Mechanism of Action:

Atropine is commonly classified as an anticholinergic or antiparasympathetic (parasympatholytic) drug. More precisely, however, it is termed an antimuscarinic agent since it antagonizes the muscarine-like actions of acetylcholine and other choline esters.

Atropine inhibits the muscarinic actions of acetylcholine on structures innervated by postganglionic cholinergic nerves, and on smooth muscles, which respond to endogenous acetylcholine but are not so innervated. As with other antimuscarinic agents, the major action of atropine is a competitive or surmountable antagonism, which can be overcome by increasing the concentration of acetylcholine at receptor sites of the effector organ (e.g., by using anticholinesterase agents, which inhibit the enzymatic destruction of acetylcholine). The receptors antagonized by atropine are the peripheral structures that are stimulated or inhibited by muscarine, (i.e., exocrine glands and smooth and cardiac muscle). Responses to postganglionic cholinergic nerve stimulation may also be inhibited by atropine, but this occurs less readily than with responses to injected (exogenous) choline esters.

Pharmacodynamics:

Atropine reduces secretions in the mouth and respiratory passages, relieves the constriction and spasm of the respiratory passages, and may reduce the paralysis of respiration, which results from actions of the toxic agent on the central nervous system. Atropine-induced parasympathetic inhibition may be preceded by a transient phase of stimulation, especially on the heart where small doses first slow the rate before characteristic tachycardia develops due to paralysis of vagal control. Although mild vagal excitation occurs, the increased respiratory rate and occasionally increased depth of respiration produced by atropine are more probably the result of bronchiolar dilatation. Accordingly, atropine is an unreliable respiratory stimulant and large or repeated doses may depress respiration.

Adequate doses of atropine abolish various types of reflex vagal cardiac slowing or asystole. The drug also prevents or abolishes bradycardia or asystole produced by injection of choline esters, anticholinesterase agents or other parasympathomimetic drugs, and cardiac arrest produced by stimulation of the vagus. Atropine may also lessen the degree of partial heart block when vagal activity is an etiologic factor. In some individuals with complete heart block, the idioventricular rate may be accelerated by atropine; in others, the rate is stabilized. Occasionally, a large dose may cause atrioventricular (A-V) block and nodal rhythm.

Atropine in clinical doses counteracts the peripheral dilatation and abrupt decrease in blood pressure produced by choline esters. However, when given by itself, atropine does not exert a striking or uniform effect on blood vessels or blood pressure. Systemic doses slightly raise systolic and lower diastolic pressures and can produce significant postural hypotension. Such doses also slightly increase cardiac output and decrease central venous pressure. Occasionally, therapeutic doses dilate cutaneous blood vessels, particularly in the “blush” area (atropine flush), and may cause atropine “fever” due to suppression of sweat gland activity especially in infants and small children.

Pharmacokinetics:

Atropine is rapidly and well absorbed after intramuscular administration. Atropine disappears rapidly from the blood and is distributed throughout the various body tissues and fluids. Much of the drug is destroyed by enzymatic hydrolysis, particularly in the liver; from 13 to 50% is excreted unchanged in the urine. Traces are found in various secretions, including milk. Atropine readily crosses the placental barrier and enters the fetal circulation.

The approximate Cmax of atropine following 1.67 mg atropine given intramuscularly to adults by the 2 mg ATROPEN® delivery system was 9.6 ± 1.5 (mean ± SEM) ng/mL. The mean Tmax was 3 minutes. The T1/2 of intravenous atropine in pediatric subjects under 2 years is 6.9 ± 3.3 (mean ± SD) hours; in children over 2 years, the T1/2 is 2.5 ± 1.2 (mean ± SD) hours; in adults 16-58 years the T1/2 is 3.0 ± 0.9 (mean ± SD) hours; in geriatric patients 65-75 years it is 10.0 ± 7.3 (mean ± SD) hours. The protein binding of atropine is 14 to 22% in plasma. There are gender differences in the pharmacokinetics of atropine. The AUC(0-inf) and Cmax were 15% higher in females than males. The half-life of atropine is slightly shorter (approximately 20 minutes) in females than males.

