McKenna's Pharmacology for Nursing, 2e

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

Safe medication administration

Prototype summary: Atropine Indications: To decrease secretions before surgery, treatment of parkinsonism, restoration of cardiac rate and arterial pressure following vagal stimulation, relief of bradycardia and syncope due to hyperactive carotid sinus reflex, relief of pylorospasm, relaxation of the spasm of biliary and ureteral colic and bronchospasm, control of crying and laughing episodes associated with brain lesions, relaxation of uterine hypertonicity, management of peptic ulcer, control of rhinorrhoea associated with hay fever, antidote for cholinergic overdose and poisoning from various mushrooms. Actions: Competitively blocks acetylcholine muscarinic receptor sites, blocking the effects of the parasympathetic nervous system. SC Varies 4 hours Topical 5–10 mins 30–40 mins 7–14 days T 1/2 : 2.5 hours, with metabolism in the liver and excretion in the urine. Adverse effects: Blurred vision, mydriasis, cycloplegia, photophobia, palpitations, bradycardia, dry mouth, altered taste perception, urinary hesitancy and retention, decreased sweating and predisposition to heat prostration (see Focus on safe medication administration for more information about atropine toxicity). 1–2 hours Pharmacokinetics: Route Onset Peak Duration IM 10–15 mins 30 mins IV Immediate 2–4 mins 4 hours 4 hours

such combinations must be used, the person should be monitored closely and dose adjustments made. People should be advised to avoid over-the-counter products that contain these drugs. The effectiveness of phenothiazines decreases if they are combined with anticholinergic drugs and the risk of paralytic ileus increases. This combination should be avoided. Anticholinergics also may interact with certain herbal therapies (see Box 33.2). immediate gastric lavage should be done to limit absorption. Physostigmine can be used as an antidote, however it is controversial. It can result in serious adverse effects and is only recommended in life threatening situations. A slow intravenous injection of 0.5 to 4 mg (depending on the size of the individual) usually reverses the delirium and coma of atropine toxicity. Physostigmine is metabolised rapidly, so the injection may need to be repeated every 1 to 2 hours until the atropine has been cleared from the system. Diazepam is the drug of choice if an anticonvulsant is needed. Cool baths and alcohol sponging may relieve the fever and hot skin. In extreme cases, respiratory support may be needed. It is important to remember that the half-life of atropine is 2.5 hours; at extremely high doses, several hours may be needed to clear the atropine from the body. Atropine toxicity Although atropine is used in a large variety of clinical settings (see Table 33.1 for usual indications), this drug can also be a poison, causing severe toxicity. Because it is found in many natural products, including the belladonna plant, and may be present in herbal or alternative therapy products, atropine toxicity can occur inadvertently. Atropine toxicity should be considered whenever a person receiving an anticholinergic drug presents with a sudden onset of bizarre mental and neurological symptoms. Toxicity is dose related and usually progresses as follows: 0.5 mg atropine: slight cardiac slowing, dryness of mouth, inhibition of sweating 1.0 mg atropine: definite mouth and throat dryness, thirst, rapid heart rate, pupil dilation 2.0 mg atropine: rapid heart rate, palpitations; marked mouth dryness; dilated pupils; some blurring of vision 5.0 mg atropine: all of the foregoing and marked speech disturbances; difficulty swallowing; restlessness, fatigue and headache; dry and hot skin; difficulty voiding; reduced intestinal peristalsis 10.0 mg atropine: all of the foregoing symptoms, more marked; pulse rapid and weak; iris nearly gone; vision blurred; skin flushed, hot, dry and scarlet; ataxia; restlessness and excitement; hallucinations; delirium and coma Treatment is as follows. If the poison was taken orally,

The risk of anticholinergic effects can be exacerbated if anticholinergic agents are combined with burdock, rosemary or turmeric used as herbal therapy. Advise people who use herbal therapies to avoid these combinations. Herbal and alternative therapies BOX 33.2

■■ At cholinergic receptor sites, anticholinergic drugs block the effects of acetylcholine. Because they block the effects of the parasympathetic nervous system, they are also known as parasympatholytic drugs. ■■ When the parasympathetic system is blocked, the pupils dilate, the heart rate rises, and GI activity and urinary bladder tone and function decrease. KEY POINTS