Effect of cyclobenzaprine on tricyclic antidepressant assays

OBJECTIVE: To evaluate cyclobenzaprine interference on tricyclic antidepressant assays. DATA SOURCES: Literature was identified through a MEDLINE search (1966-August 2004) using the search terms cyclobenzaprine, tricyclic antidepressant, toxicology, and assay. DATA SYNTHESIS: Cyclobenzaprine is structurally similar to tricyclic antidepressants and is often identified as a tricyclic antidepressant on toxicology assays. Older chromatographic assays demonstrate retention time differences of only seconds and nearly identical color stains between cyclobenzaprine and individual tricyclic antidepressants. In comparison, ultraviolet absorption ratios of 4.18 for amitriptyline and 1.85 for cyclobenzaprine are easily distinguished. Spectroscopy also consistently identifies cyclobenzaprine's unique mass-to-charge ratio peaks of 275 and 215 compared with those of amitriptyline, Available bioanalytic techniques are reviewed for their ability to correctly identify cyclobenzaprine and differentiate the drug from tricyclic antidepressants. CONCLUSIONS: When assays are positive for tricyclic antidepressants without a history of their use, an attempt should be made to identify confounders, such as cyclobenzaprine. Newer bioanalytic techniques, such as ultraviolet absorption and mass spectroscopy, accurately identify cyclobenzaprine in such instances.