Enhanced Elimination in Toxicology

Enhanced Elimination in Toxicology  Extracorporeal elimination

Extracorporeal elimination techniques require specialised staff, are invasive with significant risks of adverse events, and require specialised equipment and monitoring. They should only be undertaken in severe and life-threatening poisoning with appropriate toxicological and critical advice.

Haemodialysis: intermittent or continuous haemodialysis may be potentially beneficial in select poisonings based on the characteristics of the drug or toxin involved. In general, the drug or toxin needs to be a small molecule that has a small volume of distribution and slow elimination. In some cases, haemodialysis is beneficial for reasons other than removal of the drug or toxin, such as acidosis in metformin overdose where it is used to remove lactate.

Haemoperfusion: rarely used due to limited benefit in addition to haemodialysis and the limited availability of charcoal cartridges.

Plasmapheresis: despite numerous reports in the early literature there is no evidence for the use of plasmapheresis in the removal of drugs or toxins. There may be potential benefit for complications such as rhabdomyolysis.

The specific indications for extracorporeal techniques of elimination are discussed with the individual drugs and toxins and include:

• toxic alcohols: methanol and ethylene glycol

• anticonvulsants: valproate, carbamazepine

• theophylline

• lithium: chronic lithium poisoning in patients with acute renal failure

• metformin: removal of lactate

• methotrexate

• salicylates.

Urinary alkalinisation

Urinary alkalinisation has a limited role, which is only in poisoning by salicylates, methotrexate and some pesticides. Use:

	sodium bicarbonate 8.4% (= 1 mmol/mL) 1 mmol/kg IV as an initial bolus, then 25 to 50 mmol hourly as an IV infusion (100 mmol in 1000 mL of sodium chloride 0.9% at 250 mL/hour). The rate should be adjusted to maintain a urinary pH greater than 7.5.
	PLUS EITHER
1	potassium chloride 14 to 16 mmol orally, 3 times daily (child: 1 mmol/kg/day in 2 to 4 doses) [Note 1].
	OR
1	potassium chloride 10 to 20 mmol (= 0.75 to 1.5 g) IV, over 1 to 2 hours (child: 0.6 mmol/kg IV over 3 hours) preferably as a pre-mixed solution of the appropriate intravenous fluid. [Note 2].

Electrolytes should be monitored every four hours to monitor potassium and renal function. A dipstick urinalysis should be done regularly to make sure the urine remains alkaline.

Note 1: Effervescent immediate-release tablets of potassium contain 14 mmol potassium per tablet, and slow-release tablets contain 8 mmol potassium. The slow-release formulations of potassium are almost completely absorbed within one hour. Note 2: If pre-mixed IV solution is unavailable, potassium chloride concentrate injection must be added to a large volume of parenteral fluid and mixed thoroughly before infusion. The usual maximum concentration is 40 mmol/L.