Dyphylline is 7-(2,3-dihydroxypropyl)-theophylline, a white, extremely bitter, amorphous powder that is freely soluble in water and soluble in alcohol. Dyphylline is stable in gastrointestinal fluids over a wide range of pH. Dyphylline is a xanthine derivative with pharmacologic actions similar to theophylline and other members of this class of drugs. Its primary action is that of bronchodilation, but it also exhibits peripheral vasodilatory and other smooth muscle relaxant activity to a lesser degree. The bronchodilatory action of dyphylline, as with other xanthines, is thought to be mediated through competitive inhibition of phosphodiesterase with a resulting increase in cyclic AMP producing relaxation of the bronchial smooth muscle. Dyphylline exerts its bronchodilatory effects directly and, unlike theophylline, is excreted unchanged by the kidneys without being metabolized by the liver. Because of this, dyphylline pharmacokinetics and plasma levels are not influenced by various factors that affect liver function and hepatic enzyme activity, such as smoking, age, congestive heart failure, or concomitant use of drugs which affect liver function.

Proxyphylline is a xanthine derivative that acts as a cardiac stimulant, vasodilator and bronchodilator. In combination with ephedrine it’s used for relief of acute bronchial asthma and for reversible bronchospasm associated with chronic bronchitis and emphysema. Proxyphylline is readily absorbed from the gastrointestinal tract and it’s not converted to theophylline in the body. The clinical studies are agreed with the property of proxyphylline to inhibit the cyclic nucleotide phosphodiesterases.

Etofylline [7-(2-hydroxyethyl)theophylline] is a N-7-substituted derivative of theophylline, a smooth muscle relaxant. Etofylline is used to relieve bronchoconstriction. It may act as a phosphodiesterase inhibitor and adenosine receptor antagonist.