Critical Antidotes & Reversal Agents
| Toxin / Drug | Specific Antidote / Reversal Agent | Mechanism / Key Clinical Clue |
|---|
| Acetaminophen | N-Acetylcysteine (NAC) | Replenishes hepatic glutathione reserves. Check Rumack-Matthew nomogram at 4 hours. |
| Opioids | Naloxone | Competitive mu-opioid receptor antagonist. Monitor for resedation. |
| Benzodiazepines | Flumazenil | GABA-A competitive antagonist. Caution: Can precipitate acute seizures in chronic users. |
| Warfarin | 4-Factor PCC + IV Vitamin K | 4-Factor Prothrombin Complex Concentrate rapidly restores Factors II, VII, IX, X, Protein C & S. |
| Heparin / LMWH | Protamine Sulfate | Positively charged base binds negatively charged heparin molecules. Partial reversal for LMWH. |
| Direct Oral Anticoagulants (DOACs) | Idarucizumab (for Dabigatran); Andexanet alfa (for Apixaban/Rivaroxaban) | Specific antibody fragments / decoy factor Xa. |
| Beta-Blockers | Glucagon (+ High-Dose Insulin Euglycemia) | Bypasses beta-receptors to increase myocardial cAMP via Gs protein activation. |
| Calcium Channel Blockers | IV Calcium Gluconate + High-Dose Insulin | Promotes myocardial calcium influx and metabolic fuel utilization. |
| Digoxin | Digoxin-specific Fab fragments | Indicated for malignant arrhythmias, K+ > 5.0 mEq/L, or ingestions > 10 mg. |
| Tricyclic Antidepressants (TCAs) | IV Sodium Bicarbonate (NaHCO3) | Overcomes fast sodium channel blockade and alkalinizes serum to decrease active free drug. |
| Ethylene Glycol / Methanol | Fomepizole (or Ethanol) | Competitive inhibitor of alcohol dehydrogenase; prevents toxic metabolite generation. |
| Organophosphates (Cholinergic) | Atropine (first) + Pralidoxime (2-PAM) | Atropine reverses muscarinic hyperstimulation; 2-PAM regenerates acetylcholinesterase at nicotinic synapses. |
Cytochrome P450 Interactions
Major CYP450 Inhibitors (Increase substrate levels → toxicity)
- SICKFACES.COM: Sodium valproate, Isoniazid, Cimetidine, Ketoconazole (Azoles), Fluconazole, Alcohol (acute binge), Chloramphenicol, Erythromycin/Clarithromycin, Sulfonamides, Ciprofloxacin, Omeprazole, Metronidazole, Grapefruit juice.
Major CYP450 Inducers (Decrease substrate levels → therapeutic failure)
- CRAP GPS: Carbamazepine, Rifampin, Alcohol (chronic), Phenobarbital, Griseofulvin, Phenytoin, St. John’s Wort.
See the full High-Yield Drug Interaction Lookup Matrix for searchable CYP450, P-gp, QT, and toxicity pairs with mechanism, consequence, and next step.
High-Yield Anticoagulant Principles & HIT Management
Heparin["Patient Receiving Heparin / LMWH"] --> Drop{"Platelet Count Drops >50% or Nadir <100k at Days 5-10?"}
Drop -- "YES (Suspected HIT Type II)" --> Action1["1. STOP all Heparin products immediately"]
Action1 --> Action2["2. Send PF4-Heparin ELISA + Serotonin Release Assay (SRA)"]
Action2 --> Action3["3. Initiate non-heparin Direct Thrombin Inhibitor: ARGATROBAN or BIVALIRUDIN (or Fondaparinux)"]
Action3 --> Avoid["AVOID:\n• Platelet transfusion (causes arterial 'white clot' thrombosis)\n• LMWH (100% cross-reactivity)\n• Early Warfarin (causes microvascular thrombosis & skin necrosis via Protein C depletion)"]
Antibiotic Selection Nuances in Special Populations
| Clinical Presentation | First-Line Regimen | Major Drug Trap to AVOID |
|---|
| Community-Acquired Pneumonia in Pregnancy | Ceftriaxone + Azithromycin (or Amoxicillin-Clavulanate + Azithromycin) | Fluoroquinolones (cartilage toxicity / arthropathy) and Doxycycline (bone growth retardation, tooth discoloration). |
| Domestic Cat Bite (Pasteurella multocida) | Amoxicillin-Clavulanate (Augmentin) | Cephalexin, Ciprofloxacin, Clindamycin (lack adequate Pasteurella coverage). |
| Uncomplicated Cystitis in 1st Trimester Pregnancy | Nitrofurantoin, Cephalexin, or Fosfomycin | TMP-SMX (neural tube defect antifolate in 1st trimester; kernicterus in 3rd trimester) and Fluoroquinolones. |
| Acute Gout Flare with Severe Chronic Kidney Disease | Intra-articular Corticosteroid or Oral Prednisone | NSAIDs (Indomethacin) (precipitates acute renal failure) and Colchicine (neuromyopathy / toxicity with GFR < 30). |