Naltrexone
Naltrexone. Pure µ-opioid receptor antagonist — competitive blockade with no agonist activity. Approved for alcohol use disorder + opioid use… Oral half-life 8.9 h.
Pure µ-opioid receptor antagonist — competitive blockade with no agonist activity. Approved for alcohol use disorder + opioid use disorder relapse prevention. Hepatotoxicity warning at high doses (>300 mg/d). LDN at 1–4.5 mg used off-label for autoimmune / fibromyalgia.
PK: t½ 4 h IS NEITHER OF ITS OWN PAPER TWO VALUES — "2.7 hr, iv; 8.9 hr, oral" — it is the textbook round number sitting between them; the oral value now goes on the oral row. F 0.05 is the BOTTOM ENDPOINT of a quoted 5-40% band, and the only measured estimate runs four-fold the other way, but that figure is a first-pass complement rather than a stated bioavailability, so it is not substituted. I PROPOSED STRIPPING THIS RECORD AND WAS ARGUED OUT OF IT, correctly: `uncharacterized` means no primary publishes a modelled parameter, and that is false here — this drug pharmacokinetics ARE characterised. WHAT FAILS IS THE PLASMA-TO-EFFECT LINK, AND IT IS NOT A TWO-ANALYTE PROBLEM EITHER: human receptor-occupancy imaging found that "for both NTX and its principal active metabolite in humans, 6-beta-NTX, this relationship was INDIRECT", so neither plasma species predicts blockade, which "persisted for 5 days after discontinuation". That is slow receptor dissociation, which no half-life can express. The depot route is removed: its half-life was the oral value against a measured 5-7 DAYS, and its release duration of 720 h is a one-month convenience matching neither the 28-day interval nor the 31-day window.
Pharmacokinetics
- Oral — t½ 8.9 h · F 5% · Vd 1350 L
Sources: PMID:6114837, PMID:10463317, PMID:21502953