New Developments in HIV Drug Resistance and Options for Treatment-Experienced Patients

• Introduction
• Epidemiology of HIV Resistance
• Predicting Treatment Response Based on Resistance Scores
  • Refinement of the Genotypic Resistance Score for Tipranavir
  • The Value of Discussing Resistance Test Results With HIV Resistance Experts
  • Interpreting Genotype Results for Patients With Low Viral Load
• Clinical Implications of HIV Drug Resistance to Therapy With Approved Antiretrovirals
  • Atazanavir
  • Tenofovir
  • The Impact of Emerging Resistance Mutations on Treatment Response
• The Impact of New Antiretrovirals on Treatment Options for Multidrug-Resistant Patients
  • TMC114
  • TMC125
• Conclusion/Closing Comments
• References

Introduction

The emergence of drug resistant HIV in patients failing therapy is a result of two processes: the emergence of pre-existing genetic variants and the selection of drug-resistant virus as a result of selective pressure. There are a multitude of reasons for HIV's enormous genetic variability -- not only is the HIV reverse transcriptase (RT) error-prone, but there is also an absence of any enzymatic proofreading activity and a high rate of HIV replication in vivo. In patients who are maintained on a failing regimen, the insufficient potency of the treatment means viral replication is ongoing. This risks the accumulation of additional mutations as well as increasing cross-resistance.

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