About irinotecana topoisomerase 1 inhibitor,natural source (plant) derivative ,semisynthetic camptothecin analogue , antineoplastic.mechanism of action of irinotecanbinding of irinotecan and its active metabolite bind to the topoisomerase 1 (which catalyze recombination, repair of dna and also reversible single strand breaks in dna during dna replication) and form a topoisomerase1-dna complex and this prevents relegation of these single strand breaks, finally cell death.interactions for irinotecanother antineoplastic agents: side effects like diarrhoea and myelosuppression may be exacerbated. dexamethasone: lymphocytopenia has been observed when coadministered. diuretics: because of possibility of causing dehydration with diarrhoea, caution should be observed in the use of irinotecan with diuretics.