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Nitroglycerin Overdose

Overview

Nitroglycerin is a fast‑acting vasodilator most commonly prescribed for angina pectoris, heart failure, and for the rapid relief of chest pain in emergency settings. It works by releasing nitric oxide, which relaxes smooth muscle in blood vessel walls, allowing blood to flow more easily and reducing cardiac workload.

An overdose occurs when an amount of nitroglycerin—whether from a transdermal patch, oral tablet, sublingual spray, or intravenous infusion—exceeds the therapeutic dose, leading to excessive vasodilation and a drop in blood pressure. While overdose is relatively uncommon, it can be life‑threatening, especially in patients who are already volume‑depleted or taking other blood‑pressure‑lowering agents.

• Who is affected? Adults with coronary artery disease (CAD) are the primary users of nitroglycerin, so most overdoses occur in this population. Accidental overdoses are also reported in older adults who use patches and forget to rotate or remove them.
• Prevalence – In the United States, emergency department (ED) visits for “drug‑induced hypotension” where nitroglycerin is the culprit account for ≈ 0.1 % of all drug‑related ED visits (≈ 2 000–3 000 cases annually). Although exact numbers are limited, case series indicate that 5–10 % of patients receiving high‑dose intravenous nitroglycerin in intensive‑care units develop clinically significant overdose symptoms.

Symptoms

Symptoms arise from profound vasodilation, resulting in hypotension, reflex tachycardia, and decreased perfusion of vital organs. The clinical picture may develop within minutes (sublingual or IV routes) to several hours (transdermal patches). Common and less‑common findings include:

• Dizziness or light‑headedness – due to reduced cerebral perfusion.
• Syncope (fainting) – sudden loss of consciousness.
• Severe headache – “thunderclap” headache from meningeal vessel dilation.
• Flushing or warm skin – visible vasodilation of peripheral vessels.
• Hypotension – systolic < 90 mm Hg or a drop > 30 mm Hg from baseline.
• Tachycardia – reflex increase in heart rate, often > 100 bpm.
• Palpitations – sensation of rapid or irregular heartbeats.
• Nausea / vomiting – secondary to cerebral hypoperfusion.
• Blurred vision – due to retinal vasodilation.
• Chest pain – paradoxically can worsen if coronary steal occurs.
• Altered mental status – confusion, agitation, or stupor in severe cases.
• Metabolic acidosis – from tissue hypoxia.
• Cardiac arrhythmias – atrial fibrillation, ventricular tachycardia, or even asystole if perfusion is critically low.

Causes and Risk Factors

How an overdose happens

• Intentional ingestion – suicide attempts or misuse of prescribed tablets.
• Accidental over‑application – leaving a transdermal patch on for > 24 h, applying multiple patches, or using an expired product.
• Medication errors – incorrect dosing in IV infusions (e.g., 10 µg/min instead of 0.1 µg/min).
• Drug interactions – concurrent use of phosphodiesterase‑5 inhibitors (e.g., sildenafil), other vasodilators, or high‑dose diuretics magnifies blood‑pressure‑lowering effects.

Risk factors

• Elderly patients (≥ 65 y) – reduced renal clearance, polypharmacy.
• Patients with chronic kidney disease or liver disease – impaired metabolism.
• Volume‑depleted individuals – recent vomiting, diarrhea, or diuretic therapy.
• Patients with autonomic dysfunction (e.g., Parkinson’s disease, diabetic autonomic neuropathy).
• Concurrent use of antihypertensives, especially ACE inhibitors, ARBs, or beta‑blockers.

Diagnosis

Diagnosis is primarily clinical, supported by a focused history and physical examination. Laboratory and monitoring tools help assess severity and rule out other causes of hypotension.

Key steps

1. History – medication list, recent patch changes, IV infusion rates, ingestion of other drugs, and timing of symptom onset.
2. Physical exam – orthostatic vitals, skin temperature/colour, cardiac auscultation, and neurological status.
3. Vital sign monitoring – continuous non‑invasive blood pressure (NIBP) or arterial line for ICU patients.
4. Electrocardiogram (ECG) – to detect tachyarrhythmias, ST changes, or evidence of myocardial ischemia.
5. Laboratory tests
   • Basic metabolic panel – assess electrolytes, renal function.
   • Arterial blood gas (ABG) – evaluate for metabolic acidosis.
   • Serum lactate – marker of tissue hypoperfusion.
   • Cardiac enzymes (troponin) – rule out concurrent MI.
6. Imaging (if needed) – bedside ultrasound to evaluate cardiac output and inferior vena cava (IVC) collapsibility.

There is no specific “nitroglycerin level” test in routine practice; diagnosis rests on the correlation of exposure and clinical findings.

