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The objective of this study was to evaluate the plasma and serum concentrations of cytarabine (CA) administered via constant rate infusion (CRI) in dogs with meningoencephalomyelitis of unknown etiology (MUE). Nineteen client-owned dogs received a CRI of CA at a dose of 25 mg/m 2 /h for 8 h as treatment for MUE. Dogs were divided into four groups, those receiving CA alone and those receiving CA in conjunction with other drugs. Blood samples were collected at 0, 1, 8, and 12 h after initiating the CRI. Plasma (n = 13) and serum (n = 11) cytarabine concentrations were measured by high-pressure liquid chromatography. The mean peak concentration (C MAX ) and area under the curve (AUC) after CRI administration were 1.70 ± 0.66 μg/mL and 11.39 ± 3.37 h·μg/mL, respectively, for dogs receiving cytarabine alone, 2.36 ± 0.35 μg/mL and 16.91 + 3.60 h·μg/mL for dogs administered cytarabine and concurrently on other drugs. Mean concentrations for all dogs were above 1.0 μg/mL at both the 1- and 8-h time points. The steady-state achieved with cytarabine CRI produces a consistent and prolonged exposure in plasma and serum, which is likely to produce equilibrium between blood and the central nervous system in dogs with a clinical diagnosis of MUE. Other medications commonly used to treat MUE do not appear to alter CA concentrations in serum and plasma., (© 2016 John Wiley & Sons Ltd.)

Levetiracetam (LEV) is a commonly used add-on medication in dogs with refractory epilepsy. The objective of this study was to determine if the pharmacokinetics of LEV are altered by concurrent administration of phenobarbital (PB). Six healthy dogs received a single oral dose of LEV (16.7-27.8 mg/kg). Blood samples were collected at baseline and intermittently for 24 h. The study was repeated after the dogs received oral PB (2.0-3.3 mg/kg) twice daily for 21 days. Plasma LEV levels were evaluated by high pressure liquid chromatography, and data analyzed using a compartmental model. Compared with values determined when LEV was administered alone, concurrent administration of PB resulted in a decrease in LEV peak concentration (C(max) ) from 32.39 ± 6.76 to 18.22 ± 8.97 (P = 0.0071), a decrease in elimination half-life (T(1/2) ) from 3.43 ± 0.47 to 1.73 ± 0.22 (P = 0.0005), and an increase in oral clearance from 124.93 ± 26.93 to 252.99 ± 135.43 ml/h/kg (P < 0.0001). Concurrent PB administration significantly alters the pharmacokinetics of LEV in the dog, indicating that dosage adjustments might be necessary when the drug is administered with PB., (© 2010 Blackwell Publishing Ltd.)