Phenobarbital
Definition
A long-acting barbiturate (half-life 80-120 h) listed on the WHO Essential Medicines List as a first-line antiepileptic; Schedule IV under the UN Convention 1971 and NDPS Schedule I (psychotropics) in India. Distinguished from secobarbital and amobarbital by GC-MS retention time on DB-5 column.
- Drug class
- Long-acting barbiturate
- Half-life
- 80 to 120 hours
- WHO status
- Essential Medicines List, first-line antiepileptic
- UN control
- Schedule IV, 1971 Convention
- Confirmatory method
- GC-MS retention time on a DB-5 column
Common questions
Why does phenobarbital's long half-life matter in a forensic toxicology case?+
Because it clears slowly, blood levels stay relatively stable over days, which helps interpret a single post-mortem or admission sample without the sharp concentration swings seen with short-acting barbiturates.
How is phenobarbital told apart from other barbiturates in the lab?+
Screening immunoassays cannot reliably distinguish barbiturates from one another, so confirmation relies on GC-MS, where phenobarbital's retention time and mass spectrum on a DB-5 column separate it from secobarbital and amobarbital.
Why is a medicine on the WHO Essential list also a controlled substance?+
Phenobarbital has genuine clinical value for seizure control but also carries dependence and diversion potential, so international drug control treaties schedule it while health authorities keep it on essential-medicine lists for legitimate prescribing.
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