C H A P T E R 5 2
Drugs affecting the urinary tract and the bladder
829
Therapeutic actions and indications
Before any of these drugs are used, it is important to
make sure that the prostate enlargement is benign and
not caused by cancer, infection, stricture or hypotonic
bladder, which would require a different treatment.
Individuals receiving long-term therapy need to be
reassessed periodically to make sure that they have not
developed a serious underlying problem like prostate
cancer. Alpha-adrenergic blockers block postsynaptic
alpha
1
-adrenergic receptors, which results in a dilation
of arterioles and veins and a relaxation of sympathetic
effects on the bladder and urinary tract. In addition to
treating BPH, most of these drugs are also indicated for
treating hypertension (see Chapter 43).
Drugs that block testosterone production—
dutasteride and finasteride—inhibit the intracellular
enzyme that converts testosterone to the potent andro
gen dihydrotestosterone (DHT), which the prostate
gland depends on for its development and maintenance
(see Figure 52.1).
See Table 52.5 for usual indications for alpha-
adrenergic blockers and drugs that block testosterone
production.
Pharmacokinetics
The alpha
1
-selective adrenergic blocking agents are
well absorbed after oral administration, reaching peak
levels in 2 to 8 hours, and undergo extensive hepatic
metabolism. They are excreted in urine. Finasteride and
dutasteride are rapidly absorbed from the GI tract after
oral administration, undergo hepatic metabolism, and
are excreted in faeces and urine.
Contraindications and cautions
Both groups of drugs are contraindicated in individuals
who are allergic to the drugs
to prevent hypersensi-
tivity reactions
. Caution should be used in individuals
with hepatic or renal dysfunction,
which could alter the
metabolism and excretion of the drugs.
The adrenergic
blockers should be used with caution in individuals with
heart failure or known coronary disease,
which could
be aggravated by the drop in blood pressure or tachy-
cardia
. Finasteride and dutasteride have no indications
for women and are rated pregnancy category X
because
of androgen effects
. Women must be cautioned not to
touch finasteride or dutasteride tablets
because of the
risk of absorption through the skin.
Adverse effects
Adverse effects of alpha-adrenergic blockers include
headache, fatigue, dizziness, postural dizziness,
lethargy, tachycardia, hypotension, GI upset and sexual
dysfunction, all of which are effects seen with blockade
of the alpha-receptors. Tamsulosin is not associated
with as many adverse adrenergic-blocking effects as
the other agents. Finasteride and dutasteride are asso-
ciated with decreased libido, impotence and sexual
dysfunction, all of which are related to decreased levels
of DHT. People using either finasteride or dutasteride
cannot donate blood for 6 months after the last dose to
protect potential blood recipients from exposure to the
testosterone-blocking effects.
Clinically important drug–drug interactions
There is a possibility of increased antihypertensive
effects if the alpha-adrenergic blockers are combined
TABLE 52.5
DRUGS IN FOCUS Drugs for treating benign prostatic hyperplasia (BPH)
Drug name
Dosage/route
Usual indications
Alpha-adrenergic blockers
alfuzosin (Xatral SR)
10 mg/day PO, take after the same meal each
day
Relief of symptoms of BPH
tamsulosin (Flomaxtra)
0.4–0.8 mg/day PO, 30 minutes after the same
meal each day
Treatment of BPH
terazosin (Hytrin)
1–20 mg/day PO based on the person’s
response
Relief of symptoms of BPH; hypertension
Drugs that block testosterone production
dutasteride (Avodart)
0.5 mg/day PO
Long-term treatment of symptomatic
BPH to shrink the prostate and relieve
symptoms of hyperplasia
finasteride (Proscar,
Propecia)
5 mg/day PO for BPH, 1 mg/day PO for male-
pattern baldness (Propecia)
Long-term treatment of symptomatic
BPH to shrink the prostate and relieve
symptoms of hyperplasia; prevention of
male-pattern baldness in people with
strong family history
