1. Principles of Pharmacotherapy in Acute Overdoses

Early toxin neutralization and enhanced elimination are foundational to managing acute overdoses. Rapid intervention within defined toxicity windows is critical to reduce the risk of irreversible organ injury. The decision to escalate from supportive care to more invasive measures like extracorporeal removal is guided by a comprehensive risk stratification that includes patient history, serum toxin levels, and clinical symptoms.

2. Antidotal Therapy

A. N-acetylcysteine (NAC) for Acetaminophen Overdose

NAC is a life-saving antidote that prevents hepatic necrosis by replenishing intracellular glutathione stores, which are essential for detoxifying the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI). It also has direct antioxidant and anti-inflammatory properties.

• Indications: Serum acetaminophen level above the treatment line on the Rumack–Matthew nomogram (e.g., >150 µg/mL at 4 hours post-ingestion); unknown ingestion time with evidence of liver injury; or high-risk patients (chronic ethanol use, malnutrition, pregnancy).
• Formulations: Intravenous (IV) is preferred in patients with vomiting, hepatic encephalopathy, or unreliable GI absorption. Oral is an alternative in stable patients but carries a risk of emesis and delayed delivery.
• Dosing Regimens:
  • IV (3-bag protocol): 150 mg/kg over 1 hour, followed by 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours (total 300 mg/kg).
  • Oral: 140 mg/kg loading dose, followed by 70 mg/kg every 4 hours for 17 doses.
• Monitoring: Acetaminophen levels at 4 hours post-ingestion and per institutional protocol. Monitor liver function tests (LFTs), INR, and renal function every 12–24 hours. Watch for anaphylactoid reactions (approximately 15% with IV NAC), which can be managed by slowing the infusion and administering antihistamines.

B. Sodium Bicarbonate for Salicylate Toxicity

Alkalinization with sodium bicarbonate is a key intervention that shifts salicylate from its lipid-soluble, non-ionized form to its water-soluble, ionized form. This “ion trapping” enhances renal clearance and, crucially, reduces its penetration into the central nervous system.

• Indications: Serum salicylate >30 mg/dL with symptoms (tinnitus, tachypnea) or >50 mg/dL regardless of symptoms; presence of metabolic acidosis.
• Dosing: An initial bolus of 1–2 mEq/kg IV, followed by a continuous infusion (e.g., 150 mEq in 1 L D5W) titrated to maintain a serum pH of 7.45–7.50 and a urine pH >7.5.
• Monitoring: Arterial blood gases (ABGs) every 1–2 hours initially, along with electrolytes (especially potassium) and volume status. Hypokalemia must be corrected, as it impairs the kidney’s ability to alkalinize urine.
• Role vs. Hemodialysis: Hemodialysis is the definitive treatment and should be initiated for severe toxicity (salicylate >100 mg/dL), acute kidney injury, refractory acidosis, or CNS deterioration (seizures, coma).

3. Gastrointestinal Decontamination

Activated charcoal (AC) can significantly reduce systemic absorption of certain toxins by adsorbing them within the GI tract. Its effectiveness is highly time-dependent.

• Indications: Ingestion of a charcoal-adsorbable toxin (most organic compounds) within 1 hour. Multi-dose activated charcoal (MDAC) may be beneficial for toxins with enterohepatic recirculation (e.g., theophylline, phenobarbital) or in extended-release formulations.
• Dosing: A single dose is 50–100 g for adults (0.5–1 g/kg for children). MDAC is typically dosed as 12.5 g/hour or 0.5 g/kg every 4 hours.
• Contraindications: Unprotected airway (risk of aspiration), ingestion of caustics or hydrocarbons, and known bowel obstruction.
• Pitfalls: Aspiration pneumonitis is a serious risk if the airway is not protected. Nasogastric tubes can become occluded if the charcoal slurry is not properly diluted and flushed.

4. Enhanced Elimination Techniques

Extracorporeal methods like hemodialysis (HD) and hemoperfusion are used to rapidly remove certain toxins from the bloodstream and correct severe metabolic disturbances. Selection is based on toxin properties such as volume of distribution (Vd) and protein binding.

• Modality Selection: HD is effective for small, water-soluble toxins with low protein binding (e.g., lithium, salicylates). Hemoperfusion, which passes blood over an adsorbent cartridge, is used for toxins with high affinity for the adsorbent (e.g., paraquat).
• Prescription: Requires a double-lumen dialysis catheter. Typical blood flow rates are 200–300 mL/min with a dialysate flow of 500 mL/min for a session of at least 4 hours.
• Monitoring: Pre- and post-treatment toxin levels are essential to confirm clearance. Monitor for rebound toxicity as the toxin redistributes from tissues back into the plasma; repeat sessions may be necessary.

5. Supportive Pharmacotherapy for Agent-Specific Toxicities

A. Theophylline Overdose

Theophylline toxicity causes a catecholamine surge and adenosine receptor antagonism, leading to refractory seizures and tachyarrhythmias.

• Management: Administer single-dose charcoal, followed by MDAC. Proceed to hemodialysis if the level is >100 µg/mL or if severe symptoms are present.
• Arrhythmias: Titrate an esmolol infusion (50–300 µg/kg/min) to a heart rate <100/min.
• Seizures: Use benzodiazepines as first-line therapy. Phenytoin is ineffective and should be avoided.
• Metabolic: Aggressively correct hypokalemia, hypomagnesemia, and hypophosphatemia.

B. Paraquat/Diquat Poisoning

There is no specific antidote for these highly lethal herbicides. Management focuses on immediate decontamination, early extracorporeal removal, and mitigating oxidative lung injury.

• Supportive Measures: Initiate charcoal hemoperfusion as early as possible. Use conservative oxygen therapy (target SpO₂ 88-92%) to avoid amplifying free radical production in the lungs. Aggressive fluid resuscitation is crucial.
• Monitoring: Closely monitor pulmonary status with imaging and oxygenation indices, as well as daily renal and hepatic function panels.

6. Special Populations and Dose Adjustments

Antidote and decontamination strategies must be tailored for patients with comorbid conditions, at the extremes of age, or with potential drug interactions.

• Renal Impairment: Use lower thresholds for initiating hemodialysis. In acetaminophen overdose with concurrent chronic kidney disease, the NAC infusion may need to be prolonged.
• Elderly: Reduced metabolic clearance may necessitate slower initiation and careful titration of antidotes like NAC, guided by serial LFT and INR trends.
• Pediatrics: Dosing is weight-based. For NAC, the IV loading dose is 150 mg/kg and the oral dose is 70 mg/kg every 4 hours. MDAC is typically 0.5 g/kg every 4 hours.

7. Monitoring and Follow-Up

Serial assessment of toxin levels and organ function is essential to guide the duration of therapy, detect rebound toxicity, and plan for a safe discharge.

• Serial Toxin Concentrations:
  • Acetaminophen: At 4, 16, and 24 hours post-ingestion, and until cleared.
  • Salicylates: Every 2–4 hours until levels are consistently decreasing and acidosis resolves.
  • Theophylline: Every 2 hours initially during acute management.
• Organ Function Tests: Monitor LFTs, INR, and creatinine every 12–24 hours. Obtain frequent ABGs during alkalinization therapy.
• Discharge Criteria: Toxin levels must be below treatment thresholds, with stable vital signs and organ function. Ensure patient education on medication safety and arrange for necessary follow-up labs.