A 68 y/o patient presents to the ER with an accidental overdose of their prescription medication. The staff has tried the usual measures like activated charcoal, gastric lavage, etc. but with little improvement. The medical student mentions acute hemodialysis as an option. The toxicology references you have do not list anything regarding dialysis as a potential option.

What data would allow you come to a rational decision regarding the use of acute hemodialysis in the patient?
 

** THANKS to MAJ (Dr.) Chris Glanton for his help with this Pearl**

Obviously, the best information would be to have a literature reference or textbook listing if and how much is removed by dialysis. We don’t have that luxury in this case but should be some physical and pharmacokinetic properties available with which you could come to a reasonable decision.

Volume of distribution (Vd) – the larger the volume of distribution, the less effective the hemodialysis. Vd is a theoretical volume used in pharmacokinetic calculations, estimating the extent of the drug’s distribution within the body. For example, digoxin has a Vd of 6L/kg (very large) because it’s distributed into muscle. Dialysis only clears the vascular volume (about 3L) or slightly more.

Molecular weight (MW) – lower molecular weight agents are more easily dialyzable. Unfractionated heparin is a very large protein molecule (about 15,000 daltons, range 5,000 to 30,000 daltons) and NOT dialyzable. Lithium, a cation with a very low molecular weight, is more easily dialyzable. The smaller MW compounds may pass more easily through the semi permeable membrane filter in the dialyzer.

Water solubility – the more water-soluble the drug, the more likely it will be cleared via hemodialysis. Again, lithium is very water soluble and removed well via hemodialysis.

Protein binding – highly protein bound drugs are NOT easily dialyzed. For example warfarin and phenytoin are ~ 98-99% protein bound to albumin and other serum protein and not well dialyzed.

A list of agents removed effectively by hemodialysis include (but are not limited to) lithium, ethanol, ethylene glycol, methanol, salicylates, and theophylline. Remember, dialysis carries it’s own risk and its’ use in overdoses is probably best considered at least a second line agent. Dialysis should be considered when 1) the duration of the symptoms maybe prolonged or are refractory to other treatment modalities, 2) other routes of excretion are unavailable or do not provide rapid enough clearance of the offending agent, 3) clinical deterioration is evident, 4) the drug is dialyzable, and 5) the appropriate personnel and equipment are available.

Charcoal hemoperfusion was used in the past to quickly remove toxins but has fallen from favor due to poor results, inappropriate use, and limited availability.