title: Michaelis-Menten absorption kinetics in drugs: - examples and implications.
abstract: It is shown that the absorption of phenylbutazone, naproxen, and chlorthiazide is governed by a dose limiting mechanism. This dose dependency may be explained by a saturation absorption process mathematically obeying Michaelis-Menten type kinetics. Observed dose relationships for tetracycline, fenclozic acid and related compounds, phenytoin, and possibly digoxin and digitoxin may be explained if a saturable process in absorption is postulated. This behavior may be produced by insolubility of the drug compound, a limited "window of absorption" in the gastrointestinal tract, or a capacity limited absorption because of the carrier or the transport mechanism involved. The need for suitably designed dose response studies with new drug compounds is discussed.
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism; D001682:Biological Availability; D002740:Chlorothiazide / Q000378:metabolism; D004798:Enzymes / Q000378:metabolism; D007700:Kinetics; D007769:Lactams; D009288:Naproxen / Q000378:metabolism; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D010653:Phenylbutazone / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D004798:Enzymes; D007769:Lactams; D004364:Pharmaceutical Preparations; D009288:Naproxen; D002740:Chlorothiazide; D010653:Phenylbutazone