DMPK

IVIVE: Predicting Human Clearance from In Vitro Data

Pharazi.ai TeamMarch 10, 20268 min read

What Is IVIVE in Drug Discovery?

In vitro–in vivo extrapolation (IVIVE) is the foundational quantitative method for predicting human pharmacokinetic parameters from in vitro metabolic stability experiments.

IVIVE serves as a critical translational bridge in early DMPK screening, enabling human PK projections long before First-In-Human (FIH) trials.

The standard IVIVE workflow proceeds in three core steps:

Measure In Vitro Intrinsic Clearance

The most common assay is the substrate depletion approach in Human Liver Microsomes (HLM):

C L_{in t, e x t mi c} = \frac{0.693}{t _{1/2, e x t mi c}} im es \frac{V _{e x t in c u ba t i o n}}{P _{e x t p r o t e in}}

Where:

$t_{1/2, e x t mi c}$ = in vitro half-life from substrate depletion slope (min)
$V_{e x t in c u ba t i o n}$ = total incubation volume (µL)
$P_{e x t p r o t e in}$ = total microsomal protein mass (mg)

Apply Physiological Scaling Factors

Scale in vitro

C L_{in t}

to whole-liver intrinsic clearance:

C L_{in t, e x t l i v er} = C L_{in t, e x t mi c} im es M P P G L im ese x t L i v er W e i g h t

Scaling Factor	Value	Source
MPPGL	~40 mg/g	Healthy human adults
Liver Weight	1500 g	70 kg human (~21.4 g/kg)
HPGL (hepatocytes)	120 × 10⁶ cells/g	Alternative system

Apply the Well-Stirred Liver Model

C L_{H} = \frac{Q _{H} \cdot f _{u} \cdot C L _{in t, e x t l i v er}}{Q _{H} + f _{u} \cdot C L _{in t, e x t l i v er}}

Where:

$Q_{H}$ = Hepatic blood flow (~1450 mL/min for 70 kg)
$f_{u}$ = Fraction unbound in plasma

When

f_{u} \cdot C L_{in t} ≪ Q_{H}

C L_{H} \approx f_{u} \cdot C L_{in t}

Clearance is restricted by enzymatic capacity.

When

f_{u} \cdot C L_{in t} ≫ Q_{H}

C L_{H} \approx Q_{H}

Clearance approaches blood delivery speed.

The fu,mic Correction

Neglecting the fu,mic correction is the #1 cause of under-prediction of in vivo clearance for lipophilic drug candidates.

C L_{in t, u} = \frac{C L _{in t, e x t mi c}}{f _{u, e x t mi c}}

If not measured experimentally, the Austin–Barton equation estimates it:

lo g (\frac{1}{f _{u, e x t mi c}} - 1) = 0.072 im es lo g P + 0.067 im es [e x t p r o t e in] - 1.126

Worked IVIVE Example

Given:

t_{1/2, e x t mi c} = 25 e x t min

at 0.5 mg/mL HLM,

f_{u} = 0.05

f_{u, e x t mi c} = 0.8

Base CL_int

C L_{in t, e x t mi c} = \frac{0.693}{25} im es \frac{1}{0.5} = 0.0554 e x t m L / min / m g

Corrected & Scaled

C L_{in t, u} = \frac{0.0554}{0.8} = 0.0693 e x t m L / min / m g

C L_{in t, e x t l i v er} = 0.0693 im es 40 im es 1500 = 4158 e x t m L / min

Hepatic Clearance

C L_{H} = \frac{1450 im es 0.05 im es 4158}{1450 + 0.05 im es 4158} = 181.7 e x t m L / min

Extraction ratio:

E_{H} = 181.7/1450 = 0.125

(low-to-moderate).

Common Pitfalls

Watch out for these frequent IVIVE translation errors.

Ignoring extrahepatic metabolism — IVIVE only predicts hepatic metabolism
Incorrect scaling vectors — Adult MPPGL values fail for pediatric populations
Transporter limitations — Active uptake drugs (statins, OATP substrates) break standard models

Try It on Pharazi.ai

Use the IVIVE Hepatic Clearance Calculator or the fu,mic Correction Calculator.

References

Obach RS. Drug Metab Dispos. 1999;27:1350–1359.
Austin RP, Barton P, et al. Drug Metab Dispos. 2002;30:1497–1503.

IVIVEclearancemicrosomeshepatocyteswell-stirred modelDMPKfu,mic