McKenna's Pharmacology for Nursing, 2e

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. -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. Pharmacokinetics The alpha 1

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 0.4–0.8 mg/day PO, 30 minutes after the same meal each day 1–20 mg/day PO based on the person’s response

Relief of symptoms of BPH

tamsulosin (Flomaxtra)

Treatment of BPH

terazosin (Hytrin)

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 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

finasteride (Proscar, Propecia)

5 mg/day PO for BPH, 1 mg/day PO for male- pattern baldness (Propecia)