Treatments using AZT alternating with ddC are being evaluated in ongoing trials with a goal of reducing the toxicity of each while maintaining antiviral effects. In addition, AZT and ddC may work together in a way that both drugs can be taken at lower doses or less frequent intervals when given together. If the doses can be reduced, then toxicity associated with long-term use of one drug may be reduced. Combination of AZT and ddC might reduce the likelihood of the emergence of resistant mutants. Recent studies indicate a reduced sensitivity of HIV isolated from patients after prolonged AZT therapy. Although the clinical significance of this finding is not clear, it would indicate that these combination studies are all the more important. HIV strains with decreased sensitivity to AZT are still sensitive to ddC.