TABLE 2

Known influence of PCPs on compound interactions with cells, membranes, and transporters

An upward arrow indicates positive correlation, and a downward arrow indicates negative correlation.

PCP	Membrane Permeability	Caco-2 Permeability	P-gp Substrate^{^a}	P-gp Nonsubstrate^{^a}
MW	↓^{^b}		>400^{^c}	<400^{^c}
ONC			≥8^{^c}	≤4^{^c}
logD_7.4		↑^{^d}
logP	↑^{^b}
Acidic pK_a			<4^{^c}
Basic pK_a				<8^{^c}
IP	↓^{^b}
PSA	↑^{^b}	↓^{^d}

MW, molecular weight; ONC, O + N atom count; logP, log of the partition coefficient; logD_7.4, log of the distribution coefficient at pH = 7.4; IP, ionization potential; PSA, polar van der Waals' surface area.
a Rule of fours (Didziapetris et al., 2003).
b McGinnity et al., 2004.
c Didziapetris et al., 2003.
d Artursson et al., 2001.