Side Effects and Toxicity

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Chapter: Essential pharmacology : Anticholinergic Drugs And Drugs Acting On Autonomic Ganglia

Side effects are quite common with the use of atropine and its congeners; are due to facets of its action other than for which it is being used. They cause inconvenience but are rarely serious.


SIDE EFFECTS AND TOXICITY

 

Side effects are quite common with the use of atropine and its congeners; are due to facets of its action other than for which it is being used. They cause inconvenience but are rarely serious.

 

Belladonna poisoning may occur due to drug overdose or consumption of seeds and berries of belladonna/datura plant. Children are highly susceptible. Manifestations are due to exaggerated pharmacological actions.

 

Dry mouth, difficulty in swallowing and talking. Dry, flushed and hot skin (especially over face and neck), fever, difficulty in micturition, decreased bowel sounds, a scarlet rash may appear. Dilated pupil, photophobia, blurring of near vision, palpitation.

 

Excitement, psychotic behaviour, ataxia, delirium, dreadful visual hallucinations.

Hypotension, weak and rapid pulse, cardiovascular collapse with respiratory depression.

Convulsions and coma occur only in severe poisoning.

 

Diagnosis Methacholine 5 mg or neostigmine 1 mg s.c. fails to induce typical muscarinic effects.

 

Treatment If poison has been ingested, gastric lavage should be done with tannic acid (KMnO4 is ineffective in oxidizing atropine). The patient should be kept in a dark quiet room. Cold sponging or ice bags are applied for reducing body temperature. Physostigmine 1–3 mg s.c. or i.v. antagonises both central and peripheral effects, but has been found to produce hypotension and arrhythmias in some cases. As such, its utility is controversial. Neostigmine does not antagonise the central effects.

 

Other general measures (maintenance of blood volume, assisted respiration, diazepam to control convulsions) should be taken as appropriate.

 

Contraindications 


Atropinic drugs are absolutely contraindicated in individuals with a narrow iridocorneal angle—may precipitate acute congestive glaucoma. However, marked rise in intraocular tension is rare in patients with wide angle glaucoma.

 

Caution is advocated in elderly males with prostatic hypertrophy—urinary retention can occur.

 

 

Interactions

 

§  Absorption of most drugs is slowed because atropine delays gastric emptying. This results in slower absorption and greater peripheral degradation of levodopa—less of it reaches the brain. This does not occur when a peripheral decarboxylase inhibitor is combined.

 

§  On the other hand, extent of digoxin and tetracycline absorption may be increased due to longer transit time in the g.i.t.

§  Antacids interfere with absorption of anticholinergics.

§  Antihistaminics, tricyclic antidepressants, phenothiazines, disopyramide, pethidine

§  have anticholinergic property—additive side effects occur with atropinic drugs.

§  MAO inhibitors interfere with metabolism of anticholinergic antiparkinsonian drugs — delirium may occur.

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