Symptom relapse following switch from Celexa to generic citalopram: an anxiety disorders case series

Generic agents do not require large clinical trials of safety and efficacy to enter the market, although they must demonstrate both pharmacological and bioequivalence to the brand name drug. Bioequivalence is attained when the extent of absorption of the generic falls within an FDA predefined range relative to the brand name drug. This potential variation in bioequivalence is not thought to be clinically meaningful, however, there are reports of a lack of therapeutic equivalence between some generic medications and the brand name. This study examines the potential risks posed by a switch from Celexa to generic citalopram. Twenty patients at an Anxiety Disorders Clinic who were unknowingly switched to generic citalopram, from Celexa (Lundbeck, Montreal, Quebec, Canada) and experienced a re-emergence of their anxiety symptoms or development of new adverse events are described in this case series report. The mean time for re-emergence of symptoms or development of adverse events was 3.4 +/- 1.6 weeks (range 0.5-8 weeks). All patients reestablished previous treatment response with a change back to Celexa in a mean time of 3.8 +/- 2.6 weeks (range 0.7-12 weeks). Given these results, it is important for clinicians to be aware of the potential for loss of treatment effect or symptom re-emergence posed by a switch to a generic agent. Randomized, double blind, controlled investigations would likely provide useful information as current bioequivalence and pharmacological equivalence do not necessarily translate into clinical equivalence.