Dilution of maropitant (Cerenia) in lactated Ringer solution prolongs subcutaneous drug absorption and reduces maximum plasma concentration

OBJECTIVE The aim of this study was to determine whether the pharmacokinetics of maropitant, administered SC as a commercially available maropitant-containing injectable product (Cerenia Injectable), differ when combined with lactated Ringer solution prior to administration. ANIMALS We used 6 adult spayed female Beagle dogs between 3 and 6 years of age, with a mean weight of 9.58 kg. PROCEDURES In this randomized crossover study, the dogs underwent 2 treatment protocols separated by a 14-day washout period: (1) an SC injection of 1 mg/kg of Cerenia Injectable (maropitant citrate; 10 mg/mL) and (2) 1 mg/kg of Cerenia Injectable diluted in 10 mL/kg of lactated Ringer injectable solution (LRS) given SC. Plasma maropitant concentrations were assessed by mass spectrometry. Pharmacokinetic analysis was performed using pharmacokinetic and pharmacodynamic data-analysis software to determine maximum plasma concentration (C-max), time to reach maximum concentration, half-life, total exposure to the drug, mean residence time, clearance rate per fraction absorbed, and absorption and elimination kinetic parameters. RESULTS C-max was reduced by 26% (P =.002), the absorption rate constant decreased 80% (P =.031), and the absorption half-life increased when Cerenia was administered diluted in LRS.