IT IS AN ANTIVIRAL,SYNTHETIC PURINE NUCLEOSIDE ANALOGUE OF THE NATURALLY OCCURING NUCLEOSIDE DEOXYADENOSINE.INTRACELLULARLY ,DIDANOSINE IS CONVERTED BY CELLULAR ENZYMES TO THE ACTIVE METABOLITE,DIDEOXYADENOSINE 5-TRIPHOSPHATE,WHICH INHIBITS THE ACTIVITY OF HIV-1 REVERSE TRANSCRIPTASE BOTH BY COMPETING WITH THE NATURAL SUBSTRATE AND BY ITS INCORPORATION INTO VIRAL DNA.