Quercetin Significantly Inhibits the Metabolism of Caffeine, a Substrate of Cytochrome P450 1A2 Unrelated to   (−2964G>A) and (734C>A) Gene Polymorphisms

Table 1

Pharmacokinetic parameters of caffeine and its metabolite paraxanthine (17X) and the relationship with CYP1A2 genotype in 12 healthy subjects before and after the 14-day quercetin treatment.

Parameters	CYP1A2*1C/*1F (GG/AA, 𝑛=6)						CYP1A2*1C/*1F (GA/CA, 𝑛=6)
	Caffeine			17X			Caffeine			17X
	Before	After	Ratio	Before	After	Ratio	Before	After	Ratio	Before	After	Ratio
𝐶max (𝜇mol/L)	19.8 (13.6, 30.0)	18.3 (14.2, 22.3)	1.2 (0.7, 1.6)	6.6 (5.4, 7.8)	5.3 (4.7, 5.8)	1.2 (1.0, 1.4)	16.6 (12.6, 20.5)	20.4 (12.8, 28.1)	0.9 (0.7, 1.0)	6.6 (5.7, 7.5)	5.8 (4.5, 7.1)	1.2 (0.8, 1.7)
AUC(0--24h) (𝜇mol/L·h)	85.1 (66.8, 103.4)	77.6 (55.4, 99.9)	1.0 (0.8, 1.1)	112.4 (90.8, 134.0)	89.6 (73.8, 105.4)	1.3 (1.1, 1.4)*	121.9 (81.4, 162.4)	122.0 (93.6, 150.5)	1.2 (0.8, 1.6)	91.5 (77.8, 105.3)	77.9 (61.0, 94.7)	1.3 (1.1, 1.9)*
𝑇max (h)	1.5 (0.5, 2.0)	1.0 (0.5, 1.5)	NA	9 (2, 12)	6 (3, 12)	NA	1.0 (0.5, 2.5)	1.5 (0.9, 3.0)	NA	5.0 (3.0, 6.0)	6.0 (2.0, 10)	NA
𝑡1/2 (h)	4.5 (3.4, 6.7)	4.5 (3.4, 6.6)	1.2 (0.7, 1.7)	6.6 (4.9, 8.4)	8.0 (6.7, 9.2)	0.8 (0.7, 1.0)	4.1 (3.6, 4.5)	4.1 (3.5, 4.7)	1.1 (1.0, 1.3)	4.9 (4.1, 5.7)	5.4 (4.8, 5.9)	0.9 (0.8, 1.1)

𝐶_max, maximum concentration; 𝑇_max, time to maximum concentration; AUC_(0--24), area under concentration-time curve extrapolated to 24 h; NA, not applicable; CI, confidence interval. The 90% CI of the ratio of logarithmically transformed parameters was calculated as before quercetin versus after quercetin treatment. AUC_(0--24h) value of caffeine in the CYP1A2*1C/*1F (GG/AA) group was much lower than in the CYP1A2*1C/*1F (GA/CA) group. ^∗𝑃<0.05 for comparison for 137 and 17X groups between the phases before and after quercetin treatment.