Nucleoside (acid) analogues is currently Clinical important in the treatment of hepatitis B antiviral drugs, such drugs through direct inhibition of HBV DNA replication, thereby improving the liver histological lesions, retard the progress of hepatitis B disease, reduce complications from occurring. But long-term treatment in HIV drug resistance is such a common issue facing. The anti-viral drug resistance can lead to virologic rebound and worsening of the illness. The United States NIH in 2006 hepatitis B treatment session (Lok A, et al. Program of the 2006 management of Hepatitis B virus meeting, 2006), and in 2006 the United States Institute of digestion by some experts of the “diagnosis and treatment of hepatitis B norms” (Keeffe E, et al. Clin Gastroenterol Hepatol, 2006), the virus was agreed that the definition of resistance (Figure 1): genotype resistance is direct sequencing of PCR products used Determination HBV polymerase mutation is resistant phenotype in vitro cell culture or activity proved resistant variation; virology rebound treatment refers to treatment of HBV DNA than the minimum value increased ≥ 1 log; Health rebound it refers to the chemical reached after initial response to treatment ALT increased, which gene usually first-resistant rebound in virology, and virology rebound and rebound ahead of the chemical hygiene.
HBV clinical implications of drug resistance
Drug resistance is the long-term anti - hepatitis B virus treatment of serious clinical problem. The HBV nucleoside (acid) analogues resistance after clinical consequences of the following: can lead to virologic rebound, the Health and chemical backlash occurred serology recurrence; liver disease progress, such as possible liver disease and acute exacerbation of liver failure, liver transplantation needs or died of liver transplantation due to hepatitis B antiviral drug resistance and failure. Follow-resistant virus can also affect the anti-virus treatment efficacy so that the effect of poor follow-up or treatment resistant rate increased resistance also may lead to the spread of the virus.
Liaw, and so the studies show that lamivudine - resistant mutations can lead to long-term treatment of patients with cirrhosis and decreased disease progress. Another lamivudine (Liaw et al. N Eng J Med, 2004) long-term treatment of patients with liver cirrhosis, according to obtain sustained virologic response was significantly higher than that the survival rate of patients with drug resistance YMDD mutation and no response was virology the patients (P = 0.001), thereby reducing the occurrence of resistance suggested that the effect of a decrease of survival time in patients with liver cirrhosis. Hepatitis B treatment methods>>>
Potent inhibition of virus barrier and the impact on resistance
Colonno annual meeting in 2006 AASLD mentioned in the report, when the virus completely inhibited when, on the one hand drug-sensitive strains were the maximum inhibition, on the other hand resistant mutant viruses have also decreased significantly when the virus is not completely inhibited, the virus also in reproduction, to increase the likelihood of drug resistance mutations. Potent anti-viral drug resistant virus with the “high-barrier,” the first is that the pharmacokinetics barriers that drugs reach the target organ with the concentration required for the concentration of virus inhibition ratio, drugs reach the target organ concentrations higher inhibit virus the lower the concentration required, the greater the ratio, in a “high pharmacokinetics barriers”; Second, the high number of barriers need mutant gene loci simultaneously can produce resistance; 3 refers to the viability of mutant strain of the virus.
The diagnosis and monitoring of drug resistance
American Institute in 2006 released to digest the diagnosis and treatment of hepatitis B virus resistance to the standardized diagnostic criteria: PCR determination that the level of serum HBV DNA at the lowest level in more treatment increased ≥ 1 log, can be identified as virology rebound. The proposed treatment standards for acceptance should lamivudine - treated patients every 3 to 6 months to monitor 1st; adefovir dipivoxil or entecavir for treatment after one year, every six months should be monitoring 1st; on the progress of the liver patients should be monitored on a regular basis, that is, every three months to monitor the 1st. Currently in clinical and laboratory monitoring widely used by the virus resistant HBV DNA methods have rebounded nucleic acid hybridization and PCR method, the higher the sensitivity of the method can be more resistant to earlier monitoring. Foreign resistant genotype detection method for INNO - LiPA HBV DR2 and PCR direct sequencing, the former high sensitivity, but can only detect the known resistance gene loci, the kit has been used in clinical latter sensitivity lower, but can detect known and emerging resistance gene loci, mainly used for laboratory research.
