ddC has been shown to have an antiviral effect, and AZT is known to significantly decrease mortality and to reduce the frequency of opportunistic infections in patients with AIDS or advanced ARC. After 1 year of AZT therapy, the effectiveness tends to diminish and patients progress with more opportunistic infections and higher mortality rates. This may be due to the emergence of AZT resistant virus isolated from some patients who have been on long-term AZT therapy. These isolates were still sensitive to ddC. A study of long-term effectiveness of ddC in patients with AIDS or advanced ARC who have been on long-term AZT therapy is warranted because (1) ddC has antiviral activity, (2) there is no blood toxicity associated with taking ddC, and (3) the effectiveness of ddC in test tube studies does not seem to be diminished by decreased effectiveness of AZT.~AMENDED: AZT will be administered orally every 4 or 5 hours. Patients in the second arm discontinue AZT and take ddC as two tablets every 8 hours. Duration of the study is 1 year with interim analysis done at 6 months after 75 percent enrollment and at end of the study. Original design: Patients with AIDS or advanced ARC who have been receiving at least 500 mg/day of AZT for at least 48 weeks are randomized to 1 of 2 treatment arms. Patients in the first treatment arm continue their current dose of AZT.
To compare the effectiveness of zalcitabine ( dideoxycytidine; ddC ) therapy to zidovudine ( AZT ) in the treatment of AIDS or advanced AIDS related complex ( ARC ) in patients who have already received at least 1 year of AZT therapy and to define the safety profile.~ddC has been shown to have an antiviral effect, and AZT is known to significantly decrease mortality and to reduce the frequency of opportunistic infections in patients with AIDS or advanced ARC. After 1 year of AZT therapy, the effectiveness tends to diminish and patients progress with more opportunistic infections and higher mortality rates. This may be due to the emergence of AZT resistant virus isolated from some patients who have been on long-term AZT therapy. These isolates were still sensitive to ddC. A study of long-term effectiveness of ddC in patients with AIDS or advanced ARC who have been on long-term AZT therapy is warranted because (1) ddC has antiviral activity, (2) there is no blood toxicity associated with taking ddC, and (3) the effectiveness of ddC in test tube studies does not seem to be diminished by decreased effectiveness of AZT.