Pharmacokinetic study of weekly (days 1-5) low-dose S-1 in patients with non-small-cell lung cancer

S-1, an oral fluoropyrimidine, is usually given for 4 weeks (80 mg/m2/day) followed by a 2-week rest. However, compliance with this regimen is unsatisfactory because of adverse events such as leukopenia, anorexia, and nausea. To reduce adverse effects and improve compliance, we studied a "5-day on/2-day off" low-dose regimen of S-1 and evaluated pharmacokinetics in patients with non-small-cell lung cancer (NSCLC).

Twelve patients with NSCLC were divided into 2 groups and received S-1 in a dose of 25 mg twice daily (level 1, n = 6) or 40 mg twice daily (level 2, n = 6) for 5 consecutive days followed by a 2-day rest (5 days on/2 days off) every week. Plasma 5-fluorouracil (5-FU) concentrations were measured.

The maximum concentration in plasma and the area under the plasma concentration-time curve from 0 to 9 h were respectively 55.3 ± 21.1 ng/ml and 290.2 ± 95.7 ng·hr/ml for level 1, as compared with 104.2 ± 33.5 ng/ml and 541.9 ± 232.3 ng·hr/ml for level 2. These values were similar to those previously reported for a continuous intravenous infusion of 5-FU. Adverse events were grade 1 fatigue (n = 1 in each group) and anorexia (n = 1 in each group).

A "5-day on/2-day off" low-dose (40 mg twice daily) regimen of S-1 is feasible for the treatment of NSCLC, with acceptable plasma 5-FU concentrations and minimal adverse effects. A phase II or III trial of this regimen in an adjuvant setting is warranted in patients with NSCLC.