The current HBV nucleoside (acid) analogues resistance characteristics
At present both in vitro and in vivo experiments have proved that with the resistance of the P gene variation, different nucleoside (acid) analogues resistant strains of variation is not consistent sites (Figure 2), such as lamivudine resistance-associated point mutations M204V / I, L180M, and other adefovir related mutation point for N236T, for the Beef as M204I, that is to say, the virus only need a bit mutation can occur resistance to these drugs, and a TU entecavir virus rebound need L180M and M204I / V + T184 or S202 or M250’s three-point mutation, said Mingen entecavir resistance genes with high barriers; another lead TU entecavir resistance in three sites mutation, including two lamivudine resistance mutations, that is to say the TU entecavir resistance must be built on the basis of lamivudine resistance, lamivudine therapy can elect lamivudine - resistant point mutations can also elect of entecavir for resistance mutations.
Lamivudine treatment five years resistance rates close to 70 percent adefovir treatment appeared resistant to lamivudine time later, but for five years, HBeAg-negative patients with primary drug resistance genotype rate was 29 percent, , HBeAg positive patients resistant virus led to the rebound rate was 20%; than stavudine for the treatment for one year, the initial treatment of patients with resistance rebound rate of 4.4% (HBeAg positive), 2.7% (HBeAg negative), 2, when it rose to 21.6 percent, 8.6 percent.
TU entecavir resistance data for three years, three years for a total of three cases of newly diagnosed patients in TU entecavir resistance mutations, these three patients in the baseline at the existence of lamivudine - resistant mutations or TU for the Kahuijia lamivudine - resistant mutations, three years because of resistance led to the virology rebound <1% (Table 1). The reasons for the low rate of drug resistance attributed to TU first entecavir have potent antiviral activity, followed by the resistance gene with high barriers need three sites at the same time can produce drug resistance mutations.
Resistance prevention
Based on the occurrence of HIV drug resistance and the degree of inhibition virus closely related to viral load can be reduced to the level of uncertainty in the resistance may be, it should use potent antiviral drugs, rapid and sustained inhibit viral load to the level of unpredictability At the same time we should select high-resistance gene barriers antiviral drugs; In addition, the increase in compliance, early response is not satisfactory and timely manner to avoid dressing change sequential single-drug treatment, but also help to prevent the occurrence of resistance.
The handling of drug resistance
After emerging resistant virus usually has the following approach: stop current therapy; continue the current treatment; plus another antiviral drugs; to switch to another anti-viral drug. Now that the current treatment and to stop the current treatment, have been reported in the literature can cause acute exacerbation of hepatitis and even liver compensated and should not be used. The current recommended after two methods, the specific approach: ① in lamivudine - resistant, it can increase or switch to adefovir dipivoxil, or switch to TU entecavir; ② adefovir dipivoxil resistance , plus lamivudine or can switch to TU entecavir; ③ TU entecavir resistance, it can increase or alone adefovir dipivoxil. How drug hepatitis patients>>
Summary
Antiviral drug resistance in the long-term treatment of Hepatitis B is a major clinical problem, virus resistance will lead to serious clinical outcomes, and the need for close monitoring. TU entecavir (Bo Road), is the lowest incidence of drug resistance nucleoside analogues. Nucleoside analogues in the initial treatment of patients through the use of potent antiviral drugs, the use of high-resistance gene barriers antiviral drugs, and enhance the patient’s compliance, HBV resistance can be reduced time delay and resistance rates. When the resistance occurred, it should consider the use of potent antiretroviral therapy or in combination.