ATROPINE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ATROPINE (ATROPINE).
Competitive antagonist of muscarinic acetylcholine receptors (M1, M2, M3, M4, M5), blocking the effects of acetylcholine and other cholinergic agonists. Inhibits vagal activity, increases heart rate, reduces secretions, and relaxes smooth muscle.
| Metabolism | Primarily hepatic via enzymatic hydrolysis; approximately 30-50% excreted unchanged in urine. Elimination half-life is around 2-4 hours. |
| Excretion | Renal (30-50% unchanged; remainder as inactive metabolites via hydrolysis and glucuronidation); 50-70% of a dose renally excreted as metabolites; <5% fecal |
| Half-life | 2-4 hours (terminal); prolonged in elderly and neonates; clinically requires dosing every 4-6 hours |
| Protein binding | 14-22% (primarily albumin) |
| Volume of Distribution | 2-4 L/kg; indicates extensive tissue distribution, particularly in CNS |
| Bioavailability | Oral: 10-25% (extensive first-pass metabolism) |
| Onset of Action | IV: <1 minute; IM: 5-10 minutes; Oral: 30-60 minutes; Ophthalmic: 5-10 minutes for cycloplegia |
| Duration of Action | IV/IM: 4-6 hours; Oral: 4-6 hours; Ophthalmic: up to 7 days for mydriasis and cycloplegia |
| Molecular Weight | 289.37 |
0.5-1 mg IV/IM/SC every 3-5 minutes as needed, up to a total of 3 mg (adults). For preoperative use, 0.4-0.6 mg IM/IV 30-60 minutes before anesthesia.
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for renal impairment. Atropine is primarily metabolized in the liver and excreted in urine as inactive metabolites; however, no GFR-based modifications are recommended. |
| Liver impairment | No specific dose adjustment recommended for hepatic impairment (Child-Pugh class A, B, or C). Use with caution in severe liver disease due to potential increased sensitivity. |
| Pediatric use | 0.01-0.02 mg/kg IV/IM/SC per dose, minimum 0.1 mg, maximum 0.5 mg per dose (children). For preoperative use, 0.01-0.02 mg/kg IM/IV (max 0.4 mg). For bradycardia, 0.02 mg/kg IV, may repeat every 5 minutes, max total 1 mg in adolescents. |
| Geriatric use | Elderly patients may be more sensitive to anticholinergic effects (e.g., confusion, urinary retention, constipation). Lower initial doses (e.g., 0.3-0.5 mg IV) are recommended. Titrate carefully and monitor for adverse effects. |
| 1st trimester | Crosses placenta; no adequate well-controlled studies in pregnant women. Use only if benefit outweighs risk. May cause fetal tachycardia and decreased amniotic fluid. |
| 2nd trimester | Crosses placenta; no adequate well-controlled studies. Monitor fetal heart rate. Use with caution. |
| 3rd trimester | Crosses placenta; may cause neonatal tachycardia, irritability, and delayed meconium passage. Avoid near term if possible. |
Clinical note
Comprehensive clinical and safety monograph for ATROPINE (ATROPINE).
| Placental transfer | Atropine crosses the placenta by passive diffusion. Peak fetal levels occur within 30 minutes of maternal IV administration; ratio of fetal to maternal concentration is approximately 0.93. Found in fetal tissues and amniotic fluid. |
| Breastfeeding | Atropine is excreted into breast milk in small amounts. No adverse effects reported in infants. Use with caution, especially in neonates due to potential anticholinergic effects. Monitor infant for excessive dryness, constipation, or tachycardia. |
■ FDA Black Box Warning
Not applicable.
| Common Effects | Stinging sensation High blood pressure |
| Serious Effects |
Hypersensitivity to atropine or any componentAngle-closure glaucoma (unless surgically treated)Obstructive gastrointestinal disorders (e.g., pyloric stenosis, achalasia)Obstructive uropathy (e.g., prostatic hyperplasia causing urinary retention)Myasthenia gravis (unless used to reverse anticholinesterase overdose)Tachycardia or unstable cardiovascular status (relative, absolute if severe)
| Precautions | May exacerbate glaucoma (narrow-angle) by inducing mydriasis, Caution in patients with prostatic hyperplasia (risk of urinary retention), Caution in tachyarrhythmias or myocardial ischemia, Heat prostration due to decreased sweating (especially in pediatric or geriatric patients), May cause CNS effects (confusion, delirium) in geriatric patients |
| Food/Dietary |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | Pregnancy Category C. No adequate well-controlled studies in pregnant women. Animal reproductive studies have shown fetal harm (maternal toxicity, fetal loss, growth retardation) at doses 35 times the maximum human dose. Human data limited; no increased risk of major malformations reported. However, atropine may cause fetal tachycardia or decreased fetal heart rate variability; use only if clearly needed with careful fetal monitoring. |
| Fetal Monitoring | Monitor maternal heart rate, blood pressure, and neurologic status; fetal heart rate for tachycardia or decreased variability. In obstetric anesthesia, fetal heart rate monitoring is standard. Monitor for maternal anticholinergic toxicity (dilated pupils, dry skin, altered mental status). |
| Fertility Effects | No human studies on fertility effects. In animal studies, atropine did not impair fertility. Theoretical potential for anticholinergic effects on reproductive function via altered autonomic tone, but clinical significance unknown. |
| No significant food interactions. Avoid excessive alcohol, which may exacerbate CNS depression. |
| Clinical Pearls | Atropine is used in bradycardia at a dose of 0.5 mg IV every 3-5 minutes up to 3 mg total; for organophosphate poisoning, larger doses (2-5 mg IV every 5-10 minutes) are required. Anticholinergic effects (dry mouth, blurred vision) are dose-dependent. Use with caution in glaucoma, prostate hypertrophy, and myasthenia gravis. Atropine can cause paradoxical bradycardia at low doses (<0.5 mg). |
| Patient Advice | Use sunglasses if you experience light sensitivity; avoid driving or operating machinery if vision is blurred. · Dry mouth is common; use sugar-free gum or candy for relief. · Contact your doctor if you experience eye pain, difficulty urinating, or rapid heart rate. · Take exactly as prescribed; do not increase dose without consulting your physician. |