Side effects, drug levels and genetics

Most drugs are approved at one standard dose even though different people absorb drugs differently. This can be related to differences in our genes and is a new area of research called pharmacogenetics.

For example, tiny differences in your DNA can explain the differences in levels of drugs including efavirenz, nevirapine and atazanavir.

Just as the blood levels of a drug affect how effective it is, they also affect the chance of side effects.

Drug levels for some HIV drugs can be checked using a test called therapeutic drug monitoring (TDM). The dose can then be changed if they are too high or too low.

  • Protease inhibitors, NNRTIs and integrase inhibitors can be measured.
  • Nukes (3TC, FTC, abacavir, tenofovir DF and TAF) can not be measured. This is because the important levels of these drugs are inside cells and the tests measure drug levels in blood.

TDM is not routinely used but it is important in some situations.

Information on TDM

Drug interaction websites

Last updated: 1 August 2016.