The Effects of Exchange Transfusion on the Pharmacokinetics of Phenobarbital

A 26-month-old child was admitted to the pediatric intensive care unit for treatment of apparent fulminant hepatitis. While hospitalized, he underwent eight exchange transfusions to decrease ammonia concentrations. The patient received intravenous phenobarbital (Pb) for the treatment of cerebral edema. To determine the effects of exchange transfusion on Pb clearance, serum Pb concentrations were obtained before, after, and between exchanges. Preexchange and postexchange serum Pb concentrations were obtained on three separate exchanges. Pb concentrations also were examined between two exchange transfusions. The amount of Pb actually removed during one exchange transfusion was determined by analyzing serum obtained from the discarded blood resulting from the procedure. All Pb concentrations were analyzed by the Emit system. Results indicate that Pb was cleared at a mean rate of 433 ml/h during the exchange periods examined, with a mean overall elimination constant of 0.20 h−1. The Pb actually removed by the exchange transfusion on day 10 of hospitalization was determined to be 17 mg, while the calculated amount was 8 mg. A mean of 22.3 mg of Pb was calculated to be removed over an average exchange time of 2.2 hours. Pb clearance during exchange transfusion has not been reported previously. This case has shown that small amounts of Pb can be removed by exchange transfusion; therefore, patients undergoing this procedure may require serum monitoring after exchange.