ATROPEN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ATROPEN (ATROPEN).
Competitive antagonist of muscarinic acetylcholine receptors (M1, M2, M3, M4, M5). Blocks parasympathetic nerve impulses, leading to increased heart rate, bronchodilation, decreased secretions, and mydriasis.
| Metabolism | Hepatic via enzymatic hydrolysis. Approximately 50% metabolized to tropine and tropic acid. CYP450 involvement is minimal. |
| Excretion | Renal: ~50% unchanged; hepatic metabolism (hydrolysis) accounts for ~30-40%; fecal: <5%. |
| Half-life | Terminal half-life ~2-3 hours in adults; prolonged in elderly and infants due to reduced clearance. |
| Protein binding | ~44% primarily to albumin. |
| Volume of Distribution | ~2-4 L/kg; extensive tissue distribution with significant CNS penetration. |
| Bioavailability | IM: ~75%; Oral: ~10-25% (high first-pass metabolism); Inhalation: variable (10-30% systemic). |
| Onset of Action | IV: <1 minute; IM: 2-5 minutes; Oral: 30-60 minutes; Inhalation: 15-30 minutes. |
| Duration of Action | IV/IM: 1-2 hours (vagal blockade); Oral: 4-6 hours; Ophthalmic: up to 7-14 days for mydriasis/cycloplegia. |
0.5 to 1 mg IV/IM/SC every 3 to 5 minutes as needed; maximum 3 mg total. For bradycardia: 0.5 mg IV every 3-5 minutes to a maximum of 3 mg. For organophosphate poisoning: 2 mg IV/IM initially, then 2 mg every 5-10 minutes until atropinization.
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for renal impairment; pharmacokinetics unchanged. |
| Liver impairment | No specific guidelines; use with caution in severe hepatic impairment due to potential altered metabolism. |
| Pediatric use | Bradycardia: 0.02 mg/kg IV/IO/ET (minimum 0.1 mg, maximum 1 mg) repeated every 5 minutes to a maximum total of 1 mg in children, 2 mg in adolescents. Organophosphate poisoning: 0.05 mg/kg IV/IM (minimum 0.1 mg) every 5-10 minutes as needed. |
| Geriatric use | Lower initial doses recommended (0.5 mg IV) due to increased sensitivity and risk of anticholinergic effects; titrate slowly; maximum 3 mg total unless for poisoning. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ATROPEN (ATROPEN).
| Breastfeeding | Atropine is excreted in breast milk in small amounts. M/P ratio is approximately 1.1. Risk to nursing infant is low at therapeutic doses, but caution is advised due to potential anticholinergic effects. Monitor infant for gastrointestinal disturbances and tachycardia. |
| Teratogenic Risk | FDA Pregnancy Category C. Atropine crosses the placenta. First trimester: limited data, but animal studies show no teratogenicity at clinically relevant doses. Second and third trimesters: fetal tachycardia and decreased variability on fetal heart rate monitoring may occur; avoid prolonged high doses. No known teratogenic effects. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Known hypersensitivity to atropine or any component","Narrow-angle glaucoma (unless prescribed by an ophthalmologist)","Acute hemorrhage with unstable cardiovascular status","Obstructive gastrointestinal disease such as pyloric stenosis","Myasthenia gravis (except when used to reverse anticholinesterase agents)"]
| Precautions | ["Use with caution in patients with coronary artery disease, cardiac arrhythmias, hyperthyroidism, or congestive heart failure.","May exacerbate glaucoma, pyloric stenosis, or prostatic hypertrophy.","May cause heat stroke due to suppression of sweating.","Use with caution in patients with Down syndrome due to increased sensitivity to anticholinergic effects."] |
| Food/Dietary | No significant food interactions. Decreased absorption with high-fat meals; take on an empty stomach if possible. |
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| Fetal Monitoring | Monitor maternal heart rate, blood pressure, and gastrointestinal status. In pregnancy, fetal heart rate should be monitored for tachycardia and decreased variability during prolonged use. Assess for anticholinergic side effects including dry mouth, blurred vision, and urinary retention. |
| Fertility Effects | Atropine does not significantly impair fertility. No known direct effects on spermatogenesis or oogenesis. However, caution in use during early pregnancy due to potential fetal effects. |
| Clinical Pearls | For bradycardia, administer 0.5 mg IV push every 3-5 minutes up to 3 mg total. For organophosphate poisoning, give 2-5 mg IV/IM every 5-10 minutes until muscarinic signs resolve. Use with caution in glaucoma, prostatic hypertrophy, and myasthenia gravis. Monitor for tachyarrhythmias. May cause blurred vision and photophobia. |
| Patient Advice | This medication may cause dry mouth, blurred vision, and sensitivity to light. · Avoid driving or operating machinery until effects diminish. · Notify your doctor if you have a history of glaucoma or difficulty urinating. · If using for poisoning, report any new symptoms like muscle twitching or excessive secretions. |