What is the definition of half-life (t 1/2) in the context of status epilepticus treatment, particularly for patients with a history of seizures or epilepsy?

Status Epilepticus t1/2 Definition

The term "t1/2" in status epilepticus does not refer to a half-life definition but rather represents a temporal threshold: the operational treatment timepoint has been reduced from the traditional 30-minute definition to 5 minutes, meaning any seizure lasting 5 minutes or longer should be treated as status epilepticus. 1, 2

Evolution of the Temporal Definition

• Status epilepticus was traditionally defined as 30 minutes of continuous seizure activity or recurrent seizures without return to full consciousness between episodes 3
• The operational definition has been updated to 5 minutes for treatment purposes, reflecting the understanding that seizures lasting beyond 5-10 minutes are unlikely to cease spontaneously and become progressively more difficult to control 1, 4
• The 2015 ILAE definition introduced different time points for various SE subtypes (convulsive, focal, and absence SE), emphasizing that "time is brain" due to progressive synaptic receptor changes that create a more proconvulsant state 4

Clinical Rationale for the 5-Minute Threshold

• Once a seizure has lasted 5-10 minutes, it is unlikely to stop spontaneously, and the longer it continues, the more difficult it becomes to control pharmacologically 3
• This "therapeutic interval" represents the critical window for intervention with first-line benzodiazepines 3
• Progressive changes in GABA and NMDA receptors occur with prolonged seizure activity, increasing both treatment resistance and risk of permanent brain injury 4

Practical Application

• Any patient arriving at the emergency department with ongoing seizure activity should be presumed to have status epilepticus and treated immediately with benzodiazepines 1, 3
• The 5-minute operational definition applies specifically to convulsive status epilepticus, while focal and absence SE may have different temporal thresholds 4
• Prehospital and ambulatory interventions should focus on this early therapeutic window using intramuscular, rectal, oral, or intranasal benzodiazepines 3

Common Pitfall to Avoid

• Do not wait for the traditional 30-minute mark to initiate treatment—this outdated definition is associated with significantly worse outcomes, higher treatment resistance, and increased mortality 1, 3, 4
• The delay in treatment beyond 5 minutes allows progression from easily reversible seizure activity to refractory status epilepticus with mortality rates escalating from 5-22% to 65% in refractory cases 2