Is there a circadian variation in plasma concentrations of etoposide given by prolonged continuous infusion?

The prolonged continuous infusion of low-dose etoposide is a new approach to treating cancer. Whether or not a circadian variation in the plasma levels of etoposide existed was investigated in nine patients with non-small-cell lung cancer. Etoposide was infused for 14 days and blood samples were obtained every 4 h for 1 day. There was no significant circadian variation, and the observed small within-day variations seemed to lack clinical significance.