Drug infusions for the diagnosis and treatment of chronic pain.

Diagnostic infusion therapy has several advantages over other routes of drug administration in the management of chronic pain. Although systemic side effects may occur, the procedure is relatively noninvasive and is generally well tolerated by patients. Infusion techniques have a potential use in the blinded evaluation of a patient's response to a specific therapy, and thus may minimize placebo responses associated with the more invasive diagnostic nerve blocks. Infusion tests may be useful prognostic indicators of the potential efficacy of a class of oral drugs in a patient. This article reviews the scientific and clinical background behind the major classes of drugs used in diagnostic infusion testing, namely local anesthetics, opioids, and a-adrenergic blockers. Clinical application of these agents in the management of chronic pain also is outlined.