General: The desperate condition of the organophosphorous-poisoned individual will generally mask such minor signs and symptoms of atropine treatment as have been noted in normal subjects.

Atropine should be used with caution in individuals with cardiac disease. Conventional systemic doses may precipitate acute glaucoma in susceptible individuals, convert partial pyloric stenosis into complete pyloric obstruction, precipitate urinary retention in individuals with prostatic hypertrophy, or cause inspissation of bronchial secretions and formation of dangerous viscid plugs in individuals with chronic lung disease.

Laboratory Tests: Treatment of organophosphorous nerve agent and insecticide poisoning should be instituted without waiting for the results of laboratory tests. Red blood cell and plasma cholinesterase, and urinary paranitrophenol measurements (in the case of parathion exposure) may be helpful in confirming the diagnosis and following the course of the illness. A reduction in red blood cell cholinesterase concentration to below 50% of normal has been seen only with organophosphorous ester poisoning.

Information for Patients: Appropriate steps must be taken to insure that users understand the indications for and use of the ATROPEN®, including review of symptoms of poisoning and operation of the ATROPEN® (see DOSAGE AND ADMINISTRATION).

Drug Interactions: When atropine and pralidoxime are used together, the signs of atropinization (flushing, mydriasis, tachycardia, dryness of the mouth and nose) may occur earlier than might be expected than when atropine is used alone because pralidoxime may potentiate the effect of atropine.

The following precaution should be kept in mind in the treatment of anticholinesterase poisoning although it does not bear directly on the use of atropine and pralidoxime. Since barbiturates are potentiated by the anticholinesterases, they should be used cautiously in the treatment of convulsions.

Carcinogenesis, Mutagenesis, Impairment of Fertility: No reports regarding the potential of atropine for carcinogenesis, mutagenesis, or impairment of fertility have been published in the literature. Since atropine is indicated for short-term emergency use only, no investigations of these aspects have been conducted.

Pregnancy: Teratogenic Effects - Pregnancy Category C: Adequate animal reproduction studies have not been conducted with atropine. It is not known whether atropine can cause fetal harm when administered to a pregnant woman or if these agents can affect reproductive capacity. Atropine should be administered to a pregnant woman only if clearly needed.

Nursing Mothers: Atropine is found in human milk in trace amounts. Caution should be exercised when atropine is administered to a nursing woman.

Pediatric Use: A review of published literature supports the safety and effectiveness of atropine in the setting of organophosphate insecticide poisoning in all pediatric age groups. The starting dose is 0.05 mg/kg IM every 5 to 20 minutes as needed to provide complete atropinization. (See ADVERSE REACTIONS and DOSAGE AND ADMINISTRATION sections).

Geriatric Use: In general, dose selection for an elderly individual should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Cardiovascular: Sinus tachycardia, supraventricular tachycardia, junctional tachycardia, ventricular tachycardia, bradycardia, palpitations, ventricular arrhythmia, ventricular flutter, ventricular fibrillation, atrial arrhythmia, atrial fibrillation, atrial ectopic beats, ventricular premature contractions, bigeminal beats, trigeminal beats, nodal extrasystole, ventricular extrasystole, supraventricular extrasystole, asystole, cardiac syncope, prolongation of sinus node recovery time, cardiac dilation, left ventricular failure, myocardial infarction, intermittent nodal rhythm (no P wave), prolonged P wave, shortened PR segment, R on T phenomenon, shortened RT duration, widening and flattening of QRS complex, prolonged QT interval, flattening of T wave, repolarization abnormalities, altered ST-T waves, retrograde conduction, transient AV dissociation, increased blood pressure, decreased blood pressure, labile blood pressure, weak or impalpable peripheral pulses.

