51. Pharmacokinetics of promethazine and its sulphoxide metabolite after intravenous and oral administration to man
- Author
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JB Houston, G Taylor, G Mawer, and Jonathan Shaffer
- Subjects
Adult ,Male ,Metabolite ,Administration, Oral ,Pharmacology ,Promethazine ,Route of administration ,First pass effect ,chemistry.chemical_compound ,Pharmacokinetics ,Oral administration ,Medicine ,Humans ,Pharmacology (medical) ,Volume of distribution ,business.industry ,Area under the curve ,Kinetics ,chemistry ,Injections, Intravenous ,business ,medicine.drug ,Half-Life ,Research Article - Abstract
Blood concentrations of promethazine and promethazine sulphoxide have been measured following oral and intravenous administration of promethazine to seven healthy male volunteers. Promethazine disposition is characterised by a large volume of distribution (1970 1) and a high blood clearance (1.141 min-1). Less than 1% of the dose is excreted unchanged in the urine, therefore total body clearance is essentially metabolic clearance. In accord with this high clearance the oral availability of promethazine is only 25%. The absorption of promethazine from the gastrointestinal tract exceeds 80% in most subjects. Minimal metabolism by the gastrointestinal mucosa is implicated. Promethazine sulphoxide pharmacokinetics are consistent with a pronounced first pass effect. Although the area under the curve for this metabolite is not route dependent, there is a marked alteration in the shape of the metabolite curve when oral and intravenous data are compared. Evidence is presented to support the hypothesis that S-oxidation of promethazine is predominantly an hepatic event. The conclusions of previous investigators with regard to the role of the gut mucosa in S-oxidation of phenothiazines is critically assessed.
- Published
- 1983