Drug Resistance Tests to Predict Response to Treatment for HIV Infection

Summaries for Patients are a service provided by Annals to help patients better understand the complicated and often mystifying language of modern medicine.

Summaries for Patients are presented for informational purposes only. These summaries are not a substitute for advice from your own medical provider. If you have questions about this material, or need medical advice about your own health or situation, please contact your physician. The summaries may be reproduced for not-for-profit educational purposes only. Any other uses must be approved by the American College of Physicians-American Society of Internal Medicine.

The summary below is from the full report titled "HIV-1 Genotypic Resistance Patterns Predict Response to saquinavir–ritonavir Therapy in Patients in Whom Previous Protease Inhibitor Therapy Had Failed." It is in the 7 December 1999 issue of Annals of Internal Medicine (volume 131, pages 813-821). The authors are A.R. Zolopa, R.W. Shafer, A. Warford, J.G. Montoya, P. Hsu, D. Katzenstein, T.C. Merigan, and B. Efron.

What is the problem and what is known about it so far?

The human immunodeficiency virus (HIV, the virus that causes AIDS) often becomes resistant to drug treatment. "Resistant" means that the virus's genes have changed so that the available drugs no longer work to destroy it. Special tests for resistance to anti-HIV drugs have recently become available. However, it is not really known whether these tests can help doctors predict which patients will respond to HIV drug treatment.

Why did the researchers do this particular study?

They wanted to find out whether testing for resistance to anti-HIV drugs could help predict which patients would or would not respond to further anti-HIV medicines.

Who was studied?

Fifty-four patients in the HIV clinic of a California teaching hospital were evaluated. Treatment with certain highly active anti-HIV drugs had already stopped working in these patients. The patients were about start receiving a new combination of two drugs, saquinavir and ritonavir, that they had not yet received.

How was the study done?

The researchers did resistance tests on virus obtained from the patients before they started taking the new drugs. They also collected information about the patients that might be helpful in predicting the response to drug therapy: for example, what anti-HIV drugs patients had taken in the past, how often they missed doses of medication, and how advanced the HIV infection was at the time they began the new treatment. They then followed patients to see who responded to the new treatment after 12 and 26 weeks, and who did not.

What did they researchers find?

Only 22 of the 54 patients were responding to the new drugs by week 12, and only 12 were responding by week 26. A previous diagnosis of AIDS, more severe disease at the time the new therapy was started, and the number of different HIV medicines a patient had taken in the past were all helpful in predicting who would respond. Even accounting for these other factors, however, the resistance tests done on the virus itself at the time patients started the new drugs were the best predictors of who would respond to therapy.

What were the limitations of the study?

The number of patients studied was small, and they all came from a single clinic. In addition, only patients receiving one particular anti-HIV medication regimen were studied.

What are the study's implications?

The results of this study support the idea that testing the HIV virus from individual patients for HIV drug resistance might be useful in predicting which patients will and which will not respond to certain types of HIV drug treatment. Many other similar studies will be needed, however, before virus resistance testing can be widely accepted.