Eye: Mydriasis, blurred vision, pupils poorly reactive to light, photophobia, decreased contrast sensitivity, decreased visual acuity, decreased accommodation, cycloplegia, strabismus, heterophoria, cyclophoria, acute angle closure glaucoma, conjunctivitis, keratoconjunctivitis sicca, blindness, tearing, dry eyes/dry conjunctiva, irritated eyes, crusting of eyelid, blepharitis.

Gastrointestinal: Nausea, abdominal pain, paralytic ileus, decreased bowel sounds, distended abdomen, vomiting, delayed gastric emptying, decreased food absorption, dysphagia.

General: Hyperpyrexia, lethargy, somnolence, chest pain, excessive thirst, weakness, syncope, insomnia, tongue chewing, dehydration, feeling hot, injection site reaction.

Immunologic: Anaphylactic reaction.

Special Investigations: Leukocytosis, hyponatremia, elevated BUN, elevated hemoglobin, elevated erythrocytes, low hemoglobin, hypoglycemia, hyperglycemia, hypokalemia, increase in photic stimulation on EEG, signs of drowsiness on EEG, runs of alpha waves on EEG, alpha waves (EEG) blocked upon opening eyes.

Metabolic: Failure to feed.

Central Nervous System: Ataxia, hallucinations (visual or aural), seizures (generally tonic-clonic), abnormal movements, coma, confusion, stupor, dizziness, amnesia, headache, diminished tendon reflexes, hyperreflexia, muscle twitching, opisthotnos, Babinski's reflex/Chaddock's reflex, hypertonia, dysmetria, muscle clonus, sensation of intoxication, difficulty concentrating, vertigo, dysarthria.

Psychiatric: Agitation, restlessness, delirium, paranoia, anxiety, mental disorders, mania, withdrawn behavior, behavior changes.

Genitourinary: Difficulty in micturation, urine urgency, distended urinary bladder, urine retention, bed-wetting.

Pulmonary: Tachypnea, slow respirations, shallow respirations, breathing difficulty, labored respirations, inspiratory stridor, laryngitis, laryngospasm, pulmonary edema, respiratory failure, subcostal recession.

Dermatologic: Dry mucous membranes, dry warm skin, flushed skin, oral lesions, dermatitis, petechiae, rash, macular rash, papular rash, maculopapular rash, scarlatiniform rash, erythematous rash, sweating/moist skin, cold skin, cyanosed skin, salivation.

Symptoms:

Serious overdosage with atropine is characterized by widespread paralysis of parasympathetically innervated organs. Dry mucous membranes, widely dilated and nonresponsive pupils, tachycardia, fever and cutaneous flush are especially prominent, as are mental and neurological symptoms. Disorientation, mania, hallucinations, gait disturbances and symptoms may last 48 hours or longer. In instances of severe intoxication, respiratory depression, coma, circulatory collapse and death may occur.

The fatal dose of atropine is not known. In the treatment of organophosphorous poisoning, cumulative doses of approximately 2300-3300 mg or more have been administered over several days to 4-5 weeks. In children, medical literature published prior to 1951 reports four deaths, all in patients 10 months to 3 years of age, and all associated with atropine eye drops or ointment. Total estimated ophthalmic doses were 1.6, 2, 4, and 18 mg given as a single dose (2 mg) or over 1-2 days. Review of current published literature since 1950 identified no pediatric deaths associated with atropine. The few deaths in adults were generally seen using typical clinical doses of atropine often in the setting of bradycardia associated with an acute myocardial infarction.

With a dose as low as 0.5 mg, undesirable symptoms or responses of overdosage may occur. These increase in severity and extent with larger doses of the drug (excitement, hallucinations, delirium and coma). Extreme hyperthermia in a newborn has been reported with as little as 0.065 mg orally. However, in the presence of organophosphorous poisoning, much higher doses of atropine appear to be tolerated and required for optimal therapy.

