Action

Inhibits acetylcholine at parasympathetic neuroeffector junction of smooth muscle and cardiac muscle, blocking sinoatrial (SA) and atrioventricular (AV) nodes. These actions increase impulse conduction and raise heart rate. In ophthalmic use, blocks cholinergic stimulation to iris and ciliary bodies, causing pupillary dilation and accommodation paralysis.

Availability

Injection: 0.05 mg/ml, 0.1 mg/ml, 0.3 mg/ml, 0.4 mg/ml, 0.5 mg/ml, 0.8 mg/ml, 1 mg/ml

Ophthalmic solution: 0.5%, 1%, 2%

Tablets: 0.4 mg

Indications and dosages

➣ Bradyarrhythmias, symptomatic bradycardia

Adults: 0.5 to 1 mg by I.V. push repeated q 3 to 5 minutes as needed, to a maximum dosage of 2 mg

Children: 0.01 mg/kg I.V. to a maximum dosage of 0.4 mg or 0.3 mg/m². May repeat I.V. dose q 4 to 6 hours.

➣ Antidote for anticholinesterase insecticide poisoning

Adults: 2 to 3 mg I.V. repeated q 5 to 10 minutes until symptoms disappear or a toxic level is reached. For severe poisoning, 6 mg q hour.

Children: 0.05 mg/kg I.M. or I.V. repeated q every 10 to 30 minutes until symptoms disappear or a toxic level is reached

➣ Preoperatively to diminish secretions and block cardiac vagal reflexes

Adults and children weighing more than 40.8 kg (90 lb): 0.4 to 0.6 mg I.M., I.V., or subcutaneously 30 to 60 minutes before anesthesia

Children weighing 29.5 to 40.8 kg (65 to 90 lb): 0.4 mg I.M., I.V., or subcutaneously 30 to 60 minutes before anesthesia

Children weighing 18.1 to 29.5 kg (40 to 65 lb): 0.3 mg I.M., I.V., or subcutaneously 30 to 60 minutes before anesthesia

Children weighing 10.9 to 18.1 kg (24 to 40 lb): 0.2 mg I.M., I.V., or subcutaneously 30 to 60 minutes before anesthesia

Children weighing 7.3 to 10.9 kg (16 to 24 lb): 0.15 mg I.M., I.V., or subcutaneously 30 to 60 minutes before anesthesia

Children weighing 3.2 to 7.3 kg (7 to 16 lb): 0.1 mg I.M., I.V., or subcutaneously 30 to 60 minutes before anesthesia

➣ Peptic ulcer disease, functional GI disorders (such as hypersecretory states)

Adults: 0.4 to 0.6 mg P.O. q 4 to 6 hours

Children: 0.01 mg/kg or 0.3/m² P.O. q 4 to 6 hours

➣ Parkinsonism

Adults: 0.1 to 0.25 mg P.O. q.i.d.

➣ Antidote for muscarine-induced mushroom toxicity

Adults: 1 to 2 mg/hour I.M. or I.V. until respiratory function improves

➣ Pupillary dilation in acute inflammatory conditions of iris and uveal tract

Adults: Instill one or two drops of 0.5% or 1% solution into eye(s) up to q.i.d.

Children: Instill one or two drops of 0.5% solution into eye(s) up to t.i.d.

➣ To produce mydriasis and cycloplegia for refraction

Adults: Instill one or two drops of 1% solution into eye(s) 1 hour before refraction.

Children: Instill one or two drops of 0.5% solution into eye(s) b.i.d. for 1 to 3 days before examination.

Off-label uses

• Cholinergic-mediated bronchial asthma

Contraindications

• Hypersensitivity to drug or other belladonna alkaloids

• Acute narrow-angle glaucoma

• Adhesions between iris and lens (ophthalmic form)

• Obstructive GI tract disease

• Unstable cardiovascular status

• Asthma

• Myasthenia gravis

• Thyrotoxicosis

• Infants ages 3 months and younger

Precautions

Use cautiously in:

• chronic renal, hepatic, pulmonary, or cardiac disease

• intra-abdominal infection, prostatic hypertrophy

• elderly patients

• pregnant or breastfeeding patients

• children.

Administration

• For I.V. dose, infuse directly into large vein or I.V. tubing over at least 1 minute.

• Be aware that doses of 0.5 mg may cause paradoxical bradycardia because of central or peripheral parasympathomimetic effects of low doses in adults.

• Don't administer oral dose within 1 hour of giving antacids.

• Be aware that patients with Down syndrome may be unusually sensitive to drug.

Adverse effects

CNS: headache, restlessness, ataxia, disorientation, delirium, insomnia, dizziness, drowsiness, agitation, nervousness, confusion, excitement

CV: palpitations, bradycardia, tachycardia

EENT: photophobia, blurred vision, increased intraocular pressure, mydriasis, cycloplegia, nasal congestion

GI: nausea, vomiting, constipation, bloating, dyspepsia, ileus, abdominal distention (in infants), dysphagia, dry mouth

GU: urinary retention, urinary hesitancy, impotence

Skin: decreased sweating, flushing, urticaria, dry skin

Other: thirst, anaphylaxis

Interactions

Drug-drug. Amantadine, antiarrhythmics, anticholinergics, antihistamines, antiparkinsonian drugs, glutethimide, meperidine, muscle relaxants, phenothiazines, tricyclic antidepressants: increased atropine effects

Antacids, antidiarrheals: decreased atropine absorption

Antimyasthenics: decreased intestinal motility

Cyclopropane: ventricular arrhythmias Ketoconazole, levodopa: decreased absorption of these drugs

Metoclopramide: decreased effect of atropine on GI motility

Potassium chloride wax-matrix tablets: increased severity of mucosal lesions

Drug-herbs. Jaborandi tree, pill-bearing spurge: decreased drug effect

Jimsonweed: changes in cardiovascular function

Squaw vine: reduced metabolic breakdown of drug

Drug-behaviors. Sun exposure: increased risk of photophobia

Patient monitoring

See Watch closely for signs and symptoms of anaphylaxis.

• Monitor heart rate for bradycardia or tachycardia.

• Evaluate fluid intake and output.

• Assess for urine retention or urinary hesitancy.

• Monitor for signs and symptoms of glaucoma.

Patient teaching

See Instruct patient to immediately report allergic response.

See Inform patient that headache, eye pain, and blurred vision may signal glaucoma. Tell him to report these symptoms at once.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration, alertness, and vision.

• Encourage patient to establish an effective bedtime routine to minimize insomnia.

• Tell patient to apply pressure to inside corner of eye during instillation of ophthalmic solution and for 1 to 2 minutes afterward.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, herbs, and behaviors mentioned above.