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 rapid: maximum 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 i.v. injections. Bioavailability (i.v./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.