Table 3.
Effect of probenecid on the different metabolic caffeine ratios commonly used for NAT2 phenotyping (a, b), and as indices of CYP1A2 (c), and XO (d) in 10 healthy fast and 10 slow acetylators
| AFMU/1MX(a) | P-value | AFMU/(AFMU +1MX + 1MU) (b) | P-value | (AFMU + 1MX +1MU)/17MU (c) | P-value | 1 MU/1MX(d) | P-value | |
|---|---|---|---|---|---|---|---|---|
| All volunteers (n = 30) | ||||||||
| Baseline value | 0.97 ± 0.21 | 0.24 ± 0.04 | 4.82 ± 0.33 | 1.34 ± 0.09 | ||||
| During probenecid | 1.53 ± 0.35 | < 0.002 | 0.26 ± 0.04 | 0.054 | 3.83 ± 0.37 | 0.25 | 2.24 ± 0.14 | < 0.0001 |
| 95% CI | 0.237, 0.876 | −0.0012, 0.0303 | −0.801, 0.309 | 0.74, 1.06 | ||||
| Fast acetylators (n = 15) | ||||||||
| Baseline value | 1.74 ± 0.21 | 0.40 ± 0.02 | 3.88 ± 1.33 | 1.52 ± 0.44 | ||||
| During probenecid | 2.73 ± 0.42 | < 0.004 | 0.42 ± 0.03 | 0.33 | 3.95 ± 1.58 | 0.77 | 2.52 ± 0.60 | < 0.002 |
| 95% CI | 0.47, 1.51 | −0.014, 0.046 | −0.644, 0.775 | 0.75, 1.26 | ||||
| Slow acetylators (n = 15) | ||||||||
| Baseline value | 0.21 ± 0.18 | 0.09 ± 0.08 | 4.28 ± 1.68 | 1.17 ± 0.31 | ||||
| During probenecid | 0.33 ± 0.04 | < 0.004 | 0.10 ± 0.01 | < 0.05 | 3.70 ± 1.83 | 0.19 | 1.96 ± 0.48 | < 0.002 |
| 95% CI | 0.063, 0.189 | 0.0007, 0.0250 | −1.40, 0.29 | 0.604, 0.189 |
Data are given as mean ±>s.e.m. with 95% CI on differences. AFMU, Acetyl-amino-6-formylamino-3-methyluracil; 1MX, 1-methylxanthine; 1MU, 1-methyuric acid.