*3.1. Pharmacokinetics of Tofacitinib after Intravenous and Oral Administration to Rats*

Figure 2A shows the mean arterial plasma concentration-time profiles after intravenous infusion of 5, 10, 20, and 50 mg/kg tofacitinib over 1 min, and Table 1 shows the associated pharmacokinetic parameters. At all four doses, the mean arterial plasma concentrations of tofacitinib showed a polyexponential decrease. The dose-normalized AUCs following intravenous infusion of 5, 10, 20, and 50 mg/kg tofacitinib were 282, 342, 404, and 705 µg·min/mL, respectively (Table 1 and Supplementary Figure S1A). The dose-normalized AUC at 50 mg/kg was 2.50-, 2.06-, and 1.75-fold greater than the dose-normalized AUCs at 5, 10, and 20 mg/kg, respectively (*p* < 0.001 each). CL and CLNR at 50 mg/kg were significantly slower than at 5, 10, and 20 mg/kg (*p* < 0.01 each). Thus, the terminal half-life and MRT were significantly longer following infusion of 50 mg/kg tofacitinib than the other doses (*p* < 0.001 each), whereas *V*ss and the percentage of intravenous tofacitinib excreted unchanged in 24-h urine (*Ae*0–24 h) did not differ significantly among the four intravenous doses (Table 1). The CL<sup>R</sup> was 69%, 71%, and 71% slower at 50 mg/kg than at 5, 10, and 20 mg/kg, respectively, because the *Ae*0–24 h was smaller and AUC was greater at 50 mg/kg than at the other doses. However, the percentages of tofacitinib recovered unchanged from the entire gastrointestinal tract (including its contents and feces) at 24 h (GI24 h) were negligible for all four intravenous doses (data not shown). Taken together, these findings indicate that the pharmacokinetic parameters of intravenous tofacitinib in rats were dependent on dose.

**Figure 2.** Mean arterial plasma concentration-time profiles of tofacitinib in Sprague-Dawley rats after (**A**) 1-min intravenous infusion of 5 (*n* = 9), 10 (*n* = 8), 20 (*n* = 7), and 50 (*n* = 7) mg/kg tofacitinib and (**B**) oral administration of 10 (*n* = 7), 20 (*n* = 8), 50 (*n* = 9), and 100 (*n* = 7) mg/kg tofacitinib. Bars represent standard deviations (SD).

**Table 1.** Pharmacokinetic parameters of tofacitinib after 1-min intravenous infusion of the drug at various doses to male Sprague-Dawley rats. Data are expressed as mean ± standard deviation (SD).


AUC values were normalized to tofacitinib dose of 10 mg/kg for statistical analysis. <sup>a</sup> 20 mg/kg was significantly different (*p* < 0.05) from 5 mg/kg. 50 mg/kg was significantly different (*p* < 0.001) from 5, 10 and 20 mg/kg. <sup>b</sup> 50 mg/kg was significantly different (*p* < 0.001) from 5, 10 and 20 mg/kg. <sup>c</sup> 5 mg/kg was significantly different from 10 (*p* < 0.05) and 20 (*p* < 0.001) mg/kg, respectively. 50 mg/kg was significantly different (*p* < 0.001) from 5, 10 and 20 mg/kg. <sup>d</sup> 5 mg/kg was significantly different from 10 (*p* < 0.05), 20 (*p* < 0.01) and 50 (*p* < 0.001) mg/kg, respectively. 50 mg/kg was significantly different from 10 (*p* < 0.001) and 20 (*p* < 0.01) mg/kg, respectively.

Figure 2B shows the mean arterial plasma concentration-time profiles following oral administration of 10, 20, 50, and 100 mg/kg tofacitinib, and Table 2 shows the associated pharmacokinetic parameters. Orally administered tofacitinib, at all four doses, was rapidly absorbed by the rat gastrointestinal tract, with tofacitinib detected in plasma within 5 min. After reaching *T*max, the plasma concentrations of tofacitinib showed a polyexponential decrease for all four doses. The dose-normalized AUCs following oral administration of 10, 20, 50, and 100 mg/kg tofacitinib were dose dependent, being 99.4, 135, 238, and 407 µg·min/mL, respectively (Table 2 and Supplementary Figure S1B). The dose-normalized AUC at 100 mg/kg was 4.09-, 3.01-, and 1.71-fold greater than those at 10, 20, and 50 mg/kg, respectively (*p* < 0.01 each). The CL<sup>R</sup> was much slower at 100 mg/kg than at the other doses because AUC was significantly greater at 100 mg/kg. *T*max was significantly longer at 100 mg/kg than at 10, 20 and 50 mg/kg (*p* < 0.05 each). The dose-normalized *C*max (based on 10 mg/kg dose), GI24 h, and *Ae*0–24 h did not differ significantly among the four oral doses studied (Table 2). Based on the AUC of 10 mg/kg intravenous tofacitinib, the *F* values for oral doses of 10, 20, 50, and 100 mg/kg were 29.1%, 39.3%, 69.7%, and 119%, respectively. These findings indicated that the pharmacokinetic parameters of orally administered tofacitinib in rats were dependent on dose.


**Table 2.** Pharmacokinetic parameters of tofacitinib after oral administration of the drug at various doses to male Sprague-Dawley rats.

Data are expressed as mean ± standard deviation (SD). AUC and *C*max values were normalized to tofacitinib dose of 10 mg/kg for statistical analysis. *F* was calculated by dose-normalized AUC (based on 10 mg/kg) after oral administration of tofacitinib divided by AUC after intravenous administration of the drug at dose of 10 mg/kg. <sup>a</sup> 10 mg/kg was significantly different (*p* < 0.05) from 50 mg/kg. 100 mg/kg was significantly different from 10 (*p* < 0.001), 20 (*p* < 0.001) and 50 (*p* < 0.01) mg/kg, respectively. <sup>b</sup> 100 mg/kg was significantly different (*p* < 0.05) from 10, 20 and 50 mg/kg. <sup>c</sup> 10 mg/kg was significantly different from 20 (*p* < 0.05) and 100 (*p* < 0.001) mg/kg, respectively.
