Rifampin
Rifampin. Bactericidal — binds bacterial RNA polymerase β-subunit. Most potent CYP3A4 inducer in clinical use (also CYP2C9, CYP2C19, CYP2B6… Oral half-life 1.9 h.
Bactericidal — binds bacterial RNA polymerase β-subunit. Most potent CYP3A4 inducer in clinical use (also CYP2C9, CYP2C19, CYP2B6, UGT, P-gp via PXR activation). Dramatically lowers warfarin, OCs, methadone, statins, transplant immunosuppressants, anti-HIV agents.
PK: Pargal 2001 (PMID:11263520), 12 healthy volunteers, verbatim "3.57 (34.85) h, at the 450 mg dose (tablet)" — scoped to a single 450 mg oral tablet in treatment-naive subjects, since the same paper reports 5.44 h at 600 mg and calls the difference significant. ka, V and F dropped 2026-09-06: that abstract states none of them, and ka is contradicted in kind because the paper concludes rifampicin shows "zero order absorption". Not adopted, to avoid mixing populations: V 53.2 L and CL/F 19.2 L/h in 261 TB patients at induced steady state (PMID:18391026), and absolute bioavailability "87% and 71% for rifampicin" fasted and fed (PMID:26661397). The IV route was REMOVED — its whole block cited this oral-only study. CAVEATS: rifampicin autoinduces its own metabolism, clearance rising from 7.76 L/h at first dose by 1.82-1.85x at steady state with AUC falling 41-42% over ~40 days (PMID:22252827), so this single-dose half-life understates chronic clearance; and at high doses bioavailability falls while clearance saturates (PMID:28653479). PK: THE RECORD WAS RENDERING ENTIRELY AGAINST SILENT DEFAULTS, AND ITS OWN NOTE NAMED THE VALUES THAT FIX IT. A 2026-09-06 pass dropped the absorption rate, the volume and the bioavailability because the cited abstract states none of them — a correct diagnosis — and recorded the verbatim alternatives it declined to adopt "to avoid mixing populations". BUT THE DEFAULTS IT FELL BACK ON ARE NOT A POPULATION AT ALL: half a litre per kilogram and a bioavailability of 0.9 are unsourced constants, invisible on every surface, and they asserted a volume a third below the published one. The two declined numbers turn out to come from ONE population fit of ONE cohort of two hundred and sixty-one patients — "The typical population estimate of oral clearance was 19.2 liters x h(-1), while the volume of distribution was estimated to be 53.2 liters" — so adopting them mixes nothing. Both are APPARENT, which that abstract confirms in the same breath ("A strong correlation between clearance and volume of distribution suggested substantial variability in bioavailability"), so bioavailability is pinned at unity rather than stored, and the verbatim absolute figure from a different study — "87% and 71% for rifampicin" fasted and fed — is deliberately NOT stored beside an apparent volume. THE HALF-LIFE MOVES WITH THEM, to the one that pair implies. THAT IS A DELIBERATE CHANGE OF STATE: the abandoned 3.57 h is a single-dose figure in treatment-naive subjects, while this drug INDUCES ITS OWN METABOLISM and is taken daily for months, so the induced steady state is the one users occupy — the moclobemide reasoning, and the two states differ 1.86-fold, inside the band that kept efavirenz and rifabutin rather than the one that stripped carbamazepine. ONE ITEM IS LOGGED: that paper models absorption through a transit chain and this record has no absorption rate at all, so it renders at the default; a zero-order duration would carry it better.
Pharmacokinetics
- Oral — t½ 1.9 h · F 100% · Vd 53.2 L
Related compounds
- Warfarin — major
- Ethinyl Estradiol — contraindicated
- Midazolam — contraindicated
- Atorvastatin — major
- Simvastatin — major
- Cyclosporine — major
- Tacrolimus — major
- Losartan — warn
Sources: PMID:8549036, PMID:16084850, PMID:11180018, PMID:1424418, PMID:9987705, PMID:9542475