Frequency and Mutation Patterns of Resistance in Patients with Chron- ic Hepatitis B Infection Treated with Nucleos(t)ide Analogs in Add-On and Switch Strategies

Background: treatment for chronic hepatitis b (chb) has improved over the last 10 years mainly due to the development of effective oral antiviral agents [nucleoside/nucleotide analogs (nucs)]. objectives: the aim of the present study is to identify the frequency and major patterns of resistance to the hepatitis b virus (hbv) in a turkish population of chb patients treated with nucs using add-on and switch therapy strategies.patients and methods: the investigation involved a total of 194 patients (88 were treated using add-on therapy, and 106 were treated using switch therapy). we analyzed the hbv polymerase gene by amplification and direct sequencing procedures.results: primary drug-resistance mutations were detected in 84 patients (43%; 42 in add-on therapy, and 42 in switch therapy) taking lamivudine (lam), 10 patients (5%; 6 in add-on therapy, and 4 in switch therapy) taking entecavir (etv), and 16 patients (8%; 8 in add-on therapy, and 8 in switch therapy) taking adefovir (adv). the most common lam and etv resistance mutations were rtm204i/v, rtl180m and rtt184a/i/s, respectively, while rta181t/v and rtn236t substitutions were the most frequently observed adv resistance mutations. conclusions: patients with chb who developed nuc resistance were managed using 2 different rescue strategies. the frequency and mutation pattern of resistance were similar in patients treated with add-on and switch strategies. these findings may be helpful in the management of rescue strategies in lam-resistant patients.