Omalizumab
Omalizumab, a biologic. Humanised IgG1κ mAb binding free IgE at the Cε3 domain (the FcεRI-binding site) → forms soluble… Subcutaneous half-life 26 d.
Humanised IgG1κ mAb binding free IgE at the Cε3 domain (the FcεRI-binding site) → forms soluble trimeric/hexameric complexes that cannot engage FcεRI on mast cells/basophils. Downregulates FcεRI expression over weeks. Chronic suppression of allergic cascade.
V_L CORRECTED 5.6 -> 5.9 L. The stored 5.6 was the protein default (0.08 L/kg x 70 kg) wearing a citation that states a different figure: PMID:17096680 verbatim, "the volume of distribution for omalizumab and IgE 5900 +/- 107 ml, and that for the complex 3630 +/- 223 ml". Two caveats carried with it: this is a population-model volume for the drug-ligand compartment, and the 3.63 L in the same sentence belongs to the COMPLEX and must not be mistaken for it; and the paper adds "Clearance and volume of distribution for omalizumab varied with bodyweight", so a 70 kg-referenced scalar is an approximation the paper does not itself endorse. PK: ABSORPTION RATE AUTHORED FROM THE XOLAIR LABEL. This row carried no ka, so the solver substituted 1.0/h and put the peak at 6.8 h. Source, verbatim from the current FDA label (DailyMed setid 7f6a2191-adfb-48b9-9bfa-0d9920479f0d): "omalizumab was absorbed slowly, reaching peak serum concentrations after an average of 7–8 days." RANGE: the shorter endpoint is taken. PUBMED HAS THIS NOWHERE — 27 targeted searches across two passes returned four usable peak times for this whole class, because Tmax is a label figure that rarely reaches an abstract. A regulatory label is already a first-class source in this schema. With the stored half-life fixing ke, Tmax solves uniquely for ka by inverting the model own definition, ln(ka/ke)/(ka-ke) = Tmax — ARITHMETIC, NOT AN ESTIMATE — giving 0.01753/h, which reproduces 168 h on substitution. EXPOSURE IS UNCHANGED: the absorption rate cancels out of AUC, so only the shape moves.
Pharmacokinetics
- Subcutaneous — t½ 26.0 d · F 62% · ka 0.01753 h⁻¹ · Vd 5.9 L
Sources: PMID:17096680, PMID:31913280