Atropine
Atropine
Generic Name
Atropine
Mechanism
Atropine is a potent, non‑selective antimuscarinic agent that competitively inhibits acetylcholine binding at muscarinic receptors in the parasympathetic nervous system.
* α‑1‑adrenergic stimulation via muscarinic blockade → peripheral vasoconstriction
* β‑adrenergic blockade through vagal inhibition → increased heart rate
* Disinhibition of the tear ducts, salivary glands, and sweat glands → decreased secretions
* Lipid solubility allows rapid central nervous system penetration at high doses, causing anticholinergic toxicity
Pharmacokinetics
* Absorption – Rapid systemic absorption when given IM, IV, or orally; poor oral bioavailability (~3–5 % during GI intoxication)
* Distribution – Volumes of distribution (34–57 L) reflect high lipophilicity; crosses the blood‑brain barrier and placenta
* Metabolism – Hepatic hydrolysis and conjugation; limited enterohepatic recycling
* Elimination – 30–44 % unchanged in urine; β‑oxidation of the tropane ring; total elimination half‑life 3–6 h (IV), 6–10 h (oral)
Indications
* Bradyarrhythmias – as antidote for digitalis poisoning or vagal overload
* Pre‑operative parasympatholysis – reduces salivary, bronchial, and gastric secretions
* Ophthalmic – pupil dilation (mydriasis) for eye exams
* Bee/wasp stings – epinephrine‑enhanced first‑line treatment
* Poison control – as a broad‑spectrum anticholinergic antidote
Contraindications
* Severe hepatic or renal dysfunction – may prolong anticholinergic effects
* Ocular glaucoma or angle‑closure – mydriasis can worsen intra‑ocular pressure
* Neuromuscular disease (myasthenia gravis) – can precipitate respiratory failure
* Undiagnosed narrow‑angle glaucoma – contraindicated
* Allergy to atropine or structurally related alkaloids – avoid
* Caution in elderly or children – heightened susceptibility to CNS toxicity
Dosing
| Setting | Dose | Route | Frequency | Notes |
| Adult | 0.5 mg IV | IV/IM | Every 3–5 min until HR > 70 bpm or MAP normalized | Maximum cumulative dose 3 mg |
| Pediatric | 0.1–0.2 mg/kg IV (max 2 mg) | IV/IM | Repeat every 5 min up to 4 mg total | Monitor respiratory function |
| Ophthalmology | 1 % ophthalmic solution (0.05 mg each eye) | Topical | Once for dilation | 5–10 min to achieve mydriasis |
| Adverse Effects | 0.02 mg/kg PO | Oral | Once daily | For chronic secretory disorders |
| Bees/wasp stings | 1–3 mg IM | IM | Single shot | Use alongside epinephrine and antihistamine |
*Always titrate to effect and monitor vitals.*
Adverse Effects
| Category | Examples |
| Common | Dry mouth, blurred vision, flushing, tachycardia, urinary retention |
| Neurologic | Dizziness, anxiety, hallucinations at high doses |
| Respiratory | Dry cough, hypersalivation ↓ (rarely ↑), airway edema in severe overdose |
| Serious | Seizures, status epilepticus, arrhythmia (ST‑segment changes), anaphylaxis (rare) |
*Adverse events are dose‑dependent and may correlate with plasma concentration.*
Monitoring
* Heart rate and rhythm – continuous ECG for bradyarrhythmia patients
* Blood pressure – MAP ≥ 65 mmHg requirement
* Pupil size – monitor for excessive mydriasis or angle‑closure risk
* Respiratory status – signs of ventilation impairment, especially in myasthenia gravis patients
* Serum electrolytes – potassium, magnesium for arrhythmia risk
* Symptom diary – record CNS symptoms in outpatient dosing
Clinical Pearls
1. “Digitalis Storm” Neccs – The standard antidote for digitalis overdose: 0.5 mg IV atropine until the heart rate rises > 70 bpm and MAP ≥ 80 mmHg; *limit cumulative to 3 mg* to avoid atropine toxicity.
2. “Parenteral Rapid Start” – In pediatric cardiac arrest, start at 0.1 mg/kg IV; use a crisp 0.5 mg IV line where weight unknown; rapid titration reduces bradycardia risk.
3. “Eye‑Care Nuance” – For mydriasis, *avoid* mydriatic combinations (e.g., phenylephrine) in patients with fragile ocular tissue—use atropine alone.
4. “Off‑Label Not‑to‑Exceed” – Chronic dosing for over‑exposure to cholinergic toxins or hypersecretory states shouldn’t exceed 0.02 mg/kg PO daily; long‑term exposure may precipitate cognitive impairment.
5. “Centrally Acting Toxicity” – In overdose, 3 mg may reverse mental status; use pyridostigmine or pralidoxime for organophosphate poisoning rather than atropine alone to reduce mortality.
6. “Glaucoma Guests” – A history of narrow‑angle glaucoma, even if untreated, contraindicates atropine use; consider cycloplegic agents like cyclopentolate instead.
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