HIV may develop persistence to a particular medication if it is taken intermittently or in insufficient doses. Such persistence is called resistance.
Development of virus resistance to medications means that the efficiency of these medications reduces, and they would not have the same efficiency as before, or will not have an effect at all.
HIV is constantly mutating. Adherence to dosing and regimen of antiretrovirals makes it possible to maintain the HIV load at low level and does not lead to the development of mutations. Missing a regular dose of medication is possible without serious impact on efficacy. However, it is very important that the noncompliance with therapy regimes does not become regular. Risks arise only when deviating from the dosage regimen is repeated or systematic.
Mutations causing resistance usually occur with a detectable viral load. If the viral load does not decrease for several months, an analysis for resistance should be conducted and if necessary, a possible change in therapy.
After prolonged use of the same therapy regimen, the virus can also mutate and develop resistance to the drugs used. In this case, one must also change the antiretroviral therapy for a more effective one.