Abstract: The invention relates to novel clathrate complexes of cyclodextrin or arabinogalactan with 9-phenyl-sym-octahydroselenoxanthene, possibly in ?-crystalline form, The clathrate complex may be in crystalline form, possibly in the form of nano-particles. In the clathrate complex, cyclodextrin is selected from ?-, ?-, ?- or hydroxypropyl-?-cyclodextrin, primarily ?-cyclodextrin. The proposed clathrate complexes make it possible to increase the water-solubility of the active compound, to improve the bioavailability, to reduce the dosage of the drug and, consequently, to reduce the toxic effect of 9-phenyl-sym-octahydroselenoxanthene. The complexes exhibit cytoradioprotective activity. The invention also relates to a liquid-phase and solid-phase methods for producing clathrate complexes, as well as to pharmaceutical compositions and drugs thereof.