Simple SummaryThis study aimed to evaluate the rate and amount of cyclosporine A in cats following oral administration using intravenous administration as a reference. Twenty-four healthy cats were selected and randomly divided into four groups in this study. All animals were adapted in a convenient environment during the whole experiment and no adverse effect was observed. Each animal was given a respective dose only once. Blood samples were collected at scheduled time points and analyzed by the established method. The pharmacokinetic parameters were calculated by professional software used in the whole pharma industry of drug development. As a result, the amount of cyclosporine A absorbed in vivo is from one-fifth to one-third, demonstrating that the medium dose has great potential to get into the body. Due to its common side effects always being associated with the amount of cyclosporine in the blood, it is necessary to monitor the concentration of cyclosporine clinically. Practically, doctors draw blood before or 2 h after taking medicine. In this study, we concluded that taking a blood sample after 4 h has more power to estimate the extent of absorption and will be better at preventing the occurrence of side effects in clinical use.AbstractThis study aimed to evaluate the absolute bioavailability of cyclosporine in cats by investigating the pharmacokinetic profile after intravenous and oral administration, respectively. Twenty-four clinically healthy cats were enrolled in this study and randomly divided into four groups, namely the intravenous group (3 mg/kg), low oral group (3.5 mg/kg), medium oral group (7 mg/kg), and high oral group (14 mg/kg). Whole blood was obtained at the scheduled time points after a single dose administration and cyclosporine was determined using ultra-performance liquid chromatography–tandem mass spectrometry technology (UPLC-MS/MS). Pharmacokinetic parameters were calculated using the WinNonlin 8.3.4 software via compartmental and non-compartmental models. As a result, the bioavailability values for the low, medium, and high oral groups were 14.64%, 36.98%, and 13.53%, respectively. The nonlinear pharmacokinetic profile was observed in the range from 3.5 mg/kg to 14 mg/kg in cats following oral administration. Whole blood concentrations taken 4 h after oral administration were better correlated with the area under the blood concentration–time curve AUC0–24with a high regression coefficient (R2= 0.896). This concentration would be a greater predictor in the following therapeutic drug monitoring. No adverse effect was observed in the whole study process.