Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 5 1 2013 03 15 76 80 EN Seyed Hamidreza Monavari Antimicrobial Resistance Research Center, Tehran University of Medical Sciences, Tehran, Iran. Hossein Keyvani Department of Virology, Tehran University of Medical Sciences, Tehran, Iran. Hamidreza Mollaie Department of Virology, Tehran University of Medical Sciences, Tehran, Iran. Rouhollah Vahabpour Roudsari Department of Virology, Tehran University of Medical Sciences, Tehran, Iran. 2015 10 16 Background Objectives: The risk of adefovir dipivoxil resistance emergence has increased in lamivudine-resistant hepatitis B infected patients. The mutations known as causing adefovir resistance, rtN236T and rtA181V/T, are detected within the D and B functional domain of the HBV polymerase, respectively. In this study, we intended to determine the pre-existing adefovir-resistance mutations in patients infected with LAM resistant mutants prior to starting adefovir therapy. Material and Methods: The study included 30 patients with chronic hepatitis B with lamivudine resistance mutations in the YMDD motif that experienced viral breakthrough. Results: After alignment of protein coding sequences, the rtN236T mutation was observed in two (6.6 %) patients, while twenty-eight others had neither rtN236T, nor rtA181V/T mutation. All 30 patients were infected with genotype D of hepatitis B virus. Conclusions: The early detection of LAM-resistance mutations may allow a timely chance of therapy to avoid hepatitis flare- up. This data suggests that monitoring of ADV-resistance mutations in ADV naïve patients can be considered in selecting the appropriate anti-viral regimen. https://ijm.tums.ac.ir/index.php/ijm/article/view/645 https://ijm.tums.ac.ir/index.php/ijm/article/download/645/417