Oxybutynin
Oxybutynin. Anticholinergic + direct antispasmodic — competitive M3 muscarinic antagonist on detrusor + spasmolytic on bladder smooth muscle.… Oral half-life 2 h.
Anticholinergic + direct antispasmodic — competitive M3 muscarinic antagonist on detrusor + spasmolytic on bladder smooth muscle. First-line for overactive bladder. Anticholinergic burden — Beers-list problematic in elderly (cognitive impairment + dementia signal at chronic exposure).
PK: THE STORED HALF-LIVES MADE CLEARANCE ROUTE-DEPENDENT, WHICH IS IMPOSSIBLE. Against one volume, 2 h orally and 7.5 h transdermally imply a clearance 3.75 times lower through skin than through vein. The transdermal figure is a skin-depot flip-flop artefact encoded as disposition ON TOP of an already-explicit 96-hour zero-order input, counting the sustained release twice; one disposition value now serves both routes. The half-life and bioavailability were both correct but cited to a paper containing neither — an OROS controlled-release study reporting only relative bioavailability — and are re-sourced to the study that states them, which included intravenous arms so the volume pairing is legitimate. The zero-order duration is likewise real but belonged to an uncited paper. ka 2 EQUALS THE RECORD OWN HALF-LIFE IN HOURS, and here the copy direction is identifiable: the half-life is independently sourceable while no absorption rate exists anywhere, so the half-life was reused as a rate. THE ACTIVE METABOLITE CHANGES BY ROUTE: its ratio to parent is 4.1 orally against 1.2 transdermally, and the anticholinergic burden tracks the metabolite — which is precisely why the patch causes less dry mouth, an effect a parent-only model cannot show. A reference is a medicinal-chemistry paper on rat bladder.
Pharmacokinetics
- Oral — t½ 2 h · F 6% · Vd 193 L
- Transdermal — t½ 2 h · F 100% · Vd 193 L
Sources: PMID:10073329, PMID:3234461, PMID:12608543, PMID:11496941, PMID:11939551