[Posture and circadian variations in serum theophylline concentrations].

We have reported that the morning mean rate of absorption (ka) in immediate release aminophylline tablet is significantly faster than the evening one without any obvious change in AUC, the distribution (Vd), the rate of elimination (kel) or the elimination half-time (t1/2) and this altered absorption is a cause of circadian variation of theophylline concentrations with sustained-release preparations. Now, we examined the effect of posture on theophylline absorption. Seven asthmatic children were given immediate release aminophylline tablets at the same time in the morning on two separate occasions. On one day they remained standing and on the other lying. Serum theophylline concentration was measured at 0, 0.5, 1, 2, 3, 4, 5 hours after dosing. Mean theophylline levels were higher in the standing position at all time and only the mean rate of absorption (ka) was significantly faster without any obvious change in parameters of pharmacokinetics. This result was almost consistent with differences of day and night theophylline kinetics. We conclude that slowness of absorption in the evening is mainly induced by difference in posture.