“…Theophylline (1,3-dimethyl-7H-purine-2,6-dione, or 1,3-dimethylxanthine, Figure ) is used in treatment of acute asthma, tremor therapy, and as a diuretic, although it is limited , by its low solubility and conversion between anhydrous and monohydrate forms. The low water solubility of theophylline can be improved by the addition of acid or base “guest” molecules − to form a complex (salt or co-crystal), as theophylline is amphoteric. Formation of co-crystals and salts has also been studied in order to improve the stability of anhydrous theophylline on exposure to elevated relative humidity (RH), , as interconversion between the anhydrous and monohydrate forms are known to occur as a function of RH .…”