McKenna's Pharmacology for Nursing, 2e

C H A P T E R 5 2 Drugs affecting the urinary tract and the bladder 825

TABLE 52.3

DRUGS IN FOCUS Urinary tract antispasmodics

Drug name

Dosage/route

Usual indications

darifenacin (Enablex)

7.5 mg/day PO; may be increased to 15 mg/day

Treatment of overactive bladder in people with urinary urgency, incontinence or frequency Symptomatic relief of urinary bladder spasm; treatment of overactive bladder

5 mg PO t.d.s. to q.i.d.; ER tablets—5 mg/day PO up to a maximum 30 mg/day Transdermal patch: apply to dry, intact skin q 3–4 days Paediatric (>5 yr): 5 mg PO b.d., up to a maximum 5 mg PO t.d.s.

oxybutynin (Ditropan, Oxytrol)

solifenacin (Vesicare)

5–10 mg/day PO

Treatment of overactive bladder in people with urinary urgency, incontinence or frequency Treatment of overactive bladder in people with urinary urgency, frequency or incontinence

tolterodine (Detrusitol)

1–2 mg PO b.d.; ER capsules—4 mg/day; reduce dose in people with hepatic impairment to 1 mg PO b.d.

Contraindications and cautions These drugs are contraindicated in the presence of known allergy to the drugs to avoid hypersensitiv- ity reactions ; with pyloric or duodenal obstruction or recent surgery because the anticholinergic effects can cause serious complications ; with obstructive urinary tract problems, which could be further aggravated by the blocking of muscle activity ; and with glaucoma, myasthenia gravis or acute haemorrhage, which could all be exacerbated by the anticholinergic effects of these drugs. Caution should be used in people with renal or hepatic dysfunction, which could alter the metabolism and excretion of the drugs , and in pregnant and breast- feeding women because of potential adverse effects on the fetus or neonate secondary to the anticholinergic effects of the drugs. Adverse effects Adverse effects of urinary tract antispasmodics are related to the blocking of the parasympathetic system and include nausea, vomiting, dry mouth, nervousness, tachycardia and vision changes. Oxybutynin has numerous anticholinergic effects, making it undesirable in certain conditions or situations that might be aggravated by decreased sweating, urinary retention, tachycardia and changes in GI activity. Clinically important drug–drug interactions Decreased effectiveness of phenothiazines and haloper- idol has been associated with the combination of these drugs with oxybutynin. If any such combinations must be used, the person should be monitored closely and appropriate dose adjustments made. There is a risk of

increased QT interval and serious cardiac arrhythmias if solifenacin is combined with other drugs that prolong the QT interval (antihistamines, antipsychotics); the person must be monitored closely if this combination is used. There is also a risk of increased serum levels and toxic effects if solifenacin is combined with ketocona- zole or other cytochrome P450 (CYP) 3A4 inhibitors; the dose of solifenacin must be reduced and the person monitored closely. Tolterodine levels and toxicity can increase if it is taken with CYP 2D6 inhibitors (fluox- etine); the dose of tolterodine must be reduced if this combination is used. Prototype summary: Oxybutynin Indications: Relief of symptoms of bladder instability associated with uninhibited neurogenic and reflex neurogenic bladder; treatment of signs and symptoms of overactive bladder. Actions: Acts directly to relax smooth muscle in the bladder; inhibits the effects of acetylcholine at muscarinic receptors. Pharmacokinetics: Route Onset Peak Duration Oral 30–60 mins 3–6 hours 6–10 hours Transdermal system Varies 6–8 hours 96 hours T 1/2 : Unknown; metabolised in the liver and excreted in urine. Adverse effects: Drowsiness, dizziness, blurred vision, tachycardia, dry mouth, nausea, urinary hesitancy, decreased sweating.