Table 4.
Pharmacokinetics of caffeine when described as caffeine or placebo.
| Untransformed | Log-transformed | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| AUC14 (μg/ml*hr) | AUC∞ (μg/ml*hr) |
Cmax (μg/ml) |
Tmax (hr) |
t 1/2 (hr) |
AUC14 (μg/ml*hr) |
AUC∞ (μg/ml*hr) |
Cmax (μg/ml) |
t 1/2 (hr) |
|
| Described as Caffeine* | 58.4 (4.6) | 82.8 (9.6) | 7.2 (0.5) | 2.9 (0.3) | 6.3 (0.5) | 4.01 (0.08) | 4.30 (0.10) | 1.93 (0.07) | 1.77 (0.08) |
| Described as Placebo* | 56.2 (4.3) | 77.4 (8.7) | 7.1 (0.4) | 2.7 (0.2) | 5.92 (0.5) | 3.97 (0.07) | 4.24 (0.10) | 1.93 (0.06) | 1.71 (0.08) |
| ANOVA† | 2.33 [0.35 to 4.31] P = 0.02 |
5.43 [1.62 to 9.23] P = 0.008 |
0.06 [-0.25 to 0.37] P = 0.70 |
0.22 [-0.33 to 0.77] P = 0.42 |
0.40 [0.12 to 0.68] p = 0.007 |
1.04 [1.00 to 1.07] P = 0.05 |
1.07 [1.02 to 1.11] P = 0.004 |
1.00 [0.94 to 1.06] P = 0.99 |
1.07 [1.02 to 1.12] P = 0.01 |
| Wilcoxon Signed Ranks‡ | P = 0.02 | P = 0.006 | P = 0.61 | P = 0.46 | P = 0.007 | ||||
*Data are unadjusted mean (SE) before and after natural logarithmic transformation. †Data are adjusted point estimate [95% confidence interval]. Point estimate is "receivng caffeine described as caffeine" mean - "receivng caffeine described as placebo" mean (untransformed data) or ratio of their geometric means (transformed data). The ANOVA model included group, subjects nested in groups, period, and intervention. There was no significant period or group effects (P = 0.45 to 0.80). ‡Comparing "receiving caffeine described as caffeine" to "receiving caffeine described as placebo". AUC14, area under the plasma concentration-time curve from time 0 to 14 hour (calculated by linear trapezoidal method); AUC∞, area under the plasma concentration-time curve from time 0 to infinity (AUC4 + last measured level/terminal rate constant); Cmax and Tmax, maximum measured plasma level and its time; t1/2, plasma half-life (Ln 2/terminal elimination constant [slope of the linear regression line of natural log-transformed last 6 measurable caffeine levels vs time curve]).