Promethazine
Promethazine. Phenothiazine first-generation H1 antihistamine + D2 antagonist + muscarinic antagonist. Sedating antiemetic + motion-sickness… Oral half-life 20 h.
Phenothiazine first-generation H1 antihistamine + D2 antagonist + muscarinic antagonist. Sedating antiemetic + motion-sickness agent. IV extravasation causes severe tissue necrosis — black-box prefers deep IM or central line.
PK: A NEW DEFECT SHAPE — A DROPPED LEADING DIGIT. V 970 is 1970 with its first digit lost: "Promethazine disposition is characterised by a large volume of distribution (1970 l) and a high blood clearance (1.14 l min-1)". The same paper states this record F verbatim ("the oral availability of promethazine is only 25%"), which the previously cited study gives only as an interval, "12.3 to 40%". THE FIX CANNOT BE APPLIED TO V ALONE: {970, 12 h} implies a clearance 18% BELOW the published figure and {1970, 12 h} implies 67% ABOVE it; only the coherent pair {1970 L, 20 h} works, and that half-life is DERIVED from the paper own volume and clearance rather than quoted, which is recorded here rather than hidden. The stored 12 h was itself the midpoint of a REVIEW range, "promethazine 10 to 14 hours". MATRIX CAVEAT: this study measured BLOOD, not plasma. My suspicion that one PMID could not serve both routes was REFUTED — it dosed "75 mg (orally) and ... 50 mg (intravenously)". ka 0.7 dropped. Two routes declared with no parameters are removed.
Pharmacokinetics
- Oral — t½ 20 h · F 25% · Vd 1970 L
- IV — t½ 20 h · F 100% · Vd 1970 L
Sources: PMID:8147942, PMID:11922397, PMID:1912125, PMID:6849764