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💊 Pharmacology · Lesson 4 of 6 · 6 min

The Antidote Table You Will See on Exam Day

🧪 Acetaminophen overdose looks harmless for 24 hours and then destroys the liver. The antidote works best in the first 8 hours. The exam gives you a timeline and a drug name and expects an instant match.

💡 Key idea

Naloxone for opioids, flumazenil for benzodiazepines, acetylcysteine for acetaminophen, protamine for heparin, vitamin K for warfarin, calcium gluconate for magnesium.

🧠 Why it matters

OPIOIDS: NALOXONE, which can wear off before the opioid does, so monitor and repeat. BENZODIAZEPINES: FLUMAZENIL, used cautiously because it can trigger seizures in dependent clients. ACETAMINOPHEN: ACETYLCYSTEINE, most effective within 8 hours; liver damage peaks at 72 to 96 hours. HEPARIN: PROTAMINE SULFATE. WARFARIN: VITAMIN K. DIGOXIN: digoxin immune Fab. MAGNESIUM SULFATE (for preeclampsia): CALCIUM GLUCONATE, kept at the bedside; watch for loss of deep tendon reflexes, respirations under 12 and urine output under 30 mL/hr. IRON: deferoxamine. ANTICHOLINERGIC toxicity (hot as a hare, dry as a bone, red as a beet, mad as a hatter): physostigmine. CHOLINERGIC crisis or organophosphates (salivation, lacrimation, urination, defecation, bradycardia): atropine and pralidoxime. BETA-BLOCKER overdose: glucagon. CARBON MONOXIDE: 100% oxygen. METHOTREXATE: leucovorin. LEAD: chelation with succimer or EDTA. CYANIDE: hydroxocobalamin. Dabigatran: idarucizumab. For any suspected poisoning, call the poison control center; do not induce vomiting.

🏥 In the real world

🕗 A teenager arrives six hours after swallowing a bottle of acetaminophen, feeling fine except for mild nausea. Her liver enzymes are normal. The nurse draws a four-hour-plus acetaminophen level and prepares acetylcysteine without waiting for symptoms, because by the time the liver shows damage, the antidote's most protective window has passed.

📌 Takeaways

  • Naloxone may need repeating; flumazenil can cause seizures
  • Acetylcysteine works best within 8 hours of acetaminophen overdose
  • Calcium gluconate at the bedside for every magnesium infusion

📖 Terms in this lesson

Antidote: A drug that reverses the effect of another, such as naloxone for opioids or vitamin K for warfarin.

SLUDGE (cholinergic crisis): Salivation, Lacrimation, Urination, Defecation, GI upset, Emesis: the signs of too much acetylcholine (organophosphate poisoning or cholinergic crisis), reversed with atropine.

Acetaminophen level (toxic): A level above about 150 mcg/mL drawn 4 hours after ingestion is toxic on the Rumack-Matthew nomogram and calls for acetylcysteine; liver enzymes often peak 2 to 4 days later, after the early nausea has settled.

Atropine: The anticholinergic that speeds a symptomatic slow heart (1 mg IV, repeated every 3 to 5 minutes to 3 mg) and the antidote for cholinergic crisis and organophosphate poisoning; expect dry mouth, blurred vision, urinary retention and flushing.

Protamine and vitamin K: The anticoagulant reversal pair: protamine neutralizes heparin within minutes but can cause hypotension and anaphylaxis if pushed fast, while vitamin K (phytonadione) reverses warfarin over hours and is given orally or subcutaneously when possible because IV doses carry a boxed warning for fatal reactions.

Naloxone: The opioid antidote, given IV, IM or intranasally and repeated every 2 to 3 minutes until the client breathes; it wears off before most opioids do, so keep monitoring for returning sedation, and expect sudden pain and withdrawal symptoms.

Acetaminophen: The pain and fever reliever that destroys the liver in overdose while looking harmless for the first day; keep the total under 4 grams daily (less with liver disease or regular alcohol), count combination products, and give acetylcysteine, best within 8 hours.

✅ Test yourself

A client receiving IV magnesium sulfate for preeclampsia has absent patellar reflexes and a respiratory rate of 10. Which medication should the nurse prepare?
  1. Naloxone
  2. Calcium gluconate
  3. Protamine sulfate
  4. Flumazenil

Answer: B · Calcium gluconate

Lost reflexes and respiratory depression are signs of magnesium toxicity; calcium gluconate is the antidote. Stop the infusion first.

Which antidote is administered for acetaminophen overdose?
  1. Acetylcysteine
  2. Deferoxamine
  3. Glucagon
  4. Atropine

Answer: A · Acetylcysteine

Acetylcysteine replenishes glutathione and protects the liver, ideally within 8 hours of ingestion.

After naloxone, a client who overdosed on a long-acting opioid wakes up and breathes normally. Why must the nurse continue close monitoring?
  1. Naloxone wears off before the opioid
  2. Naloxone must be followed by flumazenil
  3. Naloxone causes liver damage
  4. The client will develop serotonin syndrome

Answer: A · Naloxone wears off before the opioid

Naloxone's duration is shorter than many opioids. Resedation and respiratory depression can recur, requiring repeat doses.

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