Plasma concentrations of mirtazapine are significantly different between sampling sites after oral administration in...

To evaluate the pharmacokinetics of mirtazapine (MRZ) after single-dose oral administration in healthy adult alpacas and compare concentrations at 2 venous sampling sites.

This study was conducted during the weeks of January 29, 2024, and February 15, 2024. A single dose of 2 mg/kg MRZ was administered orally via syringe to 7 healthy adult alpacas. Blood was collected from jugular vein (JV; n = 7) and cephalic vein (CV; 5) catheters immediately prior to and at predetermined times for 24 hours after administration. Plasma MRZ concentrations were determined by UPLC-MS-MS. Pharmacokinetic parameters were determined for each sampling site, and statistical analysis was performed by paired t tests.

Mean maximum plasma concentrations (Cmax) from JV samples (183 ± 95.2 ng/mL) occurred at time 0.0281 ± 0.029 hours and were significantly higher than CV samples' Cmax (4.84 ± 2.37 ng/mL), which occurred at time 0.464 ± 0.093 hours. Comparison of dose-corrected Cmax and area under the concentration-time curve from time zero extrapolated to infinity with those previously reported show the Cmax from JV samples in alpacas is similar to cats (166 ng/mL), but the Cmax from the CV samples failed to reach that reported in dogs (140 ng/mL) and people (123 ng/mL).

Plasma concentrations of MRZ were significantly different between sampling sites, resulting in different interpretations for potential use in alpacas.

Additional information is needed before using oral MRZ in alpacas, including studies of different doses, formulations, or routes of administration.