[Pharmacokinetic aspects of the combination of interferon-alpha-2b and folic acid with fluorouracil].

The plasma levels of fluorouracil (5-fluorouracil, 5FU; CAS 51-21-8) after intravenous administration have been monitored without, under influence of interferon-alpha-2b (IFN) and under influence of IFN combined with folic acid (FA). IFN causes a highly significant change of the pharmacokinetic parameters of 5FU (p less than 0.001) compared to 5FU administration without IFN. The bioavailability of 5FU (compared as the AUC0-60 values) is elevated to 80%. In contrary, the combination of IFN with FA leads to a non-significant change of the 5FU pharmacokinetics, although the bioavailability is increased to 18%. The higher plasma levels of 5FU under the influence of IFN might be causes by a changed renal clearance, which is indicated by the reduction of the total plasma clearance at about 53%. The combination IFN/FA did not show a similar effect. Yet, in both cases an improvement of the tumor response and of the clinical picture could be observed.