Pharmacokinetics of intrathecal gemcitabine in nonhuman primates.

PURPOSE: Gemcitabine is an excellent candidate for regional therapy. We quantified cerebrospinal fluid (CSF) and plasma concentrations of gemcitabine and its inactive metabolite, 2',2'-difluorodeoxyuridine (dFdU), in nonhuman primates given intrathecal gemcitabine. EXPERIMENTAL DESIGN: Three nonhuman primates received 5 mg of gemcitabine via lateral ventricle. CSF was sampled from the fourth ventricle in all of the animals and the lumbar space in one, and one had plasma sampled. One animal had ventricular CSF sampled after receiving 5 mg intralumbar gemcitabine. Gemcitabine and dFdU were measured by high-performance liquid chromatography. Three additional animals had 5 mg intralumbar gemcitabine administered weekly for 4 weeks and were monitored for toxicity. RESULTS: At 37 degrees C in vitro, gemcitabine was stable in CSF. Ventricular delivery of gemcitabine produced peak ventricular CSF gemcitabine concentrations of 297 +/- 105 microg/ml. After 6 h, the concentrations were <0.03 microg/ml. Intrathecal gemcitabine was rapidly and extensively converted to dFdU. CSF dFdU concentrations increased to 82 microg/ml at 1 h and then declined to very low values by 24 h. After intraventricular administration, CSF gemcitabine and dFdU area(s) under the curve (AUC) were 251 +/- 85 and 249 +/- 88 microg/ml x h. Intralumbar gemcitabine produced lower ventricular CSF gemcitabine and dFdU concentrations than did intraventricular gemcitabine. The plasma gemcitabine AUC associated with 5 mg of intraventricular gemcitabine was 2 mg/ml x h, which was >200-fold lower than the CSF gemcitabine AUC in the same animal. Transient CSF pleocytosis was the only toxicity observed. CONCLUSIONS: Our results demonstrate a large pharmacokinetic advantage of intrathecal gemcitabine and support a planned Phase I clinical trial of this dosing strategy.

Plasma and cerebrospinal fluid pharmacokinetic study of BNP1350 in nonhuman primates.

PURPOSE: BNP1350 (7-[(2-trimethylsilyl)ethyl]-20(S)-camptothecin, karenitecin), a highly lipophilic camptothecin, a high percentage of which is maintained in the active lactone form under physiologic conditions, has recently entered clinical trials in adults and children. BNP1350 has shown significant preclinical antitumor activity against a wide variety of adult and pediatric tumor cell lines. This study was undertaken to define the pharmacokinetics of BNP1350 in both plasma and cerebrospinal fluid (CSF) in a nonhuman primate model. METHODS: Four nonhuman primates with indwelling Ommaya reservoirs received BNP1350, 0.1 mg/kg i.v, administered as a 60-min infusion. Frequent plasma and CSF samples were obtained for quantitation of BNP1350 concentrations using reverse-phase high-pressure liquid chromatography (HPLC). RESULTS: Disappearance of the lactone form from the plasma was biexponential with a mean distribution half-life of 57.5 min (CV +/-33%) and an elimination half-life of 457 min (CV +/-24%). The volume of distribution for the central compartment was 1.36 l/kg (CV +/-27%) and clearance from the central compartment was 10.6 ml/kg per minute (CV +/-28%). The peripheral compartment volume of distribution was 1.96 l/kg (CV +/-8.4%). Peak CSF lactone concentration, which occurred at 12 to 25 min after the end of the infusion, was 0.33 n M (CV +/-71%). CONCLUSIONS: The ratio of the CSF AUC to the plasma AUC was less than 5% (range 0.4% to 3.0%), similar to other highly protein-bound topoisomerase inhibitors such as 9-aminocamptothecin and SN-38 (the active metabolite of irinotecan).