Ritonavir (Norvir)

Published January 25, 2001; Updated October 19, 2011
Susa Coffey, MD
Selected References
8. Tebas  P, Patick  AK, Kane  EM, Klebert  MK, Simpson  JH, Erice  A, Powderly  WG, Henry  K.
Virologic responses to a ritonavir--saquinavir-containing regimen in patients who had previously failed nelfinavir. AIDS. 1999 Feb;13(2):F23-8
[PubMed ID: 10202820]
OBJECTIVES: The effectiveness of a second protease inhibitor in patients who failed an initial protease inhibitor is unclear but believed to be low. It has been postulated, however, that patients who fail nelfinavir may respond differently. We therefore assessed the virologic response to a ritonavir-saquinavir-containing regimen in patients who had previously failed nelfinavir. METHODS: A total of 26 patients enrolled in the nelfinavir clinical trials AG506 and AG511 at our two sites who failed (two consecutive HIV viral loads > 5000 copies/ml; branched DNA assay) were switched to a combination of stavudine 40 mg twice daily, lamivudine 150 mg twice daily, ritonavir 400 mg twice daily and saquinavir 400 mg twice daily. RESULTS: The mean viral load at enrollment in this study was 46 674 copies/ml (range, 1075-146400 copies/ml). The median CD4 cell count was 222 x 10(6)/l (range, 82-448 x 10(6)/l). The median duration of nelfinavir use with a detectable viral load before the switch occurred was 48 weeks. Two patients discontinued the study at 3 weeks. All of the remaining patients (n = 24) reached undetectable viral loads (< 500 copies/ml) that were sustained at week 24 in 17 (71%) out of 24 subjects. The most frequent baseline mutations in the protease gene prior to switching were D30N (13 out of 18), N88D (eight out of 18) and M36I (eight out of 18). The presence or absence of these mutations was not predictive of a short-term virologic response. CONCLUSIONS: Most patients who failed a nelfinavir-containing regimen responded to a switch to a combination regimen with saquinavir-ritonavir.
9. Zolopa  AR, Shafer  RW, Warford  A, Montoya  JG, Hsu  P, Katzenstein  D, Merigan  TC, Efron  B.
HIV-1 genotypic resistance patterns predict response to saquinavir-ritonavir therapy in patients in whom previous protease inhibitor therapy had failed. Ann Intern Med. 1999 Dec;131(11):813-21
[PubMed ID: 10610625]
BACKGROUND: Tests for resistance to HIV drugs are available for clinical use; however, their predictive value has not been fully assessed. OBJECTIVES: To determine HIV-1 genotypic predictors of a virologic response to saquinavir-ritonavir therapy in patients in whom at least one previous protease inhibitor-containing regimen had failed and to compare the predictive value of baseline genotype with that of standard clinical evaluation. DESIGN: Retrospective clinical cohort study. SETTING: University-based HIV clinic. PATIENTS: 54 HIV-1-infected adults treated with saquinavir-ritonavir who had experienced virologic failure while receiving a protease inhibitor-containing regimen for at least 3 months. MEASUREMENTS: HIV-1 reverse transcriptase and protease gene sequences, CD4 cell counts, clinical characteristics, detailed antiretroviral treatment history, and plasma HIV-1 RNA levels at baseline and at three follow-up time points (median, 4, 12, and 26 weeks). Virologic failure was defined as a plasma HIV RNA level greater than 1000 copies/mL. RESULTS: In 22 patients (41%), a plasma HIV-1 RNA level less than 500 copies/mL was achieved by week 12; in 15 patients (28%), this response was maintained through week 26. Clinical characteristics predicting a poorer response included a diagnosis of AIDS, lower CD4 cell count, and higher plasma HIV RNA level (P<0.03). Number of previous nucleoside reverse transcriptase inhibitors, previous protease inhibitor therapy, and duration of previous protease inhibitor therapy were predictors of poorer response (P<0.01). Multivariate regression models revealed that protease mutations present at the initiation of saquinavir-ritonavir therapy were the strongest predictors of virologic response. A model of clinical features explained up to 45% of the variation in virologic outcomes by week 12, whereas the explained variance was 71% when genotypic predictors were included. CONCLUSIONS: In patients in whom protease inhibitor-containing antiretroviral therapy fails, HIV-1 genotype is predictive of virologic response to subsequent therapy. This predictive capacity adds to that of standard clinical evaluation.