ATROPINE (AUTOINJECTOR)
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ATROPINE (AUTOINJECTOR) (ATROPINE (AUTOINJECTOR)).
Competitive antagonist of muscarinic acetylcholine receptors (M1, M2, M3, M4, M5), blocking the effects of acetylcholine and other cholinergic agonists.
| Metabolism | Hepatic metabolism via glucuronidation and hydrolysis; minor metabolism by cytochrome P450 enzymes (CYP3A4, CYP2D6). |
| Excretion | Renal: ~30-50% unchanged; hepatic metabolism: ~50%; fecal: minor. |
| Half-life | Terminal elimination half-life: 2-4 hours (adults); prolonged to 6-12 hours in elderly or hepatic impairment. |
| Protein binding | 14-22% bound to albumin. |
| Volume of Distribution | 2-4 L/kg, indicating extensive tissue distribution. |
| Bioavailability | IM: ~90% (rapid and complete absorption). |
| Onset of Action | IM: 1-2 minutes; IV: 30 seconds to 1 minute. |
| Duration of Action | IM/IV: 2-6 hours (clinical effects on heart rate, secretions); up to 8-12 hours at higher doses. |
2 to 4 mg intramuscularly (lateral thigh) or intravenously, repeated every 10-20 minutes if needed until muscarinic signs abate, maximum 3 doses.
| Dosage form | SOLUTION |
| Renal impairment | No dose adjustment required for renal impairment; eliminated primarily by hepatic metabolism. |
| Liver impairment | No specific Child-Pugh based guidelines available; use with caution in severe hepatic impairment due to potential increased bioavailability. |
| Pediatric use | Weight-based: 0.05 mg/kg intramuscularly (max 2 mg) or intravenously, repeat every 10-20 minutes as needed. |
| Geriatric use | Start at lower end of adult dose (e.g., 2 mg); monitor for CNS effects (confusion, delirium) and anticholinergic side effects (urinary retention, constipation). |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ATROPINE (AUTOINJECTOR) (ATROPINE (AUTOINJECTOR)).
| Breastfeeding | Atropine is excreted into breast milk in small amounts; estimated infant dose <0.02% of maternal weight-adjusted dose. M/P ratio unknown. No adverse effects reported in infants. Use with caution due to potential anticholinergic effects in neonates. |
| Teratogenic Risk | Pregnancy Category C. Atropine crosses the placenta. First trimester: No well-controlled studies; animal studies show no teratogenicity at therapeutic doses but embryotoxicity at high doses. Second/third trimester: May cause fetal tachycardia and decreased variability on fetal heart rate monitoring. Near term: Respiratory depression or neonatal meconium plug syndrome has not been reported but theoretical risk exists. |
■ FDA Black Box Warning
Not indicated for use in severe poisoning (e.g., organophosphate toxicity) without adequate doses; may cause paradoxical bradycardia at low doses. Use in such emergencies requires immediate medical attention.
| Serious Effects |
["Hypersensitivity to atropine or any component of the formulation","Angle-closure glaucoma","Obstructive gastrointestinal disease (e.g., pyloric stenosis, ileus)","Obstructive uropathy (e.g., bladder neck obstruction due to prostatic hypertrophy)","Myasthenia gravis (unless used to counteract anticholinesterase side effects)","Tachycardia or acute myocardial infarction with tachycardia","Severe hepatic impairment"]
| Precautions | ["Tachycardia and palpitations; avoid in patients with tachyarrhythmias.","Exacerbation of glaucoma; monitor intraocular pressure.","Urinary retention; use with caution in patients with prostatic hyperplasia.","Central nervous system effects (e.g., confusion, hallucinations) particularly in elderly.","Hyperthermia due to decreased sweating; avoid in hot environments.","Not for self-treatment; auto-injectors are for emergency use only."] |
| Food/Dietary |
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| Fetal Monitoring | Monitor maternal heart rate, blood pressure, and signs of anticholinergic toxicity. For fetal monitoring, assess fetal heart rate and variability due to potential tachycardia and decreased variability. No specific fetal monitoring required beyond standard prenatal care. |
| Fertility Effects | Atropine may inhibit salivary, bronchial, and sweat gland secretions; no direct effects on fertility reported. Anticholinergic effects can cause vaginal dryness and urinary retention but fertility impairment is not documented. |
| No known food interactions. Maintain hydration to counteract anticholinergic effects like dry mouth. |
| Clinical Pearls | Atropine autoinjector is indicated for acute nerve agent or organophosphate poisoning. Administer via intramuscular injection into the mid-outer thigh (vastus lateralis) through clothing if necessary. Can be repeated every 5-10 minutes if severe symptoms persist. Anticholinergic effects include mydriasis, dry mouth, tachycardia, and urinary retention. Contraindicated in narrow-angle glaucoma and obstructive GI disorders except in life-threatening poisoning. Monitor for paradoxical bradycardia at low doses. |
| Patient Advice | Use only in emergency situations involving nerve agent or organophosphate poisoning. · Inject into the outer thigh, not the buttock or arm. · Hold autoinjector in place for 10 seconds after activation. · Seek immediate medical attention after use. · Report any side effects such as blurred vision, dry mouth, or rapid heartbeat. |