| Lamivudine, a kind of nucleoside analogues, as an antiviral drug, has been worldwidely used for the treatment of chronic hepatits B. The advantage of this drug that it can make rapid decrease in HB V DNA level and improve the liver function and liver histology has been proven by many clinical trials. However, drug-resistance will emerge during long-time lamivudine therapy mainly due to YMDD motif mutant occurred in HBV polymerase gene region. The clinical characteristics of the mutant is: rebound of viral DNA, ALT flare, even acute exacerbation. Our work is to evaluate mis-matched PCR- RFLP, direct sequencing, clone sequencing, these three methods' effect in detecting YMDD mutant, to find some predictive factors about emergence of lamivudine resistance and observe the relationship between combination therapy including thymosin-al. and lamivudine and emergence of YMDD motif mutant We hope our study can offer some advice to clinical doctor for using antiviral drugs reasonably.A method on the basis of mis-matched PCR-RFLP was designed to analyze the mutation. Eighty patients belong to a cohort of patients who have used lamivudine for antiviral therapy followed-up in our department for long time were studied. All these patients' serums were collected and YMDD mutant was tested by mis-matched PCR-RFLP and sequence analysis, then the relationship between YMDD mutant and all these samples' clinical data were analyzed Result: The total drug-resistant rate of the first year, the second year and the third year during the therapy is 12.5% (10/80),37.3% (19/51), 83.9% (26/31), respectively (P<0.05) ; The total drug-resistant rate per year during the therapy didn't show any significant difference between male patients and female patients (the first year: 9.68% vs 22.2%; the second year: 32.5% vs 54.55%), the patients at baseline with high ALT level and low ALT level (the first year:12.5%vsl0.9%; the second year:33.3% vs 34.3%), pre-therapy HBeAg-negative patients and HBeAg-positive patients (the first year: 13.5% vs 10.7%; the second year: 40.5% vs 28.6%). The post-therapy ALT level is higher in mutant group than non-mutant group (52.2% vs 5.77%, P<0.05).Forty-four patients belong to a cohort of patients who were included in a clinical trial were also studied Some other parameters' relationship with YMDD mutant were observed. The result: the drug-resistant rate in group G2S2 (liver biopsy) is higher than group G1S1 (24.0% vs 0, P<0.05); The drug-resistant rate in Patients with high HBV-DNA baseline level and low HBV-DNA baseline level is of no statistical difference (15.4% vs 16.1%, P>0.05). There is no significant difference of the YMDD-mutant incidence between the combination- therapy group and monotherapy group(25% vs 8.33%, P>0.05).From above-mentioned results, we can draw four conclusions: Firstly, The simple method to detect YMDD mutant was rapid and efficient; Secondly, The increased risk of lamivudine resistance is associated with the therapy lasting-time, liver biopsy, but not with gender, pretherapy HBeAg, HBV-DNA level at baseline and ALT level at baseline; Thirdly, The prilimiriary result show that: combination-therapy of thymosin-a i plus lamivudine can't reduce the risk of lamivudine resistance; Fouthly, Serum ALT level will elevate after the emergence of drug-resistence.
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