Ans. D: Busulfan Incidence of thrombocytopenia is higher with use of Busulfan. Prolonged administration may cause amenorrhoea, wasting, pigmentation, gynaecomastia, anhydrosis and pulmonary fibrosis. Busulfan Busulfan is a cell cycle non-specific alkylating antineoplastic agent, in the class of alkyl sulfonates. Its chemical designation is 1,4-butanediol dimethanesulfonate. Currently, its main uses are in bone marrow transplantation, especially in chronic myelogenous leukemia (CML), where it is used as a conditioning drug. Its mechanism of action through alkylation produces guanine-adenine intrastrand crosslinks. This occurs through an SN2 reaction in which the relatively nucleophilic guanine N7 attacks the carbon adjacent to the mesylate leaving group. This kind of damage cannot be repaired by cellular machinery and thus the cell undergoes apoptosis.