Theophylline is structurally related to theobromine and caffeine. The precise mechanism of action of theophylline is not known, however, it is thought to be a phosphodiesterase inhibitor which may give a bronchodilatory effect. It also binds adenosine receptors.
Aminophylline is the ethylenediamine salt of theophylline. Theophylline stimulates the CNS, skeletal muscles, and cardiac muscle. It relaxes certain smooth muscles in the bronchi through PDE3 inhibition, produces diuresis, and causes an increase in gastric secretion.