A preliminary study of ritonavir, an inhibitor of HIV-1 protease, to treat HIV-1 infection

N Engl J Med. 1995 Dec 7;333(23):1534-9. doi: 10.1056/NEJM199512073332204.


Background: Ritonavir is a potent inhibitor in vitro of human immunodeficiency virus type 1 (HIV-1) protease, which is needed for virions to mature and become infective. We assessed the safety and efficacy of ritonavir in patients with HIV-1 infection.

Methods: We administered ritonavir orally to 62 patients in one of four dosages during a 12-week trial containing a 4-week randomized, placebo-controlled, double-blinded phase followed by an 8-week dose-blinded phase. We assessed the response with serial measurements of plasma viremia and serial CD4 cell counts.

Results: Fifty-two patients completed the 12-week trial. Diarrhea and nausea were the most common side effects, and reversible elevations in serum triglyceride and gamma-glutamyltransferase levels were the most frequent laboratory abnormalities. Ritonavir had a rapid antiviral effect, with a mean maximal reduction in the number of copies of HIV-1 RNA per milliliter of plasma that ranged from 0.86 to 1.18 log in the four dosage groups. After 12 weeks of treatment, the antiviral effect was partially maintained, with a mean reduction in plasma viremia of 0.5 log. When we used a more sensitive assay for HIV-1 RNA in a subgroup of 20 patients, we found that plasma viremia decreased by a mean of 1.7 log. This antiviral effect was partly sustained at week 12, with a mean reduction of approximately 1.1 log. The patients' CD4 cell counts rose during treatment with ritonavir (median increase, 74 and 83 cells per cubic millimeter at weeks 4 and 12, respectively).

Conclusions: The protease inhibitor ritonavir is well tolerated and has a potent antiviral effect, as shown by substantial decreases in plasma viremia and significant elevations in CD4 cell counts. Expanded clinical trials of ritonavir are warranted.

Publication types

  • Clinical Trial
  • Multicenter Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Antiviral Agents / adverse effects
  • Antiviral Agents / pharmacokinetics
  • Antiviral Agents / therapeutic use*
  • CD4 Lymphocyte Count / drug effects
  • Double-Blind Method
  • Female
  • HIV Infections / drug therapy*
  • HIV Infections / immunology
  • HIV Protease Inhibitors / adverse effects
  • HIV Protease Inhibitors / pharmacokinetics
  • HIV Protease Inhibitors / therapeutic use*
  • HIV-1 / drug effects*
  • Humans
  • Male
  • RNA, Viral / blood
  • Ritonavir
  • Thiazoles / therapeutic use*
  • Treatment Outcome
  • Valine / analogs & derivatives*
  • Valine / therapeutic use


  • Antiviral Agents
  • HIV Protease Inhibitors
  • RNA, Viral
  • Thiazoles
  • Valine
  • Ritonavir