Pharmacokinetic comparison of a slow-release theophylline-hydroxyzine combination and a plain slow-release theophylline preparation.

We have compared the pharmacokinetic properties of a slow-release theophylline-hydroxyzine combination and a slow-release theophylline preparation both after a single dose administration and at steady state after the dosage of twice/day for four days in ten healthy volunteers. After a single dose, theophylline was absorbed slightly faster from the combination preparation (Retafyllin comp.) than from a plain theophylline preparation (Theo-Dur). However, in a steady state phase the pharmacokinetic profiles were quite similar. Hydroxyzine showed a slight delay in absorption from the combination preparation, but in a steady state the overall pharmacokinetic profile of hydroxyzine was similar to that of theophylline. Cumulation of either hydroxyzine or theophylline was not evident. On the basis of the present study, the slow-release combination preparation of theophylline and hydroxyzine seems suitable for twice/day dosage.