Drug resistance
Drug resistance describes the ability of HIV to replicate in the body despite the presence of an antiviral drug. Mutations in the viral genome are the cause of resistance. The emerged mutations form the basis of the new virus population, whose replication the antiviral drug cannot suppress.
Reasons for drug resistance
Emerging mutations: The replication process of HIV is highly error-prone. Due to this, the virus mutates almost every time a new copy is made. A higher replication rate of the virus causes more mutations to emerge, and so the chance of developing a resistance mutation rises. The more resistance mutations emerge, the more drug classes fail to suppress the virus. Although the number of treatment choices become more restricted with drug resistance, it is important to know that there are usually more available options and that treatment regimens can be tailored to meet individual medical and life style needs.
Changing treatment: When a drug resistant mutation emerges, current treatment needs to be changed because otherwise the resistant virus is able to multiply, gaining more resistance mutations.
Reducing the risk of resistance: Research has shown that the most effective suppression of HIV occurs when all medication is taken at the right time, in the right dose every day. Missing a dose means that the virus is not being suppressed as much as it should be and so has the opportunity to replicate. More HIV replication provides more chances for the virus to mutate and therefore become resistant to therapy.
Types of resistance
Drug resistance can be described in three forms: clinical, genotypic and phenotypic resistance.
Clinical resistance is displayed by rapid replication of HIV despite the presence of antiretroviral drugs in the body.
Genotypic resistance presents itself in mutations of the virus' genetic code. The mutations that have been associated with resistance against antiretroviral medications can be determined by genotypic resistance tests.
Phenotypic resistance refers to the replication capacity oft he virus in the presence of one drug. Phenotypic resistance tests determine the responsiveness to one antiretroviral drug, by measuring what concentration is required in order to reduce HIV replication.
Genotypic and phenotypic resistance can be measured by laboratory tests. With algorithms it can be ealenlated how mutations (genotypic changes) affect the phenotype (genotype to phenotype-algorithms).
Multiple resistance
Cross-resistance can occur within medications of one drug class. In case of cross-resistance, the virus, resistant to one drug, also shows resistance to other drugs of the same class. Knowledge of cross-resistance is important if a change in treatment is required due to resistance.
Multi-drug resistance: Resistance to more than one drug.
