Cetirizine
Cetirizine. Second-generation H1 antagonist — carboxylic acid form of hydroxyzine; reduced BBB penetration but slightly more sedating than… Oral half-life 7.4 h.
Second-generation H1 antagonist — carboxylic acid form of hydroxyzine; reduced BBB penetration but slightly more sedating than loratadine / fexofenadine. Renally cleared.
PK: ka 4 IS CONTRADICTED BY THIS RECORD OWN REFERENCE, which states "a rapid absorption phase (Ka = 1.0-1.4 h(-1))" — about three times too fast — and no scalar can be taken from that range. V 35 L was the registry single most common value, shared by 31 records and identical to the resolver default; the measured figure is 34.7 L but it is APPARENT, so storing 35 beside F 0.7 gave an effective 50 L, 44% above the only measurement. F is pinned to 1. Parent inheritance from hydroxyzine was checked and is CLEAN — cetirizine is hydroxyzine active metabolite, but none of its numbers came from the parent. THE EFFECT MODEL IS A CLASS MISMATCH, NOT A WRONG NUMBER: the record cites a study that fits an INDIRECT-RESPONSE model, and its own quote verifies — peak concentration at 1 h against maximal effect at about 6 h — which an effect compartment at the stored rate cannot reproduce either.
Pharmacokinetics
- Oral — t½ 7.4 h · F 100% · Vd 34.7 L
Sources: PMID:10543317, PMID:11809864, PMID:15889300