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Sexual health and LGBT population
Living with HIV
Post-exposure prophylaxis (PEP)
You have likely heard of the concept of bacteria resistant to antibiotics (one of the reasons newer and stronger antibiotics are under development). HIV, as a virus, can also develop resistance to the antiretrovirals devised to impede its reproduction.
The ultimate goal of HIV is to replicate itself and thereby ensure its survival. Antiretroviral medications are devised such that they may block the reproduction process at different levels of replication. In the case of HIV, the replication process is so rapid that HIV regularly makes mistakes when copying itself (these errors are called "mutations"). Resistance arises when newly produced copies of HIV virus equipped with mutations are able to reproduce even in the presence of meds!!
Once your virus has developed mutations that instruct it on how to reproduce in the face of medications, your treatment will no longer be able to suppress viral replication. Your viral load is then able to climb and eventually destroy CD4 cells thus weakening your immune system. In an attempt to avoid this decline in your immune system your physician will most likely recommend that you change your treatment regimen.
Another problem with respect to the concept of resistance is that of cross resistance. This is when the virus develops mutation(s) and resistance to one particular medication, yet this/these mutations also confer resistance to other medications (usually in the same class of medications). Cross resistance can render many, if not all, of the medications in the class less effective (some classes of medications are more at risk from cross resistance than others).
It is important to note, that while there are a multitude of medications currently available to combine and treat HIV, your first therapeutic combination prescribed is likely your best bet at controlling HIV infection. Initial or first line therapies are often simpler and better tolerated than medication combinations used once mutations and resistance have developed (second and third line therapies). As resistance develops, there are fewer medications available to combat HIV. As patients progress towards combinations intended to overcome resistant virus, there is often the associated disadvantage of increased number of pills, constraints and side effects, etc.
The bottom line: your first line is your best line of therapy!!