Interaction of theophylline and phenobarbital in solution

Abstract

In aqueous solution theophylline (T) and phenobarbital (P) form a weak 2:1 complex. The van't Hoff factor is about 2.5. Although diffusion measurements show that two T and one P molecules pass through a membrane together as a unit, the moieties evidently have a high degree of independent translation relative to one another. This long range interaction in solution is indicated not be be coulombic but to probably involve hydrogen bonding weakened by the presence of solvent molecules and ions. Thus P and T used together in biological systems may affect each other's bioavailability.