Ethambutol
Ethambutol. Anti-TB agent — inhibits arabinosyl transferase blocking mycobacterial cell wall arabinan biosynthesis. Bacteriostatic component of… Oral half-life 3 h.
Anti-TB agent — inhibits arabinosyl transferase blocking mycobacterial cell wall arabinan biosynthesis. Bacteriostatic component of standard 4-drug TB regimen. Dose-dependent optic neuritis (red-green color blindness) requires baseline + monthly visual checks.
PK: THE ACQUITTAL OF ITS BATCH — THE NUMBERS ARE RIGHT AND ONLY THE CITATION WAS EMPTY. Against an intravenous benchmark stating "Plasma EMB clearance ranged from 7.47 to 8.87 ml/min/kg (mean 8.57)", the stored volume and half-life imply a true clearance within 5.7% and an apparent clearance within 2.6%. AND THE AUTHORING WAS SUBTLER THAN IT LOOKS: V 147 L is deliberately NOT the published steady-state volume of 3.89 L/kg, which would have overstated clearance 1.7x; it is close to the terminal-phase volume, which is the CORRECT one-compartment flattening. Whoever wrote this record got class 12 right before the class had a name. The defects are bibliographic: the cited bioequivalence study reports only 90% confidence intervals — "For ethambutol, these values were 84.7 to 105.7, 93.5 to 105.1, and 92.1 to 105.4" — and not one absolute parameter. F 0.80 is numerically fine but is probably an excretion fraction, "The fraction of the dose eliminated UNCHANGED varied from 0.75 to 0.84", which is a confirmed collision shape and the likely origin of the textbook figure; it moves to a measured absolute value, "Absolute bioavailability in the fasted state and the fed state was ... 87% and 82% for ethambutol", which also IMPROVES the clearance agreement. A POPULATION MODEL WAS REJECTED WITH PREJUDICE: its 77.4 L/h and 76.2 L imply a 0.68 h half-life and are the central compartment of a four-transit model.
Pharmacokinetics
- Oral — t½ 3 h · F 87% · Vd 147 L
Sources: PMID:23410999, PMID:7431225, PMID:26661397