A composition and method for the treatment of the side-effects associated with the administration of cancer chemotherapeutic agents involves the oral ingestion of a slow release capsule containing adenine and orotate. The administration of a protein pump inhibitor decreases systemic absorption of orotate and the administration of allopurinol decreases the formation of 2,8-dihydroxy adenine from adenine. In an alternative embodiment, cationic liposomes contain purine/pyrimidine precursors. The cationic liposomes bind to the cells lining the mucosa of the intestinal tract and then the contents of the cationic liposome are then taken up in the interior of the cells to prevent the metabolism of the cancer treatment drug 5-FU into a toxic species.