Drug levels and HIV

July 2001     View PDF     En español

Recent advances in diagnostic tests, such as viral load and resistance testing, have been extremely useful in advancing the care of people with HIV. Many experts believe the next advance will come from new tests that measure the amount of drug in a person’s blood.

Soon after taking medication, the maximum amount of that drug can be found in your blood. This maximum drug level is called Cmax; and the higher the level, the more likely you’ll experience side effects. Over time, the drug level decreases; and around the time you take your next dose, the lowest level can be found. This level is called Cmin, and the lower the level the more likely drug resistance will develop.

For certain antibiotics, the Cmax is the most important level to consider as it has been shown to correlate with a drug’s effectiveness. However, it has not been established which level shows a relationship with the activity of anti-HIV drugs, although most people believe that the Cmin is likely the most important.

There are many reasons why different aspects of pharmacology can help in managing your anti-HIV therapy. They include measuring drug levels in blood (Therapeutic Drug Monitoring or TDM); measuring drug levels inside cells (intracellular); drug interactions; and protein binding. Read on for more discussion of these areas.