Charcoal hemoperfusion in the treatment of phenytoin overdose

In the case of phenytoin, a drug that is generally highly protein bound, there is a lack of consensus on the use of charcoal hemoperfusion in cases of overdose. We performed charcoal hemoperfusion on a phenytoin-overdosed patient to assess the effectiveness of this treatment. The plasma concentrations of total and free phenytoin fell rapidly, from 40.0 microg/mL and 3.6 microg/mL to 16.2 microg/mL and 1.5 microg/mL, respectively, after 3 hours of hemoperfusion. The total phenytoin elimination half-life was 3.9 hours. The fraction of protein-bound phenytoin was constant (90.8% +/- 0.5%) before, during, and after the procedure. The relations between the in vitro protein binding and adsorption of phenytoin to activated charcoal were also examined. Interestingly, bound phenytoin was found to dissociate from plasma proteins in the presence of activated charcoal and subsequently became adsorbed to the activated charcoal. Considering that phenytoin is bound to albumin with a large number of binding sites (n = 6) and a small binding constant (K = 6 x 10(3/)mol/L), the extent of adsorption to activated charcoal may depend on the magnitude of the binding constant of the drug to plasma proteins. The current results suggest that charcoal hemoperfusion is effective for the removal of drugs that bind to plasma proteins with a low binding constant.