Situation: A 45-year-old farmer weighing 60 kg is brought to the emergency department 1 hour after drinking an organophosphate insecticide. He has pinpoint pupils, profuse salivation, wheezing with crackles in both lungs, and a heart rate of 48/min. His clothing has been removed and his skin washed. Atropine is given by the doubling protocol, followed by a continuous infusion. The first atropine dose was 2 mg intravenously, and each later dose was double the one before, given every 5 minutes. The target end points were reached with the fourth dose. The maintenance order is 10% of the total loading dose per hour. What hourly dose should the nurse program?

The four doses are 2, 4, 8, and 16 mg, for a total loading dose of 30 mg. Ten percent of 30 mg is 3 mg/hour. The infusion is then titrated to keep the chest clear without causing atropine toxicity.

Clinical context
Organophosphate (OP) insecticides irreversibly inhibit acetylcholinesterase, allowing acetylcholine to accumulate at muscarinic, nicotinic, and central synapses. The classic muscarinic picture includes pinpoint pupils, bronchorrhea with wheezing and crackles, salivation, bradycardia, and diaphoresis. Atropine is a competitive muscarinic antagonist, so it does not reverse the enzyme inhibition itself; it blocks acetylcholine at muscarinic receptors, especially in the lungs, heart, and glands. The immediate priority in the emergency department is airway and breathing support because bronchorrhea and bronchospasm can cause rapid respiratory failure.

Dose calculation
The doubling protocol starts with 2 mg intravenously. Each subsequent dose is double the previous dose and is given every 5 minutes until the target end points are reached.

Dose number	Atropine dose
First	2 mg
Second	4 mg
Third	8 mg
Fourth	16 mg
Total loading dose	30 mg

The maintenance infusion is ordered as 10% of the total loading dose per hour. Ten percent of 30 mg is 3 mg/hour. Therefore, the nurse should program 3 mg/hour.

Why the doubling protocol is used
The doubling-dose strategy rapidly escalates atropine until muscarinic signs are controlled, then converts to a titrated maintenance infusion. In severe OP poisoning, patients may require very large total doses of atropine because acetylcholine continues to accumulate at muscarinic receptors. A fixed low-dose regimen often fails to clear the chest or reverse bradycardia. The doubling approach provides a structured, reproducible method for reaching the clinical end points: clear breath sounds, heart rate above 80/min, dry secretions, and systolic blood pressure above 80 mm Hg.

Titration after the loading phase
Once the target end points are achieved, the infusion is not left at a fixed rate indefinitely. The maintenance dose is titrated to keep the chest clear while avoiding atropine toxicity. Signs of atropine toxicity include confusion, hallucinations, hyperthermia, dry flushed skin, urinary retention, and ileus. The nurse must monitor lung sounds, secretions, pupil size, heart rate, temperature, and mental status at frequent intervals. If bronchial secretions return or wheezing worsens, the infusion may need to be increased. If the patient develops agitation, fever, or absent bowel sounds, the infusion should be reduced or paused.

Clinical monitoring priorities
The patient’s initial presentation includes bradycardia at 48/min, which reflects muscarinic stimulation of the sinoatrial node. Atropine should increase the heart rate as muscarinic blockade takes effect. However, Watch out! Severe OP poisoning can also cause nicotinic effects such as muscle fasciculations and weakness, which atropine does not reverse. Respiratory muscle weakness and central respiratory depression may still require ventilatory support even when atropine has dried the secretions. Oximes such as pralidoxime are used to reactivate acetylcholinesterase, but atropine remains the first-line agent for acute muscarinic crisis.

Common calculation errors
A frequent mistake is to use only the last dose, 16 mg, instead of the total loading dose. Ten percent of 16 mg would be 1.6 mg/hour, which is incorrect because the maintenance rate is based on the cumulative amount given during loading. Another error is to average the doses or to stop doubling after the third dose. Key point! The total loading dose is the sum of all doses administered until the target end points are reached, not the final dose alone.

Evidence context
The doubling-dose approach has been compared with unstructured or ad hoc atropine regimens in observational studies of OP and carbamate poisoning ^[1]. A randomized trial in Bangladesh also examined bolus-only atropine versus incremental boluses plus infusion, reflecting ongoing uncertainty about the optimal maintenance strategy ^[2]. In resource-limited settings without intensive care, protocols using atropine without intubation have been described, emphasizing the importance of structured dosing and close clinical monitoring ^[3]. An umbrella review of systematic reviews has summarized the broader therapeutic evidence for OP poisoning, including atropine and oxime use ^[4]. These sources support the principle that atropine dosing must be individualized and titrated to clinical response, with the maintenance infusion derived from the total loading dose.