Monday, December 12, 2011

TOPIC DISCUSSION: Lithium and timing of dialysis?

Since 1870s, lithium has been around to help physicians deal with many issues including gout, cluster headaches and neutropenia.  Then it became the standard of care treatment for bipolar disorder.  This agent is water soluble and not protein bound hence easily dialyzed.
What are the indications for dialysis in a patient who comes in with lithium toxicity?

1. Lithium toxicity and acute renal injury
2. Patients with normal renal function and cannot tolerate aggressive fluid therapy or GI decontamination due to either cardiac or liver disease
3. Severe neurological presentations of altered mental status and seizures.
4. Acute presentation with even mild symptoms but level >4.0mEq/L
5. Chronic use of lithium but level >2.5mEq/L
6. Be careful of rebound phenomenon as it is released from adipose tissue as being removed by dialysis.

Points 4+5 might be controversial as many won't believe in just using a number to arbitrarily start dialysis. There are also some who have advocated CVVH in this setting as it will prevent the rebound regardless of the volume status of the patient. Some might argue that if presenting acutely, to just hydrate and follow serial levels ask lithium follows a two compartment model. Its initially high in the blood and then high in the tissue. Dialysis won't be effective in removing the intracellular lithium.  As a result, early levels could be misleading.

Lets go through an exercise of why dialysis is so effective in removing lithium. It has to do with the volume of distribution(Vd). It is the amount of drug/ plasma concentration.  Or L/kg.  Some drugs such as opioids and anti depressants have large Vd and lithium, alcohols and salicylate have small Vd.

So think of this way: If your clearance is 200ml/min using dialysis or native GFR of 100ml/min
and you have a drugA with 500L of Vd and another with 50L of Vd( lithium).  Then the fractional elimination in 60 min of dialysis will be 1% for drugA and 17% for drug B (Half life is 0.693 Vd/Clearance)

1 comment:

  1. I did not understand how you got the above result. Can you please go through the steps? thanks


All Posts

Search This Blog