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Is this compound likely to be absorbed from the gut?

Caco-2 permeability (Papp) calculator

Calculates how fast a compound crosses a monolayer of intestinal Caco-2 cells grown on a membrane (Papp), and whether the cells pump it back out (efflux ratio).

When to use itUse it when screening oral candidates, to check from raw assay data whether a compound is likely to be absorbed and whether efflux pumps such as P-gp push it back.

Prefilled with an example: a 12-well insert (1.12 cm²) with 120 pmol crossing in 2 hours. Change any value and the result updates.

pmol/s

How fast the amount in the receiver compartment grows, per second. Take it from the stretch where the amount rises linearly with time. Divide a per-minute value by 60.

cm²

About 1.12 cm² for a 12-well insert and about 0.33 cm² for a 24-well insert.

pmol/mL

The concentration on the dosing (donor) side at the start. 10 µM is 10,000 pmol/mL.

×10⁻⁶ cm/s

For the efflux ratio. Enter the value measured from the blood side toward the gut lumen.

×10⁻⁶ cm/s

For the efflux ratio. Enter the value measured from the gut lumen toward the blood side (the absorptive direction).

Permeability (Papp)1.491 ×10⁻⁶ cm/s
Efflux ratio4

The compound crosses the monolayer readily. In the Artursson 1991 system, this is the range of drugs almost completely absorbed in humans. The efflux ratio is 4, so a pump may be moving it back out. Confirm with an inhibitor. Cutoffs differ between labs, so judge it against reference drugs on the same plate.

How to read it (values from the Artursson 1991 system; cutoffs vary by lab)

The row that matches your result is marked.

  • Papp below 0.1 (×10⁻⁶ cm/s)Range of poorly absorbed drugsIn Artursson 1991, drugs with under 1% absorption in humans had a Papp of 0.1 or less. The cutoffs shift with each lab's system, so judge against reference drugs run on the same plate.
  • Papp 0.1 to 1Range of partly absorbed drugsIn the same report, drugs absorbed above 1% and below 100% fell in this range. Do not call high or low from the number alone; rank it against reference drugs such as the low-permeability atenolol.
  • Papp above 1Your resultRange of almost completely absorbed drugsIn the same report, drugs almost completely absorbed in humans had a Papp above 1. Values move a lot with conditions such as stirring, though, so you cannot compare them directly with another lab's numbers.
  • Efflux ratio below 2No notable effluxLittle sign that pumps such as P-gp are pushing the compound back.
  • Efflux ratio of 2 or moreYour resultPossible active effluxUnder ICH M12, a compound is considered a substrate of the transporter (P-gp, for example) if the efflux ratio is 2 or more and a known inhibitor lowers it by more than 50%.

How it is calculated

The first three fields give Papp (shown in ×10⁻⁶ cm/s), and the last two give the efflux ratio. Both assume data from monolayers confirmed to be intact by TEER (the electrical resistance across the layer) or Lucifer yellow permeability.

Papp (cm/s) = (dQ/dt) ÷ (A × C0) efflux ratio = Papp(B→A) ÷ Papp(A→B)

Source: The apparent permeability Papp = (dQ/dt) ÷ (A × C0) is the standard Caco-2 equation, in use since Artursson P and Karlsson J (1991). The efflux-ratio criterion for transporter substrates follows ICH M12 (2024).

With your numbers

  1. Papp = (dQ/dt) ÷ (A × C0) = 0.0167 ÷ (1.12 × 10,000) = 1.491 ×10⁻⁶ cm/s
  2. efflux ratio = Papp(B→A) ÷ Papp(A→B) = 6 ÷ 1.5 = 4

Limits of this calculation

  • No Papp cutoff for high or low holds in every lab. The guide values above (0.1 and 1 ×10⁻⁶ cm/s) come from one lab's system, in which Artursson and Karlsson compared 20 drugs with their absorption in humans in 1991.
  • Values also move with stirring, insert type, days in culture, passage number and buffer pH. Judge high or low by ranking against reference drugs on the same plate, such as high-permeability metoprolol and low-permeability atenolol.
  • The efflux ratio of 2 is the ICH M12 criterion and goes together with checking whether an inhibitor lowers the ratio by more than 50%. Another cutoff can be used if your system's track record justifies it.
  • Data from monolayers that failed quality checks such as TEER or Lucifer yellow cannot be used.
  • If the units of dQ/dt, C0 and area do not match, the result is off by orders of magnitude. Entering dQ/dt per minute makes Papp 60 times too high. Treat the result as an estimate for learning.

Primary sources

Every calculator gives an estimate for learning, built on published information and primary sources. Real decisions follow the applicable guidance and expert judgment.