Treatment:

Supportive treatment should be administered as indicated. If respiration is depressed, artificial respiration with oxygen is necessary. Ice bags, alcohol sponges or a hypothermia blanket may be required to reduce fever, especially in children. Catheterization may be necessary if urinary retention occurs. Since atropine elimination takes place through the kidney, output must be maintained and increased if possible, however, dialysis has not been shown to be helpful in overdose situations. Intravenous fluids may be indicated. Because of the affected person's photophobia, the room should be darkened.

In the event of toxic overdosage, a short-acting barbiturate or diazepam may be given as needed to control marked excitement and convulsions. Large doses for sedation should be avoided because central depressant action may coincide with the depression occurring late in atropine poisoning. Central stimulants are not recommended. Physostigmine, given as an atropine antidote by slow intravenous injection of 1 to 4 mg (0.5 to 1.0 mg in children), rapidly abolishes delirium and coma caused by large doses of atropine in most situations. Since physostigmine has a short duration of action, the patient may again lapse into coma after one or two hours and repeated doses are likely to be required. Neostigmine, pilocarpine and methacholine are of little real benefit, since they do not penetrate the blood-brain barrier.

Treatment of MILD SYMPTOMS:

One (1) ATROPEN® is recommended if two or more MILD symptoms of nerve agent (nerve gas) or insecticide exposure appear in situations where exposure is known or suspected.

Two (2) additional ATROPEN® injections given in rapid succession are recommended 10 minutes after receiving the first ATROPEN® injection if the victim has any of the SEVERE symptoms listed below. If possible, a person other than the victim should administer the second and third ATROPEN® injections.

Treatment of SEVERE SYMPTOMS:

If a victim is encountered who is either unconscious or has any of the SEVERE symptoms listed below, immediately administer three (3) ATROPEN® injections into the victim's mid-lateral thigh in rapid succession using the appropriate weight-based ATROPEN® dose.

All victims should be evacuated immediately from the contaminated environment. Medical help should be sought immediately. Protective masks and clothing should be used when available. Decontamination procedures should be undertaken as soon as possible. If dermal exposure has occurred, clothing should be removed and the hair and skin washed thoroughly with sodium bicarbonate or alcohol as soon as possible.

Emergency care of the severely poisoned individual should include removal of oral and bronchial secretions, maintenance of a patent airway, supplemental oxygen and, if necessary, artificial ventilation. In general, atropine should not be used until cyanosis has been overcome since atropine may produce ventricular fibrillation and possible seizures in the presence of hypoxia.

Pralidoxime (if used) is most effective if administered immediately or soon after the poisoning. Generally, little is accomplished if pralidoxime is given more than 36 hours after termination of exposure unless the poison is known to age slowly or re-exposure is possible, such as in delayed continuing gastrointestinal absorption of ingested poisons. Fatal relapses, thought to be due to delayed absorption, have been reported after initial improvement. Continued administration for several days may be useful in such patients.

Close supervision of all moderately to severely poisoned patients is indicated for at least 48 to 72 hours.

An anticonvulsant such as diazepam may be administered to treat convulsions if suspected in the unconscious individual. The effects of nerve agents and some insecticides can mask the motor signs of a seizure.

IMPORTANT: PHYSICIANS AND/OR OTHER MEDICAL PERSONNEL ASSISTING EVACUATED VICTIMS OF NERVE AGENTS AND INSECTICIDE POISONING SHOULD AVOID EXPOSING THEMSELVES TO CONTAMINATION BY THE VICTIM'S CLOTHING. AGGRESSIVE AND SAFE DECONTAMINATION IS STRONGLY SUGGESTED.

Instructions for administering ATROPEN® (please refer to the illustrated dose specific Self Aid and Caregiver Directions for Use at the end of this package insert):

Warning: Giving additional ATROPEN®injections by mistake in the absence of actual nerve agent or insecticide poisoning may cause an overdose of atropine which could result in temporary incapacitation (inability to walk properly, see clearly or think clearly for several or more hours). Patients with cardiac disease may be at risk for serious adverse events, including death.