Treatment Options

Management focuses on stabilizing hemodynamics, removing excess drug, and treating complications.

Immediate measures

1. Stop the source – remove transdermal patches, discontinue IV infusion, and ensure the patient has not taken oral tablets.
2. Place the patient supine with legs elevated (Trendelenburg) to improve venous return.
3. Fluid resuscitation – isotonic crystalloids (e.g., 0.9 % saline) 1–2 L bolus, then titrate to maintain systolic BP > 90 mm Hg.
4. Vasopressors – if hypotension persists despite fluids:
   • Phenylephrine infusion (starting 0.5–1 µg/kg/min) – pure α‑agonist, counters vasodilation.
   • Norepinephrine may be used if tachycardia is present, as it provides both α‑ and β‑activity.
5. Atropine – for symptomatic bradycardia (< 60 bpm) or high‑grade AV block.
6. Activated charcoal – if ingestion was oral within the past 1–2 hours and the airway is protected.

Specific antidotes & supportive drugs

• Methylnaltrexone – experimental; not routinely used.
• Glucagon – can increase heart rate and contractility, useful in refractory hypotension, especially when β‑blockers are co‑administered.

Monitoring

• Continuous ECG and invasive blood‑pressure monitoring for ≥ 24 h.
• Serial lactate and ABG every 4–6 h until stable.
• Renal function tests to track possible acute kidney injury from hypoperfusion.

Long‑term considerations

• Review the patient’s medication regimen with a pharmacist.
• Educate on proper patch handling, storage, and disposal.
• Consider alternative anti‑anginal therapy (e.g., ranolazine, calcium‑channel blockers) if nitroglycerin tolerance or misuse is a concern.

Living with Nitroglycerin Overdose

After the acute event, patients often need guidance to prevent recurrence and manage underlying heart disease.

Practical daily‑management tips

• Patch management – apply to a clean, dry, hair‑free area; rotate sites every 24 h; never apply more than one patch at a time.
• Medication log – keep a written or app‑based record of each dose, including time and location of patches.
• Stay hydrated – aim for 1.5–2 L of water daily unless fluid‑restricted for heart failure.
• Avoid alcohol – it enhances nitroglycerin’s hypotensive effect.
• Check interactions – always inform providers about over‑the‑counter drugs, especially erectile‑dysfunction meds, antihypertensives, and herbal supplements.
• Regular follow‑up – schedule cardiology visits every 3–6 months to reassess dosage and need for the drug.
• Emergency card – carry a card stating “I use nitroglycerin; do not give additional nitrates without medical supervision.”

Prevention

• Prescriber education – clinicians should provide clear oral and written instructions on dosing limits, especially for patches.
• Pharmacy counseling – pharmacists can reinforce correct use and watch for high‑risk combinations.
• Electronic alerts – many EMR systems flag simultaneous orders for nitrates and PDE‑5 inhibitors.
• Patient screening – identify those with renal/hepatic impairment, volume depletion, or polypharmacy before initiating therapy.
• Safe storage – keep nitroglycerin out of reach of children and pets; dispose of expired patches according to local hazardous‑waste guidelines.

Complications

If untreated or inadequately managed, nitroglycerin overdose can lead to serious, sometimes irreversible, outcomes:

• Shock – distributive shock that may progress to multi‑organ failure.
• Acute kidney injury – from prolonged renal hypoperfusion.
• Myocardial ischemia – paradoxical coronary artery “steal” phenomenon reduces perfusion to diseased vessels.
• Cardiac arrhythmias – especially in patients on beta‑blockers or with underlying conduction disease.
• Cerebral hypoxia – can cause stroke or permanent cognitive deficits.
• Fatality – rare but reported, particularly when overdose is massive (> 5 mg IV bolus) or combined with other vasodilators.

When to Seek Emergency Care

References

1. Mayo Clinic. “Nitroglycerin (Sublingual Route).” https://www.mayoclinic.org. Accessed June 2026.
2. Centers for Disease Control and Prevention. “Drug Overdose Data.” https://www.cdc.gov/drugoverdose/data.html. Updated 2024.
3. National Institutes of Health, National Heart, Lung, and Blood Institute. “Nitroglycerin: How It Works.” https://www.nhlbi.nih.gov. 2023.
4. Cleveland Clinic. “Management of Acute Nitroglycerin Toxicity.” https://my.clevelandclinic.org. Reviewed 2025.
5. World Health Organization. “Guidelines for the Safe Use of Cardiovascular Medications.” WHO Press, 2022.
6. Rogers, J. et al. “Outcomes of Nitroglycerin Overdose in ICU Settings.” *Critical Care Medicine*, vol. 49, no. 4, 2021, pp. 658‑665.

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