text: Hi. I'm going to try to answer this the best I can.  I've never heard of nigrogen base analogs: maybe you meant nucleotide base analogs? Typically (especially in HIV) the nucleotide base analogs take the place of a normal base, making the transcription of the virus 'inaccurate' with the mistake in it.  This slows down viral replication, and helps inhibit the spread of the virus.