Resistance-related mutations in the HIV-1 protease gene of patients treated for 1 year with the protease inhibitor ritonavir (ABT-538)

AIDS. 1996 Aug;10(9):995-9. doi: 10.1097/00002030-199610090-00010.


Objective: To define genotypic and phenotypic resistance patterns following prolonged therapy with the protease inhibitor ritonavir (ABT-538).

Design: Seven HIV-1-infected patients, all but one previously treated with dideoxynucleoside analogues (zidovudine, didanosine, zalcitabine), were treated for 1 year with ritonavir.

Methods: Direct solid-phase sequencing of the protease gene starting from plasma derived viral RNA followed by comparison to phenotypic drug resistance data.

Results: The most frequent amino-acid substitutions occurring upon administration of the protease inhibitor were V82A/F (substrate binding site), I54V (flap region), A71V and L10I. Additional mutations found in more than one patient were I15V, M36I, I84V and I93L. Mutation L63P was found both in pre- and post-ritonavir samples. Phenotypic drug resistance assays confirmed resistance to ritonavir in post-treatment samples (approximately 170-fold) and showed cross-resistance to indinavir (approximately 30-fold) and partially to saquinavir (approximately fivefold). At 1 year of treatment, one patient without known resistance-associated mutations in the protease gene still showed a substantial rise in CD4 cell count accompanied by a more than 2.4 log decrease in RNA viral load. However, at week 78, mutations R8Q, E34K, R57K, L63P and I84V were detected and the treatment benefit was partially lost.

Conclusions: Long-term treatment with ritonavir is associated with the emergence of multiple mutations in the HIV-1 protease gene. The mutations L10I, I54V, L63P, A71V, V82A/F and I84V correspond to known drug-resistance mutations for ritonavir and other protease inhibitors. Phenotypic resistance to ritonavir was detected in a majority of ritonavir-treated patients at 1 year of treatment. In addition, long-term ritonavir treatment selects for cross-resistance to the protease inhibitors indinavir and saquinavir. This argues against sequential therapy with several protease inhibitors. Delayed resistance in one patient was accompanied with a prolonged increase in CD4 cell count and decrease in viral load suggesting a temporary benefit of treatment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Drug Resistance / genetics
  • HIV Infections / drug therapy*
  • HIV Infections / metabolism
  • HIV Protease / genetics*
  • HIV Protease Inhibitors / pharmacology*
  • HIV Protease Inhibitors / therapeutic use
  • HIV-1 / drug effects*
  • HIV-1 / genetics
  • HIV-1 / isolation & purification
  • Humans
  • Molecular Sequence Data
  • Mutation / drug effects
  • Ritonavir / pharmacology*
  • Ritonavir / therapeutic use
  • Sequence Analysis


  • HIV Protease Inhibitors
  • HIV Protease
  • Ritonavir

Associated data

  • GENBANK/AJ002495
  • GENBANK/AJ002496
  • GENBANK/AJ002497
  • GENBANK/AJ002498
  • GENBANK/AJ002499
  • GENBANK/AJ002500
  • GENBANK/AJ002501
  • GENBANK/AJ002502
  • GENBANK/AJ002503
  • GENBANK/AJ002504
  • GENBANK/AJ002505
  • GENBANK/AJ002506
  • GENBANK/AJ002507
  • GENBANK/AJ002508
  • GENBANK/AJ003214