McKenna's Pharmacology for Nursing, 2e

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P A R T 4  Drugs acting on the central and peripheral nervous systems

Adverse effects The use of anticholinergics for Parkinson’s disease and parkinsonism is associated with CNS effects that relate to the blocking of central acetylcholine receptors, such as disorientation, confusion and memory loss. Agita- tion, nervousness, delirium, dizziness, light-headedness and weakness may also occur. Anticipated peripheral anticholinergic effects include dry mouth, nausea, vomiting, paralytic ileus and consti- pation related to decreased GI secretions and motility. In addition, other adverse effects may occur, includ- ing tachycardia, palpitations and hypotension related to the blocking of the suppressive cardiac effects of the parasympathetic nervous system; urinary retention and hesitancy related to a blocking of bladder muscle activity and sphincter relaxation; blurred vision and photophobia related to pupil dilation and blocking of lens accommodation; and flushing and reduced sweating related to a blocking of the cholinergic sites that stimu- late sweating and blood vessel dilation in the skin. Clinically important drug–drug interactions When these anticholinergic drugs are used with other drugs that have anticholinergic properties, including the tricyclics antidepressants and the phenothiazines, there is a risk of potentially fatal paralytic ileus and an increased risk of toxic psychoses. If such combinations must be given, monitor people closely and implement supportive measures. Dose adjustments are often neces- sary. In addition, when antipsychotic drugs are combined Prototype summary: Biperiden Indications: Adjunctive therapy for Parkinson’s disease; relief of symptoms of extrapyramidal disorders (parkinsonism). Actions: Acts as an anticholinergic, principally in the CNS, returning balance to the basal ganglia and reducing the severity of rigidity, akinesia and tremors; peripheral anticholinergic effects help to reduce drooling and other secondary effects of parkinsonism. Pharmacokinetics: Route Onset Peak Duration Oral 1 hours 1–1.5 hours 6–12 hours IM 15 mins Unknown Unknown T 1/2 : 18.4 to 24.3 hours; metabolised in the liver. Adverse effects: Disorientation, confusion, memory loss, nervousness, light-headedness, dizziness, depression, blurred vision, mydriasis, dry mouth, constipation, urinary retention, urinary hesitation, flushing, decreased sweating.

affinity for cholinergic receptor sites in the CNS than for those in the peripheral nervous system. However, they still block, to some extent, the cholinergic receptors that are responsible for stimulation of the parasympathetic nervous system’s postganglionic effectors. This blockage is associated with the adverse effects (see Chapter 33), including slowed gastrointestinal (GI) motility and secretions, with dry mouth and constipation, urinary retention, blurred vision and dilated pupils. Anticholinergic drugs are indicated for the treatment of parkinsonism, whether idiopathic, atherosclerotic or postencephalitic, and for the relief of symptoms of extrapyramidal disorders associated with the use of some drugs, including phenothiazines. Although these drugs are not as effective as levodopa in the treatment of advancing cases of the disease, they may be useful as adjunctive therapy and for people who no longer respond to levodopa. See Table 24.2 for usual indications. Pharmacokinetics The anticholinergic drugs are variably absorbed from the GI tract, reaching peak levels in 1 to 4 hours. They are metabolised in the liver and excreted by cellular pathways. All of them cross the placenta and enter breast milk (see Contraindications and cautions). Benztropine and biperiden are available in oral and intramuscular/ intravenous forms. Benzhexol is only available in an oral form. Contraindications and cautions Anticholinergics are contraindicated in the presence of allergy to any of these agents to avoid hypersensitivity reactions . Inaddition, they are contraindicated innarrow- angle glaucoma, GI obstruction, genitourinary (GU) obstruction and prostatic hypertrophy, all of which could be exacerbated by the peripheral anticholin- ergic effects of these drugs , and in myasthenia gravis, which could be exacerbated by the blocking of acetyl- choline-receptor sites at neuromuscular synapses. The safety and efficacy for use in children have not been established. Administer these agents cautiously in the following conditions: tachycardia and other dysrhythmias and hypertension or hypotension because the blocking of the parasympathetic system may cause a dominance of sympathetic stimulatory activity , and hepatic dys- function, which could interfere with the metabolism of the drugs and lead to toxic levels. They should be used during pregnancy and breastfeeding only if the benefit to the mother clearly outweighs the potential risk to the fetus or neonate. In addition, use caution in individuals who work in hot environments because reflex sweating may be blocked, placing the individuals at risk for heat prostration.