The present invention relates to a pharmaceutical composition adapted for oral administration, the composition comprising a pharmaceutical carrier and an organic arsenic compound, or its pharmaceutically acceptable salt, the compound having the structurewhereinR1 and R2 are independently alkyls with 1-10 carbon atomsX is S or SeR3 is -H, -COOH, -CH2-COOH, -CH2-CH2-COOH, -CH(CH3)-COOH, -CH(CH2-CH3)-COOH, or -CH2-CH2-CH2-COOHn is 0 or 1R4 is -OH, -H, -CH3, or a glutamine substituent orR3 and R4, together with C1 and C2, form an unsubstituted or substituted aromatic ring andR5 is -OH or a glycine substituent.
