 NNRTI-resistant HIV-strains have the occurring mutations mainly in and around the NNIBP affecting the NNRTI binding directly by altering the size, shape and polarity on different areas of the pocket or by affecting, indirectly, the access to the pocket.Those mutations are primarily noted in domains which span amino acids 98-108, 178-190 or 225-238 of the p66 subunit.The most frequent mutations observed in viruses isolated from patients who have been on a failing NNRTI containing chemotherapy are Lys-103N and Tyr-181C.