostate cells, where predominantly type II 5a-reductase activates testosterone to dihydrotestosterone, which combines with a cytoplasmic receptor. The complex enters the nucleus and induces changes in protein synthesis which promote glandular tissue growth of the prostate. Thus, 5a-reductase inhibitors (e.g., finasteride and dutas-teride) directly interfere with one of the major etiologic factors of BPH. 

In an enlarged gland, the epithelial/stromal tissue ratio is 1 5.3 Androgens stimulate epithelial, but not stromal tissue hyperplasia. Hence, androgen antagonism does not induce a complete reduction in prostate size to normal. This explains one of the limitations of the clinical effect of 5a-reductase inhibitors. 

For patients with moderate to severe symptoms, the patient is usually offered drug treatment first. a-Adrenergic antagonists are preferred over 5a-reductase inhibitors because the former have a faster onset of action (days to a few weeks) and improve symptoms independent of prostate size. 5a-reductase inhibitors have a delayed onset of action (i.e., peak effect may... 

TABLE 49-4. Comparison of a-Adrenergic Antagonists and 5a-Reductase Inhibitors for Treatment of Benign Prostatic Hyperplasia47... 

Drug treatment failures may result from a variety of factors. Initial failure to respond to a-adrenergic antagonists occurs in 20% to 70% of treated patients. It is likely in these patients that the static factor may predominate as the cause of symptoms in these patients. Initial failure to respond to 5a-reductase inhibitors occurs in 30% to 70% of treated patients. 

If the patient is started on a 5a-reductase inhibitor, monitor the patient for drug-induced decreased libido, erectile dysfunction, or ejaculation disorders. If severe, discontinue the drug. 

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