McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 3 3 Anticholinergic agents

pregnancy because of the potential for adverse effects to the fetus ; hypertension because of the possibility of additive hypertensive effects from the sympathetic system’s dominance with parasympathetic nervous system blocking ; and spasticity and brain damage, which could be exacerbated by cholinergic blockade within the CNS. Adverse effects The adverse effects associated with the use of antichol­ inergic drugs are caused by the systemic blockade of cholinergic receptors. What are adverse effects in some cases may be the desired therapeutic effects in others (Table 33.2). The intensity of adverse effects is related to drug dose: the more of the drug in the system, the greater are the systemic effects. These adverse effects could include CNS effects, such as blurred vision, pupil dilation and resultant photophobia, cycloplegia and increased intraocular pressure, all of which are related to the blocking of the parasympathetic effects in the eye. Weakness, dizziness, insomnia, mental confusion and excitement are effects related to cholinergic receptor

blockade within the CNS. Dry mouth results from the blocking of GI secretions. Altered taste perception, nausea, heartburn, constipation, bloated feelings and paralytic ileus are related to a slowing of GI activity. Tachycardia and palpitations are possible effects related to blocking of the parasympathetic effects on the heart. Urinary hesitancy and retention are related to the blocking of bladder muscle activity and sphincter relaxa- tion. Decreased sweating and an increased predisposition to heat prostration are related to the inability to cool the body by sweating, a result of blocking of the sympathetic cholinergic receptors responsible for sweating. Suppres- sion of breastfeeding is related to anticholinergic effects in the breasts and in the CNS. The severity of the adverse effects is related to the dose of the drug. Clinically important drug–drug interactions The incidence of anticholinergic effects increases if these drugs are combined with any other drugs with anticholinergic activity, including antihistamines, antiparkinsonism drugs, monoamine oxidase (MAO) inhibitors and tricyclic antidepressants (TCAs). If

■■ TABLE 33.2 Effects of parasympathetic blockade and associated therapeutic uses Physiological effect Therapeutic uses

Gastrointestinal Smooth muscle: blocks spasm, blocks peristalsis Secretory glands: decreases acid and digestive enzyme production Urinary tract Decreases tone and motility in the ureters and fundus of the bladder; increases tone in the bladder sphincter

Decreases motility and secretory activity in peptic ulcer, gastritis, cardiospasm, pylorospasm, enteritis, diarrhoea, hypertonic constipation Increases bladder capacity in children with enuresis, spastic paraplegics; decreases urinary urgency and frequency in cystitis; antispasmodic in renal colic and to counteract bladder spasm caused by morphine

Biliary tract Relaxes smooth muscle, antispasmodic

Relief of biliary colic; counteracts spasms caused by narcotics

Bronchial muscle Weakly relaxes smooth muscle

Aerosol form may be used in asthma; may counteract bronchoconstriction caused by drugs

Cardiovascular system Increases heart rate (may decrease heart rate at very low doses); causes local vasodilation and flushing

Counteracts bradycardia caused by vagal stimulation, carotid sinus syndrome, surgical procedures; used to overcome heart blocks following MI; used to counteract hypotension caused by cholinergic drugs Allows ophthalmological examination of the retina, optic disc; relaxes ocular muscles and decreases irritation in iridocyclitis, choroiditis Preoperatively before inhalation anaesthesia; reduces nasal secretions in rhinitis, hay fever; may be used to reduce excessive sweating in hyperhidrosis

Ocular effects Pupil dilation, cycloplegia

Secretions Reduces sweating, salivation, respiratory tract secretions

Central nervous system Decreases extrapyramidal motor activity Atropine may cause excessive stimulation, psychosis, delirium, disorientation

Decreases tremor in parkinsonism; helps to prevent motion sickness