Understanding HIV Drug Interactions
Drug interactions occur when one medicine changes the effects or concentration of another medicine. Antiretroviral drugs can interact through several mechanisms, including changes in absorption, metabolism, and elimination. The significance of an interaction depends on the particular HIV regimen and the other medication being used.
Common factors involved in HIV drug interactions include:
- Changes in absorption: Antacids and products containing calcium, magnesium, aluminum, iron, or other minerals can interfere with the absorption of some antiretroviral medicines.
- Changes in metabolism: Some HIV medicines affect enzymes such as CYP3A4, which are involved in processing many other medicines.
- Changes in drug transport: Certain antiretroviral medicines can affect transport proteins involved in moving medicines through the body.
- Food and stomach acidity: Some HIV medicines have specific food or acidity considerations that can affect their absorption.
Because different antiretroviral medicines have different interaction profiles, an interaction involving one HIV medicine does not necessarily apply to another medicine in the same broad treatment category.
Possible Health Effects of Drug Interactions
The effects of an interaction depend on whether the interacting medicine causes drug levels to rise or fall. Increased exposure can sometimes increase the likelihood or severity of medication-related toxicity, while decreased exposure can potentially reduce therapeutic effectiveness.
Possible consequences include:
- Increased side effects: Higher concentrations of a medicine may increase the risk of adverse effects.
- Reduced treatment effectiveness: Lower concentrations of an antiretroviral medicine may affect its ability to control HIV.
- Changes in the effects of other medicines: Some HIV medicines can increase or decrease concentrations of medicines taken for other conditions.
- Treatment complications: Significant interactions may require changes in dosing, timing, monitoring, or the medicines being used.
- Risk of resistance when HIV treatment is not adequately effective: Maintaining effective antiretroviral therapy and taking medicines as prescribed are important for reducing the risk of drug resistance.
Some interactions are particularly important because they involve medicines used for infections or other conditions that may occur alongside HIV. NIH guidance includes specific interaction tables for medicines used to prevent or treat opportunistic infections.
Healthcare professionals may review the complete medication list before adding or changing treatment. This review should include prescription medicines, nonprescription products, vitamins, minerals, and herbal or dietary supplements. Depending on the interaction, clinicians may recommend separating doses, adjusting a dose, choosing another medicine, or monitoring for changes in treatment response or toxicity.
People taking HIV treatment should therefore avoid starting or stopping another medicine or supplement without discussing it with their healthcare professional. Keeping an updated list of all medicines can make interaction checks more accurate and help healthcare providers identify potential problems before they occur.