to hours By using a nearly continuous stream of fresh charcoal that descends through the intestinal tract, a constant concentration gradient is maintained that favors the back diffusion of free drug from periluminal capillary blood into the intestinal lumen, where it may be bound immediately to the newer charcoal, so the free drug concentration in the intestinal lumen remains low In addition, enterohepatic recirculation of some drugs may be interrupted as reabsorption from bile is prevented To be safe and effective, this technique requires active peristalsis and an intact gag reflex or a protected airway Common pediatric poisonings for which repetitive charcoal dosing may be considered include phenobarbital, carbamazepine, phenytoin, digoxin, salicylates, and theophylline Cathartics, such as sorbitol, should be administered no more frequently than every third dose Renal Replacement Therapy Renal replacement therapy is indicated for selected cases of severe poisoning to enhance toxin clearance and correct severe acid–base or electrolyte disturbances High-flux hemodialysis is the modality of choice for expeditious toxin removal Other methods such as exchange transfusion, plasmapheresis and peritoneal dialysis are much less effective in rapidly reversing the course of poisoning Hemoperfusion, the process of passing blood through a dialysis circuit containing an adsorbent column, was historically used to remove higher–molecular-weight substances that could not be extracted through standard dialysis but has become obsolete since the arrival of newer high-flux dialysis membranes Continuous renal replacement therapy, such as continuous venovenous hemodiafiltration (CVVHDF), also has much slower rates of toxin removal and should be reserved for the hemodynamically unstable patient who cannot tolerate conventional HD Acute extracorporeal removal should be considered in light of patient- and drug-related criteria Patient-related criteria include (i) anticipated prolonged coma with the high likelihood of attendant complications, (ii) development of renal failure or impairment of normal excretory pathways, and (iii) progressive clinical deterioration despite other medical therapy Drug-related criteria are (i) serum concentrations in the potentially fatal range of a dialyzable substance, (ii) a correlation between serum drug concentration and toxicity, and (iii) anticipated clinical benefit from faster toxin removal than what would be expected from endogenous clearance Dialysis is most useful for drugs with low volumes of distribution (less than L/kg), low–molecular-weight (less than 500 Da), and low protein binding, including salicylic acid, methanol, ethylene glycol, lithium, and theophylline Other conditions which may be amenable to extracorporeal removal