McKenna's Pharmacology for Nursing, 2e

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P A R T 5  Drugs acting on the autonomic nervous system

Drug therapy across the lifespan

BOX 33.1

( Atrovent ), propantheline ( Pro-Banthine ), and tiotro- pium ( Spiriva ) (see Table 33.1). Therapeutic actions and indications The anticholinergic drugs competitively block the acetyl- choline receptors at the muscarinic cholinergic receptor sites that are responsible for mediating the effects of the parasympathetic postganglionic impulses (Figure 33.1). Some are more specific to particular receptors in the res- piratory, genitourinary (GU) or GI tracts, making them preferred for treating specific conditions, and others more generally depress the parasympathetic system. When the parasympathetic system is blocked, the effects of the sympathetic system are more prominently seen. These drugs can be used to decrease secretions before anaesthesia; to treat parkinsonism (by blocking the stimulating effects of acetylcholine); to restore cardiac rate and blood pressure after vagal stimulation during surgery; to relieve bradycardia caused by a hyperactive carotid sinus reflex; to relieve pylorospasm and hyper- active bowel; to relax biliary and ureteral colic; to relax bladder detrusor muscles and tighten sphincters; to help to control crying or laughing episodes in people with brain injuries; to relax uterine hypertonicity; to help in the management of peptic ulcer; to control rhinorrhoea associated with hay fever; as an antidote for choliner- gic drugs and for poisoning by certain mushrooms; and as an ophthalmic agent to cause mydriasis or cyclo- plegia in acute inflammatory conditions (Table 33.1). Anticholinergic agents/parasympatholytics CHILDREN The anticholinergic agents are often used in children. Children are often more sensitive to the adverse effects of the drugs, including constipation, urinary retention, heat intolerance and confusion. If a child is given one of these drugs, the child should be closely watched and monitored for adverse effects, and appropriate supportive measures should be instituted. ADULTS Adults need to be made aware of the potential for adverse effects associated with the use of these drugs.They should be encouraged to void before taking the medication if urinary retention or hesitancy is a problem.They should be encouraged to drink plenty of fluids and to avoid hot temperatures because heat intolerance can occur and it will be important to maintain hydration should this happen. Safety precautions may be needed if blurred vision and dizziness occur.The person should be urged not to drive or perform tasks that require concentration and coordination. PREGNANCY AND BREASTFEEDING These drugs should not be used during pregnancy because they cross the placenta and could cause adverse

Anticholinergic drugs also are thought to block the effects of acetylcholine in the central nervous system (CNS), which may account for their effectiveness in treating motion sickness. Atropine, the prototype drug, has been used for many years and is derived from the plant belladonna . (Belladonna was once used by fashionable ladies of the European courts to dilate their pupils in an effort to make them more innocent looking and alluring.) Atropine is used to depress salivation and bronchial secretions and to dilate the bronchi, but it can thicken respiratory secre- tions (causing obstruction of airways). Atropine is also used to inhibit vagal responses in the heart, to relax the GI and GU tracts, to inhibit GI secretions, to cause mydriasis or relaxation of the pupil of the eye (also called a mydriatic effect) and to cause cycloplegia , or inhibition of the ability of the lens in the eye to accommodate to near vision (also called a cycloplegic effect). Atropine works by blocking only the muscarinic effectors in the parasympathetic nervous system and the few cholinergic receptors in the sympathetic nervous system (SNS), such as those that control sweating. It acts by competing with acetylcholine for the muscarinic ace- tylcholine receptor sites. It does not block the nicotinic receptors and therefore has little or no effect at the neu- romuscular junction. Ipratropium and tiotropium act more specifically to decrease respiratory secretions and cause bronchodila- tion. They are used as bronchodilators and to decrease symptoms of upper respiratory irritation. These agents OLDER ADULTS Older adults are more likely to experience the adverse effects associated with these drugs; dose should be reduced, and the person should be monitored very closely. Because older people are more susceptible to heat intolerance owing to decreased body fluid and decreased sweating, extreme caution should be used when an anticholinergic drug is given.The person should be urged to drink plenty of fluids and to avoid extremes of temperature or exertion in warm temperatures.The older adult is more likely to experience confusion, hallucinations and psychotic syndromes when taking an anticholinergic drug. Safety precautions may be needed if central nervous system effects are severe. Older adults may also have renal impairment, making them more likely to have problems excreting these drugs. Further reduction in dose may be needed in the older person who also has renal dysfunction. effects on the fetus. If the benefit to the mother clearly outweighs the potential risk to the fetus, they should be used with caution. Breastfeeding women should find another method of feeding the baby if an anticholinergic drug is needed because of the potential for serious adverse effects on the baby.