Clinical pharmacokinetics of vinorelbine

Vinorelbine (5'-noranhydrovinblastine) is a recently developed semisynthetic anticancer drug which belongs to the Catharanthus alkaloid family. Its mechanism of action is only partially known but it is assumed that it acts, like vinblastine and vincristine, as an antimicrotubule agent arresting cell division in mitosis. Clinically, vinorelbine has mainly shown activity in the treatment of advanced non-small-cell lung cancer and the treatment of metastatic breast cancer. Early pharmacokinetic data were obtained with radioactive assays (radio-immunoassay or 3H-labelled vinorelbine), then with more selective high performance liquid chromatographic techniques. Vinorelbine is usually administered intravenously but there has also been some experimentation with an oral formulation. The bioavailability of a liquid filled gelatin capsule ranges between 12 and 59% with a mean value of 27% [standard deviation (SD) 12%]. Vinorelbine is rapidly absorbed with peak serum concentration reached within 2 hours. In vitro, vinorelbine is mainly distributed into the blood cells, especially platelets (78%) and lymphocytes (4.8%) The unbound blood fraction is around 2%. In lung tissue vinorelbine concentrations are much higher than in serum, by up to 300-fold 3 hours after administration. Little is known about the biotransformation of vinorelbine. Desacetylvinorelbine is considered to be a minor metabolite and is only found in urine fractions, representing 0.25% of the injected dose. Urinary excretion of vinorelbine is low, accounting for less than 20% of the dose. Faecal elimination has been demonstrated in 2 patients who were administered 3H-labelled vinorelbine; the amount of radioactivity recovered in the faeces was 33.9 and 58.4% for the 2 patients, respectively. The pharmacokinetic profile of vinorelbine is often described as a 3-compartment model characterised by a long terminal half-life (t1/2) that varies between 20 and 40 hours and a large apparent volume of distribution (Vd) of around 70 L/kg. Systemic clearance ranges between 72.54 and 89.46 L/h (1209 and 1491 ml/min) when determined by high performance liquid chromatography and is higher than that reported by radioimmunoassay [46.2 L/h (770 ml/min)]. This could be due to the greater specificity of the chromatographic method. Vinorelbine has been administered by continuous intravenous infusion over 4 days. Steady-state was reached and the concentrations obtained were above the in vitro IC50 (concentration of drug causing 50% inhibition). The effect of liver disease on vinorelbine pharmacokinetics has been studied in patients with breast cancer. Patients with massive secondary liver disease had a lower systemic clearance than those who have no liver disease or a lesser invasion. In children, vinorelbine seems to display a shorter t1/2 (14.7 hours) than that found in adults. In addition, the systemic clearance is highly variable [from 12 to 93.96 L/h/m2 (200 to 1566 ml/min/m2)]. Vinorelbine is often co-administered with cisplatin in the treatment of advanced non-small-cell lung cancer. The disposition of the alkaloid is not altered by concurrent administration of cisplatin.