Atropine binds to and inhibit muscarinic acetylcholine receptors, producing a wide range of anticholinergic effects. Atropine is an anticholinergic agent which competitively blocks the muscarinic receptors in peripheral tissues such as the heart, intestines, bronchial muscles, iris and secretory glands. Some central stimulation may occur. Atropine abolishes bradycardia and reduces heart block due to vagal activity. Smooth muscles in the bronchi and gut are relaxed while glandular secretions are reduced. It also has mydriatic and cycloplegic effect.

In cardiovascular disorders: Typical initial doses are in the range of 0.5 to 1.0 mg intravenously. In less severe cases doses may be repeated, as necessary, upto a total dose of 0.03 mg per kg body-weight (about 2 mg); suggested dosage intervals have ranged from 3 to 5 minutes to 1 to 2 hours. In severe instances, as in asystole, a total dose of 0.04 mg per kg (about 3 mg) may be given; some authorities have recommended that the total amount should be given in three divided doses of 1 mg at 3 to 5 minute intervals whereas others consider that 3 mg should be given as a single dose.

As anaesthetic premedication: 300 to 600 mcg may be given by subcutaneous (S.C.) or intramuscular (I.M.) injection, usually 30 to 60 minutes before anaesthesia. Alternatively 300 to 600 mcg may be given intravenously immediately before induction of anaesthesia. It may also be given in combination with upto 10 mg morphine sulphate by S.C. or I.M. injection about an hour before anaesthesia.

Suitable paediatric premedication doses are:

• Children weighing upto 3 kg: 100 mcg subcutaneously.
• Children weighing 7-9 kg: 200 mcg subcutaneously.
• Children weighing 12-16 kg: 300 mcg subcutaneously.
• Children weighing 20-27 kg: 400 mcg subcutaneously.
• Children weighing 32 kg: 500 mcg subcutaneously.
• Children weighing 41 kg: 600 mcg subcutaneously.

In anticholinesterase and mushroom poisoning: It is used in very large doses, e.g. beginning with a dose of 2 mg intravenously or intramuscularly and repeating every 5 to 15 minutes as necessary until signs and symptoms disappear. Doses of up to 100 mg may be needed in the first 24 hours, and lower oral doses should be continued to prevent reappearance of symptoms.

For control of muscarinic side-effects of neostigmine: 0.6 to 1.2 mg by intravenous injection in conjunction with neostigmine methylsulphate.

Infants and children are particularly susceptible to toxic effects of atropine.

Peripheral and central nervous system anticholinergic action is additive with other drugs which have anticholinergic activity for example, tricyclic antidepressants, other antispasmodics and antiparkinsonian drugs, some antihistamines, phenothiazines, disopyramide and quinidine. By delaying gastric emptying, atropine may delay the onset of action of other drugs and in some cases increase absorption. Addition of metoclopramide accentuates the reduction of lower oesophageal pressure produced by atropine premedication, and may thus protect against aspiration of gastric contents.

It is contraindicated in patients with glaucoma, chronic lung disease, unstable cardiac rhythm, prostatic hypertrophy, reflux oesophagitis, paralytic ileus or pyloric stenosis, and generally, in the elderly.

Dryness of the mouth with difficulty in swallowing and talking, thirst, reduced bronchial secretions, dilatation of the pupils (mydriasis) with loss of accomodation (cycloplegia) and photophobia, flushing, dryness of skin, transient bradycardia followed by tachycardia with palpitations and arrhythmias, difficulty in micturition, as well as reduction in the tone and motility of GIT leading to constipation. Occasionally vomiting may also occur.

It has negligible effects on the human uterus and is not teratogenic. Small quantities of atropine appears in breast milk when the drug is given to lactating mothers. It has also been reported to impair milk production, although this is not conclusively documented.

It should be used with caution in children, and in geriatric patients, who may be more susceptible to its adverse effects. It is generally advisable to be cautious in giving atropine to any patient with diarrhoea. Due to the risk of provoking hyperpyrexia atropine should not be given to patients, especially children when the ambient temperature is high. It should also be used cautiously in patients with fever. Persons with Down's syndrome appear to have an increased susceptibility to the actions of atropine. It should be used with caution in conditions characterised by tachycardia such as thyrotoxicosis, heart failure, and in cardiac surgery, where it may further accelerate the heart rate. Care is required in patients with acute myocardial infarction as ischaemia and infarction may be made worse. It should be given with care to patients with hypertension.

Atropine may cause mental confusion, especially in the elderly. Reduced bronchial secretion caused by systemic administration of atropine may be associated with the formation of mucous plugs.

In the treatment of parkinsonism, increases in dosage and transfer to other forms of treatment should be gradual and antimuscarinic agents should not be withdrawn abruptly. Minor reactions may be controlled by reducing the dose until tolerance has developed.

Keep below 25°C temperature, away from light & moisture. Keep out of the reach of children.