Table 3.

Correlation of sildenafil N-demethylation and CYP activities (using log data for both).

	Correlation coefficient (r)
Isoform (substrate)	2.5 µm sildenafil	250 µm sildenafil
CYP1A2 (caffeine)	0.49 (n = 10)	0.53 (n = 10)
CYP2A6 (coumarin)	0.24 (n = 12)	0.44 (n = 12)
CYP2C9 (phenytoin)	0.77* (n = 14)	0.80** (n = 14)
CYP2C19 (S-mephenytoin)	0.48 (n = 10)	0.31 (n = 10)
CYP2D6 (bufuralol)	0.34 (n = 14)	0.33 (n = 14)
CYP2E1 (chlorzoxazone)	0.36 (n = 14)	0.49 (n = 14)
CYP3A4 (testosterone)	0.87** (n = 14)	0.84** (n = 14)

^*P < 0.01

^**P < 0.001. All other correlations were not statistically significant. n = number of human livers