Butalbital
Butalbital. Short-acting barbiturate — GABA-A receptor positive allosteric modulator. Combined with acetaminophen + caffeine (Fioricet) for… Oral half-life 35 h.
Short-acting barbiturate — GABA-A receptor positive allosteric modulator. Combined with acetaminophen + caffeine (Fioricet) for tension-type headache + migraine in legacy use. Schedule III; medication-overuse headache + dependence concerns limit current guidelines' enthusiasm. PK (Fioricet label, butalbital component): Well-absorbed from GI tract (F ~0.95 — textbook for short/intermediate-acting barbiturates), t½ 35 h (intermediate-acting), elimination 59–88% renal as parent or metabolites. Vd ~0.8 L/kg (~56 L, textbook barbiturate). The 35-h t½ underlies the rebound-headache risk on chronic Fioricet use — multi-day accumulation at qid dosing. Tmax not in the label; co-formulated APAP (t½ 1–3 h) + caffeine (t½ 3 h) clear long before butalbital.
PK: no PubMed primary exists for butalbital, so this record stays label-cited by necessity and now says so. The volume of 0.8 L/kg does appear verbatim in a human case report (PMID:29124988), but as a BACKGROUND STATEMENT rather than a measurement, and the half-life of 35 h remains unverifiable against any abstract. F 0.95 and ka 1 /h are dropped: both were invented beyond what the quoted label states, which says nothing about either.
Pharmacokinetics
- Oral — t½ 35 h · Vd 56 L
Sources: PMID:29124988