Caffeine pharmacokinetics during hyperbaric hyperoxia in humans

The effect of hyperbaric hyperoxia on the pharmacokinetics of caffeine was investigated in human volunteers. Some 600 ml of coffee were administered to 2 volunteers and blood samples were serially collected for 24 h. The volunteers entered a hyperbaric chamber 2.5 h following coffee ingestion for a total period of 110 min (0.25 MPa, alternating 100% O2-breathing for 20 min and air breathing for 5 min). The concentrations of caffeine in serum was determined by high pressure liquid chromatography. The caffeine amount ingested was determined by analyzing an aliquot of the coffee beverage. Data were analyzed assuming linear kinetics and an open one-compartment model. Effects of hyperbaric hyperoxia on caffeine disposition were investigated using a runs test. Moreover, a one-population t-test was applied to residuals, separately for data from the initial normobaric period, the hyperbaric period and the terminal normobaric period. Pharmacokinetic parameters were similar to established literature data on caffeine [Volunteer 1: maximal concentration (Cmax: 6.13 mg.L-1 at Tmax: 55 min, half-time of elimination (T1/2: 180 min, total clearance (Cl): 3.41 ml.min-1.kg-1; volume of distribution (Vd: 0.88 I.kg-1; Volunteer 2: Cmax: 6.23 mg.L-1, Tmax: 94 min, T1/2: 283 min, Cl: 1.90 ml.min-1.kg-1, Vd: 0.77 L.kg-1). The runs test as well as the analysis of residuals gave no evidence for alterations of caffeine disposition by hyperoxia (p > 0.05). The pharmacokinetics of caffeine do not seem to be influenced in a clinically relevant way in humans during a stay for 100 min at 0.25 MPa, alternating 100% O2 and air breathing.