Antiretroviral therapy in the treatment-experienced patient.

Despite the growing number of new antiretroviral agents, planning therapy for treatment-experienced patients remains extremely challenging. Cross-resistance within the three currently available classes of drugs limits the number of sequential drug regimens that can be expected to suppress viral replication effectively. An understanding of resistance and cross-resistance, together with judicious use of resistance testing, can help clinicians design better treatment regimens for patients experiencing virologic failure while taking antiretroviral therapy.