The goal of combination therapy, to improve the length and quality of your life, is best achieved by suppressing viral replication to below detectable levels as measured on an ultrasensitive viral load assay, and keeping it there.
However, this is not always achievable with a given combination and it sometimes needs to be changed.
There are a number of reasons why a particular combination of anti-HIV drugs fails. These include poor adherence to the drugs and sub-optimal blood levels of anti-HIV drugs. In the latter case, drug levels may be low in some patients because of an individual’s physiology and not their adherence to the regimen. The therapy is not failing because of the development of drug-resistant HIV, but because the drugs are being absorbed at a rate different from that in other people. This can be straightforwardly investigated by drug level monitoring and may avoid the necessity of changing the drug combination. Dose adjustment may be all that is necessary.