The objective of this study was to determine the influence of pleural and
ascitic fluid on the pharmacokinetics of the antitumor camptothecin
derivative topotecan. Four patients with histological proof of malignant
solid tumor received topotecan (0.45 or 1.5 mg/m2) p.o. on several
occasions in both the presence and absence of third space volumes. Serial
plasma and pleural or ascitic fluid samples were collected during each
dosing and analyzed by high-performance liquid chromatography for both the
intact lactone form of topotecan and its ring-opened carboxylate form. The
apparent topotecan clearance demonstrated substantial interpatient
variability but remained unchanged within the same patient in the presence
[110 +/- 55.6 liters/ h/m2 (mean +/- SD of eight courses)] or absence of
pleural and ascitic fluid [118 +/- 31.1 liters/h/m2 (mean +/- SD of seven
courses)]. Similarly, terminal half-lives and area under the
concentration-time curve ratios of lactone:total drug in plasma were
similar between courses within each patient. Topotecan penetration into
pleural and ascitic fluid demonstrated a mean lag time of 1.61 h (range,
1.37-1.86 h), and ratios with plasma concentration increased with time
after dosing in all patients. The mean ratio of third space topotecan
total drug area under the concentration-time curve to that in plasma was
0.55 (range, 0.26-0.87). These data indicate that topotecan can be safely
administered to patients with pleural effusions or ascites and that there
is substantial penetration of topotecan into these third spaces, which may
prove beneficial for local antitumor effects
