2.1 General Administration

Inspect parenteral drug products for particulate matter and discoloration prior to administration, whenever solution and container permit.  Do not administer unless solution is clear and seal is intact.  After initial use, discard unused portion within 24 hours.
Intravenous administration is usually preferred, but subcutaneous, intramuscular, endotracheal, and intraosseous administration are possible. 

2.2 Adult Dosage

Table 1: Recommended Dosage in Adult Patients

2.3 Pediatric Dosage

Table 2: Recommended Dosage in Pediatric Patients

2.4 Dosing in Patients with Ischemic Heart Disease

Limit the total dose of atropine sulfate to 0.03 to 0.04 mg/kg [see Warnings and Precautions (5.2)].

5.1 Hypersensitivity

Atropine may cause anaphylaxis.

5.2 Worsening of Ischemic Heart Disease

In patients with ischemic heart disease, the total dose should be restricted to 2 to 3 mg (maximum 0.03 to 0.04 mg/kg) to avoid atropine-induced tachycardia, increased myocardial oxygen demand and the potential for worsening cardiac ischemia or increasing infarction size.

5.3 Acute Glaucoma

Atropine may precipitate acute glaucoma.

5.4 Pyloric Obstruction

Atropine may convert partial organic pyloric stenosis into complete obstruction.

5.5 Complete Urinary Retention

Atropine may lead to complete urinary retention in patients with prostatic hypertrophy.

5.6 Viscid Plugs

Atropine may cause thickening of bronchial secretions and formation of viscid plugs in patients with chronic lung disease.

5.7 Benzyl Alcohol

The preservative benzyl alcohol has been associated with serious adverse events and death in neonates.  The "gasping syndrome"(characterized by central nervous system depression, metabolic acidosis, gasping respirations, and high levels of benzyl alcohol and its metabolites found in the blood and urine) has been associated with benzyl alcohol dosages >99 mg/kg/day in neonates and low-birth weight infants.  Additional symptoms may include gradual neurological deterioration, seizures, intracranial hemorrhage, hematologic abnormalities, skin breakdown, hepatic and renal failure, hypotension, bradycardia, and cardiovascular collapse.
Although normal therapeutic doses of this product deliver amounts of benzyl alcohol that are substantially lower than those reported in association with the "gasping syndrome", the minimum amount of benzyl alcohol at which toxicity may occur is not known.  Premature and low-birth weight infants may be more likely to develop toxicity.  Practitioners administering this and other medications containing benzyl alcohol should consider the combined daily metabolic load of benzyl alcohol from all sources.

7.1 Mexiletine

Atropine Sulfate Injection decreased the rate of mexiletine absorption without altering the relative oral bioavailability; this delay in mexiletine absorption was reversed by the combination of atropine and intravenous metoclopramide during pretreatment for anesthesia.

8.1 Pregnancy

Risk Summary
Limited available data with Atropine Sulfate Injection use in pregnant women are insufficient to inform a drug associated risk of adverse developmental outcomes (see Data).  There are risks to the mother and fetus associated with untreated severe or life-threatening muscarinic events (see Clinical Considerations).  Animal reproduction studies have not been conducted with Atropine Sulfate Injection.
The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively.
 
Clinical Considerations
Disease-associated maternal and/or embryo/fetal risk
Severe or life-threatening muscarinic events such as acute organophosphate poisoning and symptomatic bradycardia are medical emergencies in pregnancy which can be fatal if left untreated. Life-sustaining therapy for the pregnant woman should not be withheld due to potential concerns regarding the effects of atropine on the fetus.

Data
Human Data
No adequate and well-controlled studies are available regarding use of atropine in pregnant women. In a cohort study of 401 pregnancies in the first trimester and 797 pregnancies in the second or third trimester, atropine use was not associated with an increased risk of congenital malformation. In a surveillance study, 381 newborns were exposed to atropine during the first trimester; 18 major birth defects were observed when 16 were expected. No specific pattern of major birth defects was identified.  In another surveillance study of 50 pregnancies in the first trimester, atropine use was not associated with an increased risk of malformations. Methodological limitations of these observational studies including the inability to control for the dosage and timing of atropine exposure, underlying maternal disease, or concomitant maternal drug use, cannot definitively establish or exclude any drug-associated risk during pregnancy.

8.2 Lactation

Risk Summary
Trace amounts of atropine have been reported in human milk after oral intake. There are no available data on atropine levels in human milk after intravenous injection, the effects on the breastfed infant, or the effects on milk production. The lack of clinical data during lactation precludes a clear determination of the risk of atropine to an infant during lactation.
 

Clinical Considerations
Minimizing exposure
The elimination half-life of atropine is more than doubled in children less than 2 years of age [see Clinical Pharmacology (12.3)]. To minimize potential infant exposure to Atropine Sulfate Injection, a woman may pump and discard her milk for 24 hours after use before resuming to breastfeed her infant.

8.5 Geriatric Use

An evaluation of current literature revealed no clinical experience identifying differences in response between elderly and younger patients.  In general, dose selection for an elderly patient 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.

12.1 Mechanism of Action

Atropine is 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 also may be inhibited by atropine but this occurs less readily than with responses to injected (exogenous) choline esters.

12.2 Pharmacodynamics

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. Atropine exerts a more potent and prolonged effect on heart, intestine and bronchial muscle than scopolamine, but its action on the iris, ciliary body and certain secretory glands is weaker than that of scopolamine. Unlike the latter, atropine in clinical doses does not depress the central nervous system but may stimulate the medulla and higher cerebral centers. Although mild vagal excitation occurs, the increased respiratory rate and (sometimes) 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 also may lessen the degree of partial heart block when vagal activity is an etiologic factor. In some patients 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 in infants and small children.

The effects of intravenous atropine on heart rate (maximum heart rate) and saliva flow (minimum flow) after I.V. administration (rapid, constant infusion over 3 min.) are delayed by 7 to 8 minutes after drug administration and both effects are non-linearly related to the amount of drug in the peripheral compartment. Changes in plasma atropine levels following intramuscular administration (0.5 to 4 mg doses) and heart rate are closely overlapped but the time course of the changes in atropine levels and behavioral impairment indicates that pharmacokinetics is not the primary rate-limiting mechanism for the central nervous system effect of atropine.

12.3 Pharmacokinetics

Absorption
After intramuscular administration, atropine is absorbed with peak concentration occurring at 30 min following injection.  

Effects of exercise:
Exercise following intramuscular administration of atropine significantly increases the absorption of atropine due to increased perfusion in the muscle, with an increase in AUC by approximately 20% and Cmax by approximately 80%.

Distribution
Atropine is distributed throughout the body. Atropine’s plasma protein binding is about 44% and saturable in the 2 to 20 mcg/mL concentration range.
 

Elimination
The pharmacokinetics of atropine is nonlinear after intravenous administration of 0.5 to 4 mg. Atropine disappears from the blood following injection with a plasma half-life of about 2-4 hours.  Much of the drug is destroyed by enzymatic hydrolysis, particularly in the liver, with 13 to 50% is excreted unchanged in the urine.

Metabolism
The major metabolites of atropine are noratropine, atropin-n-oxide, tropine, and tropic acid. The metabolism of atropine is inhibited by organophosphate pesticides.

Specific Populations

Pregnant Women 
Atropine readily crosses the placental barrier and enters the fetal circulation, but is not found in amniotic fluid.
 
Nursing Mother
Traces are found in various secretions, including milk.

Pediatric and Geriatric Patients
The elimination half-life of atropine is more than doubled in children under two years, and the elderly (> 65 years old) compared to other age groups.

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Studies have not been performed to evaluate the carcinogenic or mutagenic potential of atropine or its potential to affect fertility adversely.