Cytosine arabinoside (ara-C) is a component of many protocols for the treatment of CNS (central nervous system) leukemia and lymphoma in humans and dogs. It is also used for the prophylaxis of CNS metastasis in acute lymphoblastic leukemia. Although ara-C enters the cerebrospinal fluid (CSF) of human cancer patients after i.v. administration, it is unclear whether a similar CNS distribution occurs in humans whose blood-brain barrier has not been compromised by invasive disease. No information on the penetration of ara-C into the CSF in dogs is available. We studied the plasma and CSF pharmacokinetics of 600 mg/m2 ara-C in ten healthy male dogs after its administration as a rapid i.v. bolus (six dogs) or as a 12-h i.v. infusion (four dogs). Ara-C concentration in blood and CSF samples was determined by high-performance liquid chromatography (HPLC). After an i.v. bolus of ara-C, the mean plasma distribution half-life was 7.1 +/- 4.5 min and the mean elimination half-life was 69 +/- 28 min. The mean plasma clearance was 227 +/- 125 ml min-1 m-2. The peak concentration of ara-C in the CSF was 29 +/- 11 microM, which occurred at 57 +/- 13 min after the ara-C bolus. The CSF elimination half-life was 113 +/- 26 min. During a 12-h infusion of ara-C (50 mg m-2 h-1), the plasma steady-state concentration was 14.1 +/- 4.2 microM, the CSF steady-state concentration was 8.3 +/- 1.1 microM, and the CSF: plasma ratio was 0.62 +/- 0.14. The plasma elimination half-life was 64 +/- 19 min and the plasma clearance was 214 +/- 69 ml min-1 m-2. The CSF elimination half-life was 165 +/- 28 min. No clinically significant toxicity was observed over a 21-day period following drug administration in either of the treatment groups. Our data indicate that ara-C crosses the blood-brain barrier in normal dogs and that i.v. administration of this drug has potential as a treatment modality for neoplasia involving the CNS.

Summary Endotoxin (LPS) was quantitated in experimental subjects and in horses with naturally occurring gastrointestinal strangulation obstruction and/or septicaemic diseases to establish the fate of LPS and the clinical usefulness of the Limulus amoebocyte lysate (LAL) assay. The assay was validated for sensitivity (10 pg/ml), recovery (90 to 106 per cent), intra‐assay precision (CV = 5.5 per cent) inter‐assay precision (CV = 11 per cent), and stability of diluted, heat treated, frozen samples (at least 90 days). Plasma concentrations of LPS after sublethal (3 μg/kg) jugular or portal vein bolus injections of LPS rose to 4000 pg/ml and 1500 pg/ml respectively followed by a rapid phase of clearance. Peak plasma concentrations of LPS, associated with slow portal infusion, were lower than peak values associated with bolus injections, remained elevated during the infusion (2 h), but rapidly decreased after infusion was stopped. Thirty seven horses with 38 episodes of naturally occurring gastrointestinal or septicaemic disease were assayed for LPS. Eight episodes involving gastrointestinal disease and eight involving septicaemic disease were positive for LPS. It is concluded that the LAL assay is sensitive and reliable for detecting LPS in equine plasma and it may have clinical value for establishing the severity of endotoxaemia or for distinguishing between septic and non‐septic conditions. Problems of rapid clearance of LPS from plasma, low concentrations, the possibility of sample contamination, and the time and method of sample procurement remain to be addressed.

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