Table 1

Effects of loratadine, desloratadine, and 3-OH-desloratadine on CYP activities in human hepatic microsomes

	Cytochrome P-450, Percentage of Control
	CYP3A4	CYP3A4	CYP1A2	CYP2C19	CYP2C9	CYP2D6
10 μM LOR	118.6	86.9	99.4	26.4	68.7	45.1
IC₅₀LOR	≥10 μM	≥10 μM	≥10 μM	≅0.76 μM	≥10 μM	≅8.1 μM
10 μM DL	84.0	80.0	110.4	112.5	106.3	86.3
IC₅₀DL	≥10 μM	≥10 μM	≥10 μM	≥10 μM	≥10 μM	≥10 μM
10 μM 3-OH-DL	75.3	90.0	98.2	101.4	89.5	97.9
IC₅₀3-OH-DL	≥10 μM	≥10 μM	≥10 μM	≥10 μM	≥10 μM	≥10 μM
Substrate	dextromethorphan	testosterone	7-ethoxyresorufin	mephenytoin	diclofenac	dextromethorphan

The IC₅₀ experiments were run at approximateK_m values established in our laboratory for pooled human liver microsomes and, in general, correspond withK_m values found in the literature: [3A4-dextromethorphan] Schmider et al., 1997; [3A4-testosterone]Wang et al., 1997; [1A2] Lin et al., 2001; [2C19] Easterbrook et al., 2001; [2C9] Tang et al., 2000; [2D6] Hickman et al., 1998.