McKenna's Pharmacology for Nursing, 2e

C H A P T E R 5 2 Drugs affecting the urinary tract and the bladder 821

TABLE 52.2

DRUGS IN FOCUS Urinary tract anti-infectives

Drug name

Dosage/route

Usual indications

hexamine hippurate (Hiprex)

1 g b.d. PO Paediatric (6–12 years): 0.5–1 g PO b.d.

Suppression or elimination of bacteriuria associated with UTIs and anatomical abnormalities Treatment of UTIs caused by susceptible bacteria

nitrofurantoin

50–100 mg PO q.i.d. for 10–14 days; 50–100 mg PO at bedtime for chronic suppressive therapy Paediatric: 5–7 mg/kg per day in four divided doses 400 mg q 12 hours PO, length of therapy dependent on site and intensity of infection

(Macrodantin)

Treatment of UTIs caused by susceptible bacteria (broad-spectrum agent); treatment of uncomplicated urethral and cervical gonorrhoea and prostatitis

norfloxacin (Noroxin, Roxin)

not specific to urinary tract infections and are also used for treating other infections (see Chapter 9). The other type of urinary tract anti-infective works to acidify the urine, killing bacteria that might be in the bladder. This group includes hexamine hippurate ( Hiprex ). Therapeutic actions and indications Urinary tract anti-infectives act specifically within the urinary tract to destroy bacteria, either through a direct antibiotic effect or through acidification of the urine. They do not generally have an antibiotic effect system- ically, being activated or effective only in the urinary tract (Figure 52.1). Those drugs with an antibiotic effect interfere with reproduction of the gram-negative bacteria and cause bacterial cell death. Those that cause acidification of the urine produce an environment that is not conducive to bacterial survival, leading to bacterial

cell death. They are used to treat chronic UTIs, as adjunctive therapy in acute cystitis and pyelonephritis, and as prophylaxis with urinary tract anatomical abnor- malities and residual urine disorders. See the Critical thinking scenario for additional information regarding teaching the person about treatment with hexamine hippurate for cystitis . Table 52.2 discusses usual indications for each of the urinary tract anti-infectives. Pharmacokinetics Norfloxacin, a newer and broader-spectrum drug, is effective against even more gram-negative strains. This drug is rapidly absorbed when taken orally and under- goes hepatic metabolism and renal excretion. The dose of norfloxacin must also be reduced in the presence of renal impairment. Nitrofurantoin is another older drug with a very short half-life (20 to 60 minutes). It is not effective against as many gram-negative bacteria as the newer drugs are, but it has been successfully used for suppres- sion therapy in adults and children with chronic UTIs. It is well absorbed when taken orally, metabolised in the liver and excreted in urine. No dose adjustment is needed with renal impairment. Hexamine hippurate, taken orally, is well absorbed, undergoes metabolism in the liver and is excreted in urine. Norfloxacin, nitrofurantoin and hexamine hippu- rate cross the placenta and enter breast milk. Contraindications and cautions These drugs are contraindicated in the presence of any known allergy to any of these drugs to prevent hyper- sensitivity reactions . They should be used with caution in the presence of renal dysfunction, which could inter- fere with the excretion and action of these drugs, and with pregnancy and breastfeeding because of the poten- tial for adverse effects on the fetus or neonate.

Urinary tract antispasmodics work here

Urinary tract analgesics work here

Muscle layer

Urinary bladder Ureter Fundus of bladder Epithelial layer Opening of ureter Muscle layer Neck of bladder Urethral sphincter

Urinary tract anti-infectives work here

Endothelial layer

Bladder protectants work here

Prostate gland Urethra

Drugs used to treat BPH work here

FIGURE 52.1  Sites of action of drugs acting on the urinary tract.