Oral administration of [3H]navelbine in patients: comparative pharmacokinetics using radioactive and radioimmunologic determination methods

[3H]Navelbine (NVB) was administered orally to two patients. Drug levels in biological fluids were monitored by radioimmunoassay (RIA) and direct radioactivity (RA) determinations. NVB absorption was rapidmaximum plasma concentrations appeared in the first 2 h after oral administrations. Pharmacokinetic parameters estimated from RIA data were in complete accordance with those obtained from iv injections. Bioavailability (iv/po) estimated from RIA and RA data averaged 40.6 and 93.0%, respectively. NVB urine excretion was low. Fecal excretion remained its main elimination route. Moreover, large differences were observed in area under NVB plasma concentration-time curve (AUC) values obtained by the two methods, implying intense drug bio-transformations.