Case 1: The alpha-1 antagonists, including tamsulosin (Flomax), alfuzosin (Uroxatral), doxazosin (Cardura), silodosin (Rapaflo), and terazosin (Hytrin), are approved for the symptomatic treatment of BPH. Alpha-1 antagonists lead to relaxation of smooth muscle found in the prostatic urethra, bladder neck, and prostate capsule, leading to relief of lower urinary tract symptoms (LUTS). These agents do not affect the size of the prostate. Finasteride (Proscar) and dutasteride (Avodart) are 5-alpha reductase inhibitors that also have FDA approval for the treatment of symptoms due to BPH. These agents work by inhibiting the conversion of testosterone to dihydrotestosterone within androgensensitive tissue such as the prostate, leading to a reduction in prostate size and improvement in LUTS. Therefore, if a patient diagnosed with BPH also presents with evidence of prostate enlargement, such as an elevated prostate-specific antigen level, guidelines suggest selection of a 5-alpha reductase inhibitor over an alpha-1 antagonist. If there is no evidence of prostate enlargement, initiating therapy with an alpha-1 antagonist is appropriate. Treatment initiation is also dependent on the severity of LUTS and the degree to which they interfere with activities of daily living (ADLs), as watchful waiting is an option if the LUTS are mild or moderate to severe but do not interfere with ADLs.
Case 2: Dutasteride is used to treat symptomatic BPH due to an enlarged prostate. It works by competitive inhibition of 5-alpha reductase, blocking the conversion of testosterone to dihydrotestosterone (DHT). DHT is a hormone necessary for normal development of male genitalia. Evidence of this has been shown in animal studies where dutasteride inhibited the development of male fetus external genitalia, making it a pregnancy category X. Therefore, pregnant women, or women who may become pregnant, should not handle dutasteride because of development risks to the fetus. Due to dutasteride’s long half-life, serum concentrations of the drug may remain detectable for up to 4 to 6 months after discontinuation of therapy. For this reason, men wanting to donate blood should wait a minimum of 6 months after cessation of dutasteride therapy to avoid exposure to female blood recipients who may be pregnant.