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Antidotes cheat sheet: common drugs and their antidotes

Antidote questions come down to two things: match the drug to its reversal agent, then know what improvement looks like.

This sheet pairs each drug with its antidote and the sign that the antidote is working.

Built from NurseLingo's RN-written study decks· Updated Oct 2026· Sources

Toxin/DrugAntidoteProof It Worked
DigoxinDigoxin immune Fab (DigiFab)
  • Rhythm stabilizes; recheck K+
  • Nausea, halos resolve
HeparinProtamine sulfate
  • aPTT trends toward normal
  • Give slowly: hypotension, anaphylaxis
WarfarinVitamin K (phytonadione)
  • INR drifts back to 2-3
  • Major bleed: IV vit K + 4F-PCC
OpioidsNaloxone (Narcan)
  • RR improves, client wakes
  • May need re-dosing
BenzodiazepinesFlumazenil
  • Alertness returns
  • Seizure risk on reversal
AcetaminophenN-acetylcysteine (NAC)
  • Best within 8 hr of ingestion
  • Liver enzymes stay normal
Magnesium sulfateCalcium gluconate
  • Stop the Mg drip
  • RR back above 12
Iron (overdose)Deferoxamine
  • Chelates iron
  • Used in acute overdose

RN pearl: If the antidote worked, the target sign or lab normalizes: pulse, INR, RR, or reflexes.

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Frequently asked questions

What is the antidote for heparin?

Protamine sulfate. The aPTT should trend back toward normal.

What is the antidote for warfarin?

Vitamin K (phytonadione). The INR should drift back toward the goal range. For major bleeding, IV vitamin K is given with 4-factor prothrombin complex concentrate (4F-PCC).

What is the antidote for an opioid overdose?

Naloxone (Narcan). Watch the respiratory rate and level of consciousness. Naloxone can wear off before the opioid does, so the client may need another dose.

What is the antidote for magnesium sulfate toxicity?

Calcium gluconate, and stop the magnesium infusion. The respiratory rate should rise back above 12.

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Sources

  1. Pharmacology for Nurses, 20.2 Anticoagulants, OpenStax
  2. Pharmacology for Nurses, 14.3 Opioid Agonists and Antagonists, OpenStax
  3. Acetaminophen Toxicity, StatPearls, NCBI Bookshelf
  4. Protamine Sulfate Injection: prescribing information, DailyMed, U.S. National Library of Medicine

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