Uses of Anticholinergic Drugs

USES

I. As Antisecretory

1. Preanaesthetic medication When irritant general anaesthetics (ether) are used, prior administration of anticholinergics (atropine, hyoscine, glycopyrrolate) is imperative to check increased salivary and tracheobronchial secretions. However, with increasing use of nonirritating anaesthetics (halothane) the requirement has decreased, though atropine may still be employed because halothane sensitizes the heart to NA mediated ventricular arrhythmias which are specially prone to occur during vagal slowing. Atropinic drugs also prevent laryngospasm, not by an action on laryngeal muscles, which are skeletal muscles, but by reducing respiratory secretions that reflexly predispose to laryngospasm. Vasovagal attack during anaesthesia may also be prevented.

2. Peptic ulcer Atropinic drugs decrease gastric secretion (fasting and neurogenic phase, but little effect on gastric phase) and afford symptomatic relief in peptic ulcer, though effective doses always produce side effects. They have now been superseded by H₂ blockers.

3. Pulmonary embolism These drugs benefit by reducing reflex secretions.

4. To check excessive sweating or salivation, e.g. in parkinsonism.

II. As Antispasmodic

§  Intestinal and renal colic, abdominal cramps: symptomatic relief is afforded if there is no mechanical obstruction. Atropine is less effective in biliary colic and is not able to completely counteract biliary spasm due to opiates (nitrates are more effective).

§  Nervous and drug induced diarrhoea, functional diarrhoea, but not effective in infective diarrhoea.

§  Spastic constipation, irritable bowel syndrome.

§  Pylorospasm, gastric hypermotility, gastritis, nervous dyspepsia.

§  To relieve urinary frequency and urgency, enuresis in children. Oxybutynin, tolterodine and flavoxate have demonstrated good efficacy, but dry mouth and other anticholinergic effects are dose limiting.

§  Dysmenorrhoea: These drugs are not very effective.

III. Bronchial Asthma, Asthmatic Bronchitis, COPD

Reflex vagal activity is an important factor in causing bronchoconstriction and increased secretion in chronic bronchitis and COPD, but to a lesser extent in bronchial asthma. Orally administered atropinic drugs are bronchodilators, but less effective than adrenergic drugs. They dry up secretion in the respiratory tract, may lead to its inspissation and plugging of bronchioles resulting in alveolar collapse and predisposition to infection. The mucociliary clearance is also impaired. Inhaled ipratropium bromide has been found to be specially effective in asthmatic bronchitis and COPD, though less so in bronchial asthma. Given by aerosol, it has been shown not to decrease respiratory secretions or to impair mucociliary clearance, and there are few systemic side effects. Thus, it has a place in the management of COPD. Its time course of action makes it more suitable for regular prophylactic use rather than for control of acute attacks. The additive bronchodilator action with adrenergic drugs is utilized to afford relief in acute exacerbation of asthma/COPD by administering a combination of nebulized ipratropium and β₂ agonist through a mask.

IV. As Mydriatic And Cycloplegic

Diagnostic For testing error of refraction, both mydriasis and cycloplegia are needed.

Tropicamide having briefer action has now largely replaced homatropine for this purpose. These drugs do not cause sufficient cycloplegia in children: more potent agents like atropine or hyoscine have to be used. Atropine ointment (1%) applied 24 hours and 2 hours before is often preferred for children below 5 years. Cyclopentolate is an alternative.

To facilitate fundoscopy only mydriasis is needed; a short acting antimuscarinic may be used, but phenylephrine is preferred, especially in the elderly, for fear of precipitating or aggravating glaucoma.

Therapeutic Atropine, because of its long lasting mydriatic-cycloplegic and local anodyne action on cornea, is very valuable in the treatment of iritis, iridocyclitis, choroiditis, keratitis and corneal ulcer. It gives rest to the intraocular muscles and cuts down their painful spasm. Atropinic drugs alternated with a miotic prevent adhesions between iris and lens or iris and cornea and may even break them if already formed.

V. As Cardiac Vagolytic

Atropine is useful in counteracting bradycardia and partial heart block in selected patients where increased vagal tone is responsible, e.g. in some cases of myocardial infarction, digitalis toxicity. However, cardiac arrhythmias or ischaemia may be precipitated in some cases.

VI. For Central Action

Parkinsonism (see No. 31) Central anticholinergics are less effective than levodopa; They are used in mild cases, in drug induced extrapyramidal syndromes and as adjuvant to levodopa.

Motion sickness Hyoscine is the most effective drug for motion sickness. It is particularly valuable in highly susceptible individuals and for vigorous motions. The drug should be given prophylactically (0.2 mg oral), because administration after symptoms have setin is less effective; action lasts 4–6 hours. A transdermal preparation applied behind the pinna 4 hours before journey has been shown to protect for 3 days. Side effects with low oral doses and transdermal medication are few, but sedation and dry mouth may occur. Hyoscine and other anticholinergics are not effective in other types of vomiting.

Hyoscine has been used to produce sedation and amnesia during labour (twilight sleep) and to control maniacal states. It had earned a reputation as a ‘lie detector’ during world war II: its amnesic and depressant action was believed to put the subject ‘off guard’ in the face of sustained interrogation and sleep deprivation, so that he came out with the truth.

VII. To Antagonise Muscarinic Effects Of Drugs And Poisons

Atropine is the specific antidote for anti ChE and early mushroom poisoning (see no. 7). It is also given to block muscarinic actions of neostigmine used for myasthenia gravis, decurarization or cobra envenomation.