*2.8. Calculation of F<sup>a</sup>* × *F<sup>g</sup> in Human*

The first-pass GI availability (*F<sup>a</sup>* × *Fg*) of selected drugs was calculated using the equation:

$$F\_a \times F\_{\mathcal{g}} = F / F\_{\mathcal{h}}$$

where *F* is the total oral availability, *F<sup>a</sup>* the fraction absorbed, *F<sup>g</sup>* the intestinal availability and *F<sup>h</sup>* the hepatic availability. The hepatic availability *F<sup>g</sup>* can be estimated with the equation:

$$F\_{\mathcal{S}} = 1 - \mathbb{C}L\_{\mathbb{H}} / Q\_H$$

where *CL<sup>h</sup>* is the hepatic clearance of a drug and *Q<sup>H</sup>* the hepatic blood flow in human (20.7 mL/min/kg). The hepatic clearance *CL<sup>h</sup>* is calculated with the equation:

$$\mathbf{CL}\_{h} = \mathbf{CL}\_{b} \times (1 - f\_{e})$$

where *CL<sup>b</sup>* is the blood clearance of a drug and *f<sup>e</sup>* the fraction of renal excretion. Blood *CL<sup>b</sup>* can be converted from plasma clearance *CL<sup>p</sup>* with the blood-to-plasma ratio *RB*:

$$\mathcal{C}\mathcal{L}\_b = \mathcal{C}\mathcal{L}\_p/\mathcal{R}\_B$$

A set of 12 marketed drugs are selected for the evaluation of EpiIntestinal microtissues. The clinical data for the calculation of *F<sup>a</sup>* × *F<sup>g</sup>* are summarized in Table 2.

**Table 2.** Clinical pharmacokinetic data of the selected drugs for the calculation of *F<sup>a</sup>* × *Fg*. Data sources are indicated. Due to a lack of literature data or conflicting data in the literature, R<sup>B</sup> values for several compounds are measured in-house (#).


\* Prescription information at fda.gov.
