Pharmacokinetics, efficacy, and safety of analgesia with a focus on tramadol HCl

Abstract Chronic pain remains a problem because it is often misdiagnosed and undertreated. Adverse effects and safety concerns associated with many analgesics have limited the use of these agents and contributed to the undertreatment of pain. With regard to the pharmacologic agents most commonly used to manage pain, centrally acting analgesics (e.g., morphine, codeine) are associated with respiratory depression, tolerance, and dependence, and most nonsteroidal anti-inflammatory drugs (NSAIDs) produce adverse gastrointestinal effects. New to the United States, tramadol HCl, which has been prescribed for almost 2 decades in Europe, is a single-entity, centrally acting analgesic that is effective for the management of moderate to moderately severe pain. Although the mechanism of action of this analgesic is not completely understood, animal models suggest that at least two complementary modes of action appear applicable: (1) binding of parent compound and mono- O -desmethyltramadol (M1 metabolite) to the μ-opioid receptor and (2) weak inhibition of norepinephrine and serotonin reuptake. Clinical experience suggests that tramadol appears to have a low potential for abuse or addiction. Results from clinical trials conducted in the United States as well as European postmarketing surveillance studies indicate that tramadol is an effective analgesic that may have a particularly important role in the management of chronic painful conditions.