Any given immunoassay is prone to c

Any given immunoassay is prone to cross-reactivitywith unrelated compounds. Issues regarding the specificity of PCP immunoassays have been well documented inthe literature. Known potential interferences are tramadol and venlafaxine (1) since both drugs share structuralsimilarities with PCP (Fig. 2).Another potential pitfall in this patient’s presentation involves his use of tramadol. Potential side effects include seizures and serotonin syndrome (2).Both can occur with tramadol monotherapy but aremore likely with concomitant antidepressant usage,particularly of selective serotonin reuptake inhibitors.Reexamination of this patient’s clinical presentationreveals that it is entirely possible that serotonin excesscould have played a role. Although he did not confirm