Intrathecal administration of topotecan in nonhuman primates

The cerebrospinal fluid (CSF) pharmacokinetics of topotecan were studied in a nonhuman primate model following intraventricular administration of 0.1 mg. Lactone and total drug concentrations were measured using a reverse-phase HPLC method with fluorescence detection. The mean peak concentrations of lactone and total drug in ventricular CSF were 83±18 M and 88±25 M, respectively. CSF drug elimination of the lactone was bi-exponential with a terminal half-life of 1.3 h. The mean clearance from ventricular CSF was 0.075 ml/min for the lactone and 0.043 ml/min for total drug. The ventricular CSF drug exposure (AUC) to lactone was 450-fold greater following intraventricular administration of 0.1 mg topotecan than after systemic intravenous administration of a 40-fold higher dose (10 mg/m²). Peak lumbar concentrations (n=1), which occurred 2 h after intraventricular drug administration, were 0.98 M and 2.95 M for the lactone and total drug, respectively. A transient CSF pleocytosis was observed in one animal following intraventricular topotecan administration and in one animal following intralumbar topotecan administration. No other acute or chronic neurologic or systemic toxicities were observed following a single intraventricular dose or weekly (×4) intralumbar topotecan. Compared with systemic topotecan, intrathecal administration provided a significant pharmacokinetic advantage in terms of CSF drug exposure and did not produce any significant neurotoxicity in a nonhuman primate model. Intrathecal topotecan should be evaluated clinically as a potential alternative therapy for refractory meningeal tumors.Pediatric Branch, National Cancer Institute, Building 10 Room 13N240, 9000 Rockville Pike, Bethesda, MD 20892, USA