Pharmacokinetics of Caffeine following a Single Administration of Coffee Enema versus Oral Coffee Consumption in Healthy Male Subjects

Abstract

The objective of this study was to determine the pharmacokinetics of caffeine after single administration of a coffee enema versus coffee consumed orally in healthy male subjects. The study design was an open-label, randomized two-phase crossover study. Eleven healthy subjects were randomly assigned either to receive 500 mL of coffee enema for 10 minutes or to consume 180 mL of ready-to-drink coffee beverage. After a washout period of at least 10 days, all the subjects were switched to receive the alternate coffee procedure. Blood samples were collected immediately before and at specific time points until 12 hours after coffee administration in each phase. The mean caffeine content in both the coffee solution prepared for the coffee enema and the ready-to-drink coffee beverage was not statistically different. The C max and AUC of caffeine obtained from the coffee enema were about 3.5 times significantly less than those of the coffee consumed orally, despite having slightly but statistically faster T max. The t 1/2 of caffeine obtained following both coffee procedures did not statistically differ. In summary, the relative bioavailability of caffeine obtained from the coffee enema was about 3.5 times significantly less than those of the coffee consumed orally.

Figure 1

Chromatogram of plasma sample containing 4.00 μg/mL of internal standard (IS, retention time = 4.217 min) and 4.00 μg/mL of caffeine (retention time = 7.082 min).

Figure 2

Mean plasma caffeine concentration-time curves following a single administration of the coffee enema (CE) or the oral coffee consumption (CC) (n = 11). *Statistically significant between groups (P < 0.05, paired t-test).