Atropine

ATROPEN

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Pronunciation: A-troe-peen (at-ROE-pen)

Atropine ballicule: receptor binding, kinetics and half-life diagram — Mechanism of action: Atropine ballicule

Atropine ATROPEN mascot mnemonic cartoon — Visual mnemonic: Atropine mascot
**“AT-AT pen”**
“Mad as a hatter” → BBB-crossing antimuscarinic
“red as a beet” → anticholinergic

What it isAntimuscarinic; symptomatic bradycardia, organophosphate poisoning and secretion control.

Why this oneReverses vagally mediated bradycardia within a minute, and in organophosphate poisoning it is titrated to drying of secretions with no ceiling dose.

What limits itCrosses into the CNS, causing delirium in the elderly. Ineffective in infranodal block and in transplanted hearts.

Atropine molecular structure (skeletal formula) — Molecular structure: Atropine

FDA-approved for

bradycardia/organophosphate poisoning (~1960)

Off-label

clozapine-induced sialorrhea (sublingual drops)

Principal riskDelirium in the elderly from CNS penetration

Classes and tags

Clinical profile

Therapeutic safety burden2 / 4

Overdose danger1 / 4

Weight-gain liability0 / 4

Sedation liability0 / 4

QT / Torsades0 / 4

Direct muscarinic antagonism4 / 4

Embryofetal risk1 / 4

Legacy pregnancy categoryC

Defining liabilityGenerally tolerated at therapeutic doses; clinically important risks are agent-specific and increase with interactions or organ impairment.

FDA label

Read the full label on DailyMed ↗

NO BOXED WARNINGS

FDA dosing	Population	Start	Target	Max
Organophosphorus nerve agent or organophosphorus/carbamate insecticide poisoning	Adults & peds >41 kg (generally >10 y)	Mild (two or more mild symptoms): one 2 mg (green) injection IM once	If severe symptoms develop after 1st dose: two more injections in rapid succession. Severe or unconscious at outset: three injections in rapid succession	3 injections (2 mg each) in labeled regimen
Organophosphorus nerve agent or organophosphorus/carbamate insecticide poisoning	Peds 18–41 kg (generally 4–10 y)	Mild (two or more mild symptoms): one 1 mg (red) injection IM once	If severe symptoms develop after 1st dose: two more injections in rapid succession. Severe or unconscious at outset: three injections in rapid succession	3 injections (1 mg each) in labeled regimen
Organophosphorus nerve agent or organophosphorus/carbamate insecticide poisoning	Peds 7–18 kg (generally 6 mo–4 y)	Mild (two or more mild symptoms): one 0.5 mg (blue) injection IM once	If severe symptoms develop after 1st dose: two more injections in rapid succession. Severe or unconscious at outset: three injections in rapid succession	3 injections (0.5 mg each) in labeled regimen
Organophosphorus nerve agent or organophosphorus/carbamate insecticide poisoning	Peds <7 kg (generally <6 mo)	Mild (two or more mild symptoms): one 0.25 mg (yellow) injection IM once	If severe symptoms develop after 1st dose: two more injections in rapid succession. Severe or unconscious at outset: three injections in rapid succession	3 injections (0.25 mg each) in labeled regimen

Titration Wait 10–15 min after first injection; if no severe symptoms develop, no additional injections

Renal Undefined (PK not evaluated in renal impairment)

Hepatic Undefined (PK not evaluated in hepatic impairment)

Initial treatment of muscarinic symptoms only. Severe poisoning: consider concurrent benzodiazepine if seizure suspected; pralidoxime may be an adjunct. Geriatric: longer half-life, may need less frequent doses after the initial dose

Instructions

IM into mid-lateral (outer) thigh at 90°, through clothing OK (empty pockets); hold firmly at least 10 seconds, then massage site
Very thin people and small children: bunch up the thigh before injecting
Give as soon as symptoms appear, only when exposure is known or suspected; keep three autoinjectors available per at-risk patient
Second and third injections preferably given by someone other than the patient
After use: bend needle back, pin used autoinjectors to patient's clothing or show to medical personnel
Inspect for particulate matter and discoloration when container permits
Close supervision for at least 48 to 72 hours; seek definitive medical care immediately

Available strengths

inj 0.25, 0.5, 1 mg
drops 1 %
sol 8 mg/20 mL
ointment 10 mg/g

Cautions

Cardiovascular risks (tachyarrhythmias; caution in CV disease or conduction problems)
Heat injury — may inhibit sweating; avoid excessive exercise and heat
Acute glaucoma in susceptible patients
Urinary retention with bladder outflow obstruction
Pyloric stenosis — may cause complete obstruction
Exacerbation of chronic lung disease (viscid bronchial plugs)
Hypersensitivity incl. anaphylaxis

Adverse reactions

Dry mouth
Blurred vision
Dry eyes
Photophobia
Confusion
Headache
Dizziness
Tachycardia, palpitations
Flushing
Urinary hesitancy or retention
Constipation, abdominal pain/distention
Nausea, vomiting

Pregnancy Crosses the placenta; no adequate human data and no adequate animal reproduction studies

Lactation Reported excreted in human milk; no data on breastfed infant or milk production — weigh benefits vs maternal need

Cost

Atropine (ATROPEN)

Strength		#/mo	CostPlus
0.25 mg	inj	per unit	not offered
0.5 mg	inj	per unit	not offered
1 mg	inj	per unit	not offered

NADAC is a voluntary CMS survey of what retail community pharmacies pay for the drugs they stock. Atropine is administered under clinical supervision and dispensed outside retail pharmacies, so it rarely appears on surveyed invoices.

Other forms: Atropine eyedrops (ISOPTO ATROPINE)

Available combined with: Difenoxin (in MOTOFEN) · Diphenoxylate (in LOMOTIL) · diphenoxylate / atropine

Generic entry2020

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Memory aids: interaction avatars

Box: minimal PK interactions

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Self-check

What is atropine titrated to in organophosphate poisoning?
Drying secretions, with no ceiling dose.
In which two cardiac settings is atropine ineffective?
Infranodal block and transplanted hearts.