Antidotes and Drug Levels
Reversal agents and therapeutic ranges you're expected to know
Antidotes and reversal agents
| Drug or poison | Antidote |
|---|---|
| Opioids | Naloxone (may need repeat doses: it wears off before many opioids) |
| Benzodiazepines | Flumazenil (can trigger seizures in long-term users) |
| Acetaminophen | Acetylcysteine (best within 8 h) |
| Heparin | Protamine sulfate (partial for enoxaparin) |
| Warfarin | Vitamin K; 4-factor PCC for serious bleeding |
| Dabigatran | Idarucizumab |
| Apixaban, rivaroxaban | 4-factor PCC (andexanet alfa was withdrawn from the US market in Dec 2025) |
| Digoxin | Digoxin immune fab |
| Beta blockers | Glucagon (also calcium, high-dose insulin) |
| Calcium channel blockers | Calcium, high-dose insulin, glucagon |
| Insulin, sulfonylureas | Glucose / glucagon; octreotide for sulfonylureas |
| Magnesium sulfate | Calcium gluconate |
| Drug or poison | Antidote |
|---|---|
| Anticholinergics | Physostigmine |
| Organophosphates, cholinergic crisis | Atropine + pralidoxime |
| Tricyclic antidepressants | Sodium bicarbonate (wide QRS) |
| Aspirin (salicylates) | Sodium bicarbonate; dialysis if severe |
| Iron | Deferoxamine |
| Lead | Succimer, edetate calcium disodium, dimercaprol |
| Cyanide (incl. nitroprusside) | Hydroxocobalamin |
| Methanol, ethylene glycol | Fomepizole |
| Methotrexate | Leucovorin |
| Isoniazid overdose | Pyridoxine (vitamin B6) |
| Local anesthetic toxicity | Lipid emulsion 20% |
| Malignant hyperthermia | Dantrolene |
| Serotonin syndrome | Cyproheptadine + supportive care |
Therapeutic drug levels
| Digoxin | 0.5–2.0 ng/mL (0.5–0.9 target in HF) |
| Lithium | 0.6–1.2 mEq/L; toxic >1.5 |
| Phenytoin | 10–20 mcg/mL |
| Valproic acid | 50–100 mcg/mL |
| Carbamazepine | 4–12 mcg/mL |
| Theophylline | 10–20 mcg/mL (many now aim 5–15) |
| Vancomycin | AUC 400–600 (trough-based dosing in some settings) |
| Gentamicin | Depends on regimen; low trough (<1–2 mcg/mL) |
Coagulation targets
| Heparin | aPTT ~1.5–2.5 × control, or anti-Xa 0.3–0.7 (per protocol) |
| Warfarin | INR 2–3; 2.5–3.5 for some mechanical valves (e.g., mitral) |
| Normal INR | ~0.8–1.1 (not on warfarin) |
Timing
- Trough: just before the next dose (lowest level).
- Peak: at a set time after the dose (e.g., 30 min after an IV infusion ends).
- High trough = toxicity risk; low peak = not effective.
Memory hook
"Protamine for the Hep (you need a pro to stop heparin)" · "K kills warfarin's effect" · "Glucagon for beta blockers and insulin" · "Calcium calms magnesium."