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Monitoring antiviral therapy
Stated briefly, the goals of antiviral therapy are to enhance immunity and delay or prevent clinical advancement to symptomatic disease without inducing important side effects. Currently, the best marker of a drug's activity is a decrease in the viral load. Sometimes, however, the amount of virus will fluctuate spontaneously. Changes of less than 3-fold, such as from 30,000 to 10,000 copies per mL, may not be clinically meaningful. No treatment decisions should be made, therefore, based on a single measurement of the viral load. Although the CD4 cell count is expected to stabilize or increase as a result of effective therapy, CD4 measurements also can fluctuate spontaneously and changes should be interpreted cautiously.
Ideally, prior to initiating treatment, the viral load and the CD4 cell count should be checked twice over a 1 to 4 week period. The viral load test should then be repeated after 2 to 4 weeks of treatment to assure that the therapy is working. If the patient has never been treated before, and is beginning a regimen thought to be highly active, the amount of virus should decrease by 10 to 100-fold during this interval. The best response to treatment would be for the viral load to decrease to undetectable levels. Assuming an optimal response to a new regimen, the viral load should decrease gradually to fewer than 500 copies by 8 to 12 weeks and fewer than 50 copies by 16 to 24 weeks. The appropriate strategy for managing patients who are taking the medication as prescribed but who do not achieve these viral milestones, has not been defined. The options in this situation include adding one or two additional drugs, changing all of the medications, or continuing treatment with careful observation. Patients who have taken numerous antiviral drugs previously would be expected to have a less than complete response to treatment. The reduction of their viral load, therefore, will likely be more modest. Regardless, a change of less than 3-fold suggests that the medications are not effective or the person is not taking his or her medications.