Figure 25.24 • Steroid 5a-reductase inhibitors.
bis(trifluoromethyl)phenyl}-3-oxo-4-azaandrost-1-ene-17-carboxamide (Avodart) a newer drug for treating BPH, inhibits both isoforms of the enzyme (Fig. 25.24). Dutasteride bears an aromatic amide at C17, rather than the t-butyl amide seen in finasteride. Both drugs are effective at treating BPH, but a recent retrospective study suggests that rates of acute urinary retention are lower with dutasteride.134 It is not yet known, however, if this reduced urinary retention is a result of the dual inhibition nature of dutasteride. Dutasteride inhibits 5a--reductase by the same mechanism as finasteride and has a long terminal elimination half-life, which is approximately 5 weeks at steady state. In addition to the treatment of BPH, dutasteride is being investigated for its ability to delay the progression of
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