What factors determine if a drug is effectively removed by extracorporeal therapies?
There are clinical situations where an overdose or intoxication with certain drugs warrants removal with an extracorporeal therapy such as hemodialysis (HD) or continuous venovenous hemofiltration (CVH).
Efficient drug removal by extracorporeal therapies is determined primarily by:
- • Drug characteristics associated with efficient removal
- Small molecular weight (<10,000 Da)
- Limited protein binding (<50%)
- Small volume of distribution (<1.0 L/kg, which suggests the drug is limited to the plasma space or extracellular space)
- Water versus lipid solubility
- • Dialyzer characteristics associated with efficient clearance
- Large surface membrane
- Large pore size
- High blood flow rates
- High dialysate flow rates
Examples of drugs efficiently removed by HD include the toxic alcohols, lithium, metformin, theophylline, and salicylates. CVVH is inferior to HD due to its low drug clearance, which is primarily determined by the lower blood flow rates and dialysate flow rates employed with this extracorporeal modality.
CVVH does have a role to treat drug rebound following HD for drugs such as lithium, metformin, and methotrexate.