ATROPINE SULFATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ATROPINE SULFATE (ATROPINE SULFATE).
Competitive antagonist of muscarinic acetylcholine receptors (M1, M2, M3, M4, M5), blocking the effects of acetylcholine at parasympathetic postganglionic junctions. Increases heart rate, reduces exocrine secretions, relaxes smooth muscle in GI and GU tracts, and dilates pupils.
| Metabolism | Primarily metabolized by hepatic cytochrome P450 enzymes (CYP3A4 and CYP2D6) via oxidative deamination and glucuronidation. Also undergoes hydrolysis by tissue esterases. |
| Excretion | Renal excretion of unchanged drug and metabolites; ~50% excreted unchanged in urine; remainder as inactive metabolites (tropine, tropic acid); biliary/fecal excretion minor. |
| Half-life | Terminal elimination half-life approximately 2-4 hours in adults; prolonged in elderly and infants; clinically significant due to potential accumulation with repeated dosing. |
| Protein binding | Approximately 50% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | 2-4 L/kg; indicates extensive tissue distribution with high affinity for tissues (e.g., salivary glands, smooth muscle, cardiac tissue). |
| Bioavailability | Oral: 10-25% due to first-pass metabolism and poor absorption; IM/IV: 100%. |
| Onset of Action | IV: <1 minute; IM: 2-3 minutes; Subcutaneous: 2-5 minutes; Oral: 30-60 minutes; Ophthalmic: 5-10 minutes for mydriasis. |
| Duration of Action | Cardiac effects: 15-30 minutes post IV; Antisialagogue: up to 4 hours; Mydriasis: 7-14 days with ophthalmic administration; Cycloplegia: 5-10 days. |
0.5 to 1 mg intravenously or intramuscularly every 3 to 5 minutes as needed, up to a total of 3 mg (3 doses) for bradycardia; 0.5 to 1 mg subcutaneously, intramuscularly, or intravenously every 4 to 6 hours for antisecretory effects; 1 to 2 mg intravenously every 5 minutes for organophosphate poisoning.
| Dosage form | SOLUTION |
| Renal impairment | No specific dose adjustment recommended for renal impairment; use with caution in severe renal failure. |
| Liver impairment | No specific dose adjustment recommended for hepatic impairment; use with caution in severe liver disease. |
| Pediatric use | 0.01 to 0.02 mg/kg intravenously every 3 to 5 minutes as needed for bradycardia, maximum single dose 0.5 mg in children and 1 mg in adolescents; 0.01 mg/kg subcutaneously every 4 to 6 hours for antisecretory effects; 0.05 to 0.1 mg/kg intramuscularly or intravenously every 5 minutes for organophosphate poisoning. |
| Geriatric use | Initiate at lower end of dosing range due to increased sensitivity; reduce dose for bradycardia to 0.5 mg intravenously every 5 minutes as needed; monitor for central anticholinergic effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ATROPINE SULFATE (ATROPINE SULFATE).
| Breastfeeding | Atropine is excreted into breast milk in small amounts; M/P ratio is approximately 0.5. Theoretical risk of anticholinergic effects in the infant (tachycardia, constipation) with high maternal doses. Compatible with breastfeeding when used at standard doses; monitor infant for unusual symptoms. |
| Teratogenic Risk | First trimester: No evidence of teratogenicity in humans; animal studies show no fetal harm at therapeutic doses. Second and third trimesters: May cause fetal tachycardia and reduced amniotic fluid production with chronic use. Near term: Risk of neonatal meconium ileus and transient autonomic instability. |
■ FDA Black Box Warning
Not indicated for use as an antiemetic in children due to risk of paradoxical reactions and CNS effects.
| Common Effects | Stinging sensation High blood pressure |
| Serious Effects |
["Hypersensitivity to atropine or any component of the formulation","Angle-closure glaucoma (unless used for pre-surgical mydriasis under specialist care)","Tachycardia due to thyrotoxicosis or cardiac insufficiency","Obstructive gastrointestinal diseases (e.g., paralytic ileus, pyloric stenosis)","Obstructive uropathy (e.g., prostatic hyperplasia with urinary retention)","Severe ulcerative colitis (risk of toxic megacolon)","Myasthenia gravis (unless used to reverse anticholinesterase agents under controlled conditions)"]
| Precautions | ["Use with caution in patients with coronary artery disease (may increase myocardial oxygen demand)","May aggravate conditions such as glaucoma (angle-closure), pyloric stenosis, prostatic hyperplasia, or myasthenia gravis","Risk of heat stroke due to inhibition of sweating, especially in high ambient temperatures","In children, may cause paradoxical excitement, restlessness, or CNS depression","Avoid in patients with known hypersensitivity to anticholinergics","May cause blurred vision and photophobia (caution driving or operating machinery)"] |
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| Fetal Monitoring | Maternal: Heart rate, urinary retention, bowel sounds, and CNS effects (confusion, hallucinations). Fetal: Heart rate monitoring during chronic use or high doses; ultrasound for amniotic fluid volume if used long-term. |
| Fertility Effects | Animal studies show no impairment of fertility. Human data lacking; theoretical risk from anticholinergic effects on reproductive tract secretions. |
| Food/Dietary | No significant food interactions. However, atropine may decrease GI motility, potentially causing constipation; a high-fiber diet and adequate fluid intake may help. Avoid excessive alcohol consumption. |
| Clinical Pearls | Atropine is an anticholinergic agent used primarily for bradycardia, as an antisialagogue, and for organophosphate poisoning. It crosses the blood-brain barrier and can cause central anticholinergic syndrome. In pediatrics, the dose for bradycardia is 0.02 mg/kg with a minimum dose of 0.1 mg to avoid paradoxical bradycardia. For organophosphate poisoning, large doses may be required (titrated to drying of secretions). Atropine is contraindicated in narrow-angle glaucoma, myasthenia gravis, and obstructive GI disorders. |
| Patient Advice | May cause blurred vision, dizziness, and dry mouth; avoid driving until effects resolve. · Use caution in hot weather as atropine decreases sweating and can lead to heat stroke. · Avoid alcohol and other CNS depressants as they may exacerbate side effects. · If using for bradycardia, seek emergency medical attention for symptoms like fainting or chest pain. · Do not take with other anticholinergic medications without consulting your doctor. |