1. Modality Selection Based on Toxin Characteristics

The cornerstone of effective extracorporeal therapy in toxicology is tailoring the modality to the specific properties of the toxin and the clinical status of the patient. Key factors include molecular weight (MW), volume of distribution (Vd), and protein binding.

2. Pharmacokinetic Optimization of Extracorporeal Clearance

Maximizing toxin removal requires careful adjustment of blood flow, dialysate/replacement fluid rates, and selection of appropriate membranes or cartridges. These settings directly influence the efficiency of diffusive and convective clearance.

3. Concomitant Medication Dosing Adjustments

Extracorporeal therapies are non-selective and will clear co-administered medications, particularly those with low volume of distribution and low protein binding. Dosing must be adjusted to prevent subtherapeutic levels, especially for critical drugs like antibiotics and anticonvulsants.

Predicting Drug Removal

• High Clearance Expected: Drugs with low Vd (<0.2 L/kg) and low protein binding (<20%). Examples include aminoglycosides, some beta-lactams, and digoxin.
• Low Clearance Expected: Drugs with high Vd and/or high protein binding. These drugs are sequestered in tissues or bound to albumin and are less available for removal.

The Rebound Phenomenon

After a session of IHD, toxin levels in the plasma can rebound as the substance redistributes from tissues back into the central compartment. This is particularly notable with lithium. Management may require scheduled repeat sessions or switching to a continuous therapy like CRRT.

Therapeutic Drug Monitoring (TDM)

TDM is essential for guiding therapy. A typical protocol involves drawing drug levels pre-session, immediately post-session, and again 4–6 hours later to assess for rebound and determine the need for supplemental dosing. Continuous infusions of time-dependent antibiotics (e.g., beta-lactams) are often preferred during CRRT to maintain stable concentrations above the MIC.

4. Vascular Access and Anticoagulation Strategies

Reliable vascular access and effective anticoagulation are foundational to successful extracorporeal therapy, minimizing circuit downtime and complications.

5. Monitoring Plan for Efficacy and Safety

A structured monitoring plan is crucial to track toxin removal, prevent complications, and ensure patient stability throughout the therapy.

6. Pharmacotherapy: Multiple-Dose Activated Charcoal (MDAC)

MDAC is a non-invasive method that enhances toxin elimination by interrupting enterohepatic or enteroenteric recirculation. It works by adsorbing toxins secreted into the GI tract, preventing their reabsorption.

• Mechanism: The porous carbon matrix of activated charcoal provides a large surface area for adsorbing toxins within the gut lumen.
• Indications: Most effective for lipophilic toxins with prolonged absorption or significant enterohepatic cycling, such as carbamazepine, theophylline, dapsone, phenobarbital, and quinine.
• Dosing Regimen: An initial dose of 50–100 g is followed by 12.5–25 g every 2–4 hours. Therapy is typically continued for 12–24 hours.
• Monitoring and Safety: The airway must be protected to prevent aspiration pneumonitis. Monitor for abdominal distension and ensure bowel sounds are present.
• Contraindications: Ileus, bowel obstruction or perforation, and an unprotected airway are absolute contraindications.
• Pitfalls: The routine co-administration of sorbitol with each dose is discouraged as it can cause significant fluid shifts and electrolyte disturbances without proven benefit.

7. Pharmacoeconomic Considerations

The choice of modality must be aligned with institutional resources, staffing capabilities, and cost constraints without compromising essential patient care. Standardized, protocolized pathways can optimize resource utilization.

• IHD: Lower cost of disposables and requires fewer nursing hours per treatment. However, rebound may necessitate multiple sessions, increasing overall cost.
• CRRT: Higher costs associated with equipment, continuous fluids, and intensive nursing. May potentially reduce overall ICU length of stay by providing continuous, stable clearance.
• Hemoperfusion: Cartridges are very expensive. This cost may be justified if it significantly shortens the duration of therapy and ICU stay for specific, life-threatening poisonings.
• MDAC: The drug itself is inexpensive, but administration is labor-intensive and requires close monitoring, which increases personnel costs.