What do the suffixes--XR, ER, Chrono, Chronosphere--really mean as it pertains to modified-release antiepileptic drugs?

Epilepsy is a disease requiring chronic therapy with antiepileptic drugs (AEDs). Many conventional AEDs currently available have either too rapid an absorption or elimination, requiring the patient to take multiple doses per day, which may adversely impact adherence or cause peak-related side-effects. Consequently, some AEDs with immediate-release characteristics have been modified to prolong absorption and/or reduce peak serum concentration, enabling dosage regimen simplification. Modified-release (MR) AED formulations have been labelled with various suffixes or names ('XR, ER, -Chrono, -Chronosphere'), but such labelling may not adequately distinguish those MR AEDs with the most prolonged absorption or unique formulation characteristics. Such suffixes lack precise definition.

We identified the formulation characteristics of currently available MR AEDs, attempting to distinguish them by suffix designation.

Nine MR AED formulations, representing six different AEDs, were characterized, utilizing information from FDA-approved inserts (2001 +) and published literature.

The formulation characteristics of commercially available MR AEDs are quite variable and do not appear to correlate with their brand name suffix.

When all MR AEDs are compared, suffix designations do not provide distinguishable information about formulation characteristics. Clarification of MR AED suffix terminology may be warranted.