Pharmacokinetics of multivesicular liposomal encapsulated cytarabine when administered subcutaneously in dogs

Abstract Background Prolonged cytotoxic concentrations of cytarabine (CA) are required for maximum cytotoxicity. DepoCyt is a human liposomal cytarabine (LC) product that lasts longer in plasma and CSF compared with free CA (FC). The use of LC has not been evaluated in dogs. Objectives To perform a LC pharmacokinetic (PK) study when administered SC in dogs. Animals Five healthy female beagles. Methods Three‐period, 3‐treatment, nonblinded, randomized, and crossover design, including a pilot study. LC was administered at 50 mg/m2 SC and FC was administered at 25 and 50 mg/m2 SC and IV. Plasma CA concentrations were measured until 240, 72, and 8 hours after SC LC, SC FC, and IV FC administration, respectively. CA plasma concentrations were quantitated by ultra‐high‐performance liquid chromatography with mass spectrometry (MS/MS) detection and concentration‐time profiles were evaluated by noncompartmental analysis. Results Subcutaneous LC administration resulted in a maximum plasma concentration of 26.3 to 59.78 ng/mL, time to reach maximum plasma concentration of 2 hours, area under the concentration‐time curve to last measurable concentration of 669.3 to 1126 h × ng/mL, and plasma bioavailability (%F) of 19.6% to 31.3%. The PK profiles of FC after SC and IV administration differed when compared with LC. Conclusions and Clinical Importance In healthy dogs, SC LC administration at 50 mg/m2 results in measurable plasma CA concentrations, is apparently safe and well tolerated, but does not result in prolonged cytotoxic plasma concentrations. Poor absorption of LC prevented establishment of a complete LC